Risk Factors (Genetics & Inherited Conditions)
Individuals have a higher risk of developing allergies if they have family members with allergies or asthma. They also have a higher risk of developing an allergy if they have asthma or one or more allergies already. Children are more likely to develop allergies than are adults, and allergies are more common in firstborn children and among children in smaller families. Allergies are also more common in urban than in rural environments and more common in developed than in developing countries. Other environmental factors (such as exposure to cigarette smoke and pollution) as well as medical factors (such as infections, autoimmune disease, diet, and stress) can also affect allergy risk.
(The entire section is 110 words.)
Etiology and Genetics (Genetics & Inherited Conditions)
Multiple factors modulate risk for allergic diseases, without a single causal agent; however, the most important component influencing whether a person will develop allergies is genetic predisposition. Atopy, characterized by high levels of immunoglobulin E (IgE), is the condition that underlies allergic diseases and is highly influenced by genetics. People who have a genetic predisposition toward developing allergic conditions have ten to twenty times the risk of developing allergies than those who do not. If one or more of a person’s parents or siblings have allergies, the risk for developing allergies is 30 to 50 percent or 25 to 35 percent, respectively. Monozygotic twins, who share 100 percent of their DNA, are more likely to have the same type of allergy than are dizygotic twins, who share 50 percent of their DNA, suggesting that genetic factors are important in allergy risk. Even in monozygotic twins, however, only about 50 to 60 percent of twins share the same allergic condition, demonstrating that nongenetic factors also influence allergies. As a result, allergy is considered a complex genetic disease because it does not follow the laws of Mendelian inheritance.
Because multiple allergic conditions exist and allergies are also influenced by exposure to allergens, determining specific genetic risk factors for allergies is challenging. Nevertheless, several candidate susceptibility genes for allergic diseases...
(The entire section is 616 words.)
Symptoms (Genetics & Inherited Conditions)
Allergy symptoms vary widely. Sneezing, runny nose, and sore throat are common with seasonal allergies, sometimes called hay fever or allergic rhinitis. Allergic reactions can also affect the eyes, leading to redness, watery or itchy eyes, and swelling. Sometimes, allergies may affect the skin, leading to rashes or hives. More severe allergic reactions can lead to anaphylaxis, which may include the symptoms listed above in addition to low blood pressure or shock.
(The entire section is 72 words.)
Screening and Diagnosis (Genetics & Inherited Conditions)
A doctor may perform a skin test or blood test to test for allergies. In a skin test, a small drop of the possible allergen is either placed onto skin followed by scratching with a needle over the drop or injected into the skin. With skin tests, if the individual is allergic to a substance, the test site will become red, swollen, and itchy within twenty minutes. Another way to test for allergies involves taking a blood sample. The medical laboratory adds the allergen to the blood and then measures the immune response to the allergen. If the body produces many antibodies to attack the allergen, then the individual is allergic to the tested substance.
(The entire section is 115 words.)
Treatment and Therapy (Genetics & Inherited Conditions)
Several medications are available to relieve allergies. Oral and nasal antihistamines, such as Benadryl and Claritin, help with allergy symptoms by blocking the action of histamine, a substance the body releases during an allergic reaction. Nasal sprays containing corticosteroids, such as Nasonex and Flonase, or nonsteroidal anti-inflammatory drugs (NSAIDs), such as NasalCrom, are sprayed into the nose to reduce inflammation. Decongestants can also be used to alleviate allergy symptoms, sometimes in combination with antihistamines, as in Allegra D. Leukotriene receptor antagonists, such as Singulair, are another treatment that may be used to reduce inflammation-related allergy symptoms.
Immunotherapy, or allergy shots, is another treatment for allergies. People who receive immunotherapy have small amounts of allergens injected into their bodies. The doses of these allergens are increased over at least three to five years in order to develop the body’s immunity to them. When the patient experiences minimal symptoms for two seasons or more, the treatment is stopped.
(The entire section is 157 words.)
Prevention and Outcomes (Genetics & Inherited Conditions)
The simplest way to prevent allergic conditions or to reduce symptoms is to minimize exposure to the problematic allergen. For example, delaying the time at which infants are first exposed to highly allergenic foods such as cow’s milk and peanuts may help prevent allergy development. Eating a healthy diet and managing stress effectively can also help prevent and alleviate allergy symptoms.
(The entire section is 62 words.)
Further Reading (Genetics & Inherited Conditions)
Contopoulos-Ioannidis, D. G., I. N. Kouri, and J. P. Ioannidis. “Genetic Predisposition to Asthma and Atopy.” Respiration 74, no. 1 (2007): 8-12.
Grammatikos, A. P. “The Genetic and Environmental Basis of Atopic Diseases.” Annals of Medicine 40, no. 7 (2008): 482-495.
Thomsen, S. F., K. O. Kyvik, and V. Backer. “Etiological Relationships in Atopy: A Review of Twin Studies.” Twin Research and Human Genetics 11, no. 2 (2008): 112-120.
Torres-Borrego, J., A. B. Molina-Terán, and C. Montes-Mendoza. “Prevalence and Associated Factors of Allergic Rhinitis and Atopic Dermatitis in Children.” Allergologia et Immunopathologia 36, no. 2 (2008): 90-100.
(The entire section is 86 words.)
Web Sites of Interest (Genetics & Inherited Conditions)
Causes and Symptoms (Magill’s Medical Guide, Sixth Edition)
Allergies represent inappropriate immune responses to intrinsically harmless materials, or antigens. Most allergens are common environmental antigens. Approximately one in every six Americans is allergic to material such as dust, molds, dust mites, animal dander, or pollen. The effects range from a mere nuisance, such as the rhinitis associated with hay fever allergies or the itching of poison ivy, to the life-threatening anaphylactic shock that may follow a bee sting. Allergies are most often found in children, but they may affect any age group.
Allergy is one of the hypersensitivity reactions generally classified according to the types of effector molecules that mediate their symptoms and according to the time delay that follows exposure to the allergen. P. G. H. Gell and Robin Coombs defined four types of hypersensitivities. Three of these, types 1 through 2, follow minutes to hours after the exposure to an allergen. Type 4, or delayed-type hypersensitivity (DTH), may occur anywhere from twenty-four to seventy-two hours after exposure. People are most familiar with two of these forms of allergies: type 1, or immediate hypersensitivity, commonly seen as hay fever or asthma; and type 4, most often following an encounter with poison ivy or poison oak.
Type 1 hypersensitivities have much in common with any normal immune response. A foreign material, an allergen, comes in contact with the host’s immune system, and...
(The entire section is 1681 words.)
Treatment and Therapy (Magill’s Medical Guide, Sixth Edition)
Three methods for dealing with allergies exist: avoidance of the allergen, palliative treatments, and desensitization. Ideally, one can attempt to avoid the allergen. For example, cow’s milk, a common allergen, should not be given to a child at too young an age, and one can stay away from patches of poison ivy or avoid eating strawberries if one is allergic to them.
Avoidance, however, is not always possible or desirable, as the problem may be the fur, for example, from the family cat. In any event, it is sometimes difficult to identify the specific substance causing the symptoms. This is particularly true when dealing with foods. Various procedures exist to identify the irritating substance, skin testing being the most common. In this procedure, the patient’s skin is exposed to small amounts of suspected allergens. A positive test is indicated by formation of hives or reddening within about twenty to thirty minutes. If the person is hypersensitive to a suspected allergen and finds a skin test too risky, then a blood test (RAST) may be substituted. In addition to running a battery of tests, a patient’s allergy history (including family history, since allergies are in part genetic) or environment may give clues as to the identity of the culprit.
The most commonly used method of dealing with allergies is a palliative treatment—that is, treatment of the symptoms. Antihistamines act by binding to histamine...
(The entire section is 909 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Though allergies in humans have probably existed since humans first evolved from ancestral primates, it was only in the nineteenth century that an understanding of the process began to develop. Type 1 hypersensitivity reaction was first described in 1839 through experiments in which dogs were repeatedly injected with egg albumin and developed an immediate fatal shock. The term “anaphylaxis” was coined for this phenomenon in 1902, when Paul Portier and Charles Richet observed that dogs repeatedly immunized with extracts of sea anemone tentacles suffered a similar fate. Richet was awarded the 1913 Nobel Prize in Physiology or Medicine for his work on anaphylaxis.
In the 1920’s, Sir Henry Dale established that at least some of the phenomena associated with immediate hypersensitivity were caused by the chemical histamine. Dale sensitized guinea pigs against various antigens. He then observed that, when the muscles from the uterus were removed and exposed to the same antigen, histamine was released and the muscles underwent contraction (known as the Schultz-Dale reaction).
The existence of a component in human serum which mediates hypersensitive reactions was demonstrated by Otto Prausnitz, a Polish bacteriologist, and Heinz Kustner, a Polish gynecologist, in 1921. Kustner had a strong allergy to fish. Prausnitz removed a sample of serum from his colleague and injected it under his own skin. The next day,...
(The entire section is 602 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
Adelman, Daniel C., et al., eds. Manual of Allergy and Immunology. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 2002. Examines research developments and the clinical diagnosis and treatment of allergies and immune disorders. Topics include asthma, disorders of the eye, diseases of the lung, anaphylaxis, insect allergies, drug allergies, rheumatic diseases, transplantation immunology, and immunization.
Brostoff, Jonathan, and Linda Gamlin. Food Allergies and Food Intolerance: The Complete Guide to Their Identification and Treatment. Rochester, Vt.: Inner Traditions, 2000. Examines the role of food allergies in chronic health conditions such as migraines and persistent fatigue and gives a step-by-step process for identifying and treating food allergies.
Cutler, Ellen W. Winning the War Against Asthma and Allergies. Albany, N.Y.: Delmar, 1998. This clearly written book provides practical information on all aspects of allergies—what they are, their causes, testing, diagnosis, and treatment, including nontraditional therapies. Preventive measures are covered, as are scenarios for various allergy elimination therapies.
Delves, Peter J., et al. Roitt’s Essential Immunology. 11th ed. Malden, Mass.: Blackwell, 2006. Written by a leading author in the field, the text provides a fine description of immunology. The section on hypersensitivity is clearly presented...
(The entire section is 463 words.)
Allergies (Encyclopedia of Medicine)
Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.
Allergies are among the most common of medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.
An allergy is a type of immune reaction. Normally, the immune system responds to foreign microorganisms or particles by producing specific proteins called anti-bodies. These antibodies are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of chemical reactions designed to protect the body from infection. Sometimes, this same series of reactions is triggered by harmless, everyday substances such as pollen, dust, and animal danders. When this occurs, an allergy develops against the offending sub-stance (an allergen.)
Mast cells, one of the major players in allergic reactions, capture and display a particular type of antibody, called immunoglobulin type E (IgE) that binds to allergens. Inside mast cells are small...
(The entire section is 4357 words.)
Allergy (Encyclopedia of Science)
An allergy is an extreme or overly sensitive response of the immune system to harmless substances in the environment. The immune system launches a complex series of actions against an irritating substance, referred to as an allergen. This immune response may be accompanied by a number of stressful symptoms, ranging from mild to severe to life-threatening. In rare cases, an allergic reaction leads to anaphylactic shock condition characterized by a sudden drop in blood pressure, difficulty in breathing, skin irritation, collapse, and possible death.
The immune system may produce several chemical agents that cause allergic reactions. One example are the histamines released after exposure to an allergen. (Histamines are compounds that cause capillaries to dilate; smooth muscles to contract, thereby constricting airways; and gastric acids to be secreted.) The use of antihistamines helps to relieve some of the symptoms of allergy by blocking out histamine receptor sites in cells.
Types of allergy
The most common type of allergy is allergic rhinitis (inflammation of the mucous membrane of the nose) caused by inhaling allergens carried in the air. Seasonal environmental allergic rhinitis, or hay fever as it is popularly called, is brought on by wind-borne pollens, the dustlike masses of microscopic spores in seedbearing plants. Every spring, summer,...
(The entire section is 1195 words.)
Allergies (Encyclopedia of Children's Health)
Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.
Allergies are among the most common of medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.
Allergies are a type of immune reaction. Normally, the immune system responds to foreign microorganisms, or particles, like pollen or dust, by producing specific proteins, called antibodies, that are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. When this same series of reactions is triggered by harmless, everyday substances, it is called an allergy. The substance that causes the allergy is called an allergen.
All allergic reactions involve a special set of cells in the immune system known as mast cells. Mast cells, found in the lining of the nasal passages and eyelids,...
(The entire section is 3812 words.)
Allergies (Encyclopedia of Alternative Medicine)
Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.
Allergies are among the most common medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.
An allergy is a type of immune reaction. Normally, the immune system responds to foreign bodies, like pollen or bacteria, by producing specific proteins called antibodies that are capable of binding to identifying molecules (antigens) on the foreign body. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. Harmless, everyday substances trigger this same series of reactions. This is the condition known as allergy, and the offending substance is called an allergen.
Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system.
- Airborne allergens cause the sneezing, runny nose, and itchy, bloodshot eyes of hay fever (allergic rhinitis)....
(The entire section is 2415 words.)
Allergies (Encyclopedia of Nursing & Allied Health)
Allergies are among the most common of medical disorders. About one quarter of all Americans suffer from some form of allergy, such as asthma, allergic rhinitis (hay fever), or atopic dermatitis (eczema). Allergy is the single largest reason for school absence; allergic rhinitis alone is responsible for two million school day absences annually. Allergies cause one out of nine physician visits and are responsible for significant losses of productivity in the workplace.
An allergy is a type of immune reaction. Normally, the immune system responds to bacteria, viruses, or particlesuch as pollen or dusty producing antibodies (specific proteins) capable of binding to antigens (identifying molecules) on the foreign particle. The interaction between the antibody and antigen sets off a series of reactions designed to protect the body from infection. When this same series of reactions is triggered by harmless, everyday substances, it is known as an allergy, and the offending substance is called an allergen.
Allergens enter the body through four main routes: the airways, skin, gastrointestinal tract, and the circulatory system.
- Airborne allergens cause the sneezing, runny nose of allergic rhinitis. Airborne allergens can also affect the lining of the lungs, causing asthma, or the conjunctiva of the eyes, causing conjunctivitis (pink eye).
- Allergens in food may cause itching and swelling of the lips and throat, cramps, and diarrhea. When absorbed into the bloodstream, they may cause urticaria (hives) or more severe reactions such as swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and a sudden drop in blood pressure.
- Allergins that come in direct contact with the skin can cause reddening, itching, and blistering (contact dermatitis). Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This reaction is known as atopic dermatitis or eczema.
- Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulatory system. There they may cause systemwide responses (including anaphylaxis), as well as local reactions of swelling and irritation at the injection site.
Individuals with allergies are not equally sensitive to all allergens. For example, some may have severe allergic rhinitis but no food allergies, others are extremely sensitive to nuts but not to any other food. Allergies may worsen over time. For example, childhood ragweed allergy may progress to year-round dust and pollen allergy. On the other hand, an individual may lose allergic sensitivity. Infant or childhood atopic dermatitis almost always disappears with advancing age. More commonly, an individual's apparently diminished sensitivity may instead be attributable to reduced exposure to allergens or an increased tolerance for allergy symptoms.
Causes and symptoms
Mast cells involved in allergic reactions capture and display an antibody, called immunoglobulin E (IgE), that binds to allergens. After the allergen is bound, mast cell granules release a variety of potent chemicals, including histamine, that are responsible for some of allergic symptoms.
Immunologists distinguish allergic reactions into two main types: immediate hypersensitivity reactions, which are mainly mast cell-mediated and occur within minutes of contact with allergen, and delayed hypersensitivity reactions, mediated by T cells (a type of white blood cells) and occurring hours to days after exposure.
Inhaled or ingested allergens usually cause immediate hypersensitivity reactions. Allergens bind to IgE antibodies on the surface of mast cells, which release the contents of their granules onto neighboring cells, including blood vessels and nerve cells. Histamine binds to the surfaces of these other cells through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes increased leakage, thereby producing fluid collection, swelling, and redness. Histamine also stimulates pain receptors, making tissue more sensitive and irritable. Symptoms last from one to several hours following contact.
In the upper airways and eyes immediate hypersensitivity reactions cause the runny nose and itchy, bloodshot eyes typical of allergic rhinitis. In the gastrointestinal tract these reactions lead to swelling and irritation of the intestinal lining, causing the cramping and diarrhea typical of food allergy. Allergens that enter the circulatory system may cause hives, angioedema, anaphylaxis, or atopic dermatitis.
Allergens on the skin usually cause delayed hypersensitivity reaction. Roving T cells contact the allergen, setting in motion a more prolonged immune response. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.
THE ROLE OF INHERITANCE. While allergy to specific allergens is not inherited, the likelihood of developing some type of allergy seems to be, at least for many people. If neither parent has allergies, then the chances of a child developing allergy is approximately 100%; when one parent has allergies, it is 300%; and when both have allergies, it is 405%. Allergy patients share a genetic predisposition to produce higher levels of IgE in response to allergens. Those who produce more IgE will develop a stronger allergic sensitivity.
COMMON ALLERGENS. The most common airborne allergens are the following:
- plant pollens
- animal fur and dander
- body parts from house mites (microscopic creatures found in all houses)
- house dust
- mold spores
- cigarette smoke
Common food allergens include the following:
- nuts, especially peanuts, walnuts, and Brazil nuts
- fish, mollusks, and shellfish
- food additives and preservatives
The following types of drugs commonly cause allergic reactions:
- penicillin or other antibiotics
- flu vaccines
- tetanus toxoid vaccine
- gamma globulin
Common causes of contact dermatitis include:
- poison ivy, oak, and sumac
- nickel or nickel alloys
Insects and other arthropods whose bites or stings typically cause allergy include:
- bees, wasps, and hornets
Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose, often with a scratchy or irritated throat due to post-nasal drip. Allergic conjunctivitis (inflammation of
the thin membrane covering the eye) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether it is spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat, and nausea, cramping, diarrhea, and gas. Contact dermatitis is marked by reddened, itchy, weepy skin blisters.
Systemic reactions may occur from any type of allergen, but are more common following ingestion or injection of an allergen. Skin reactions include hives and angioedema (a deeper and more extensive skin reaction) involving more extensive fluid collection. Anaphylaxis is marked by airway constriction, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, and, in some cases, loss of consciousness.
Allergies may often be diagnosed by taking a detailed medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy tests may be used to identify potential allergens. These tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. Reaction will occur on the skin even if the allergen is normally encountered in food or in the airways.
RAST testing, performed by a laboratory technologist, is a blood test that measures the level of reactive IgE antibodies in the blood. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount.
A variety of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.
ANTIHISTAMINES. Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they may be even more effective when used before symptoms appear. A wide variety of antihistamines are available.
Some antihistamines produce drowsiness as a major side effect. These include:
- diphenhydramine (Benadryl and generics)
- chlorpheniramine (Chlor-trimeton and generics)
- brompheniramine (Dimetane and generics)
- clemastine (Tavist and generics)
Antihistamines that do not cause drowsiness are available by prescription and include the following:
- astemizole (Hismanal)
- loratidine (Claritin)
- fexofenadine (Allegra)
- azelastin HCl (Astelin)
Hismanal has the potential to cause serious heart arrhythmia when taken with the antibiotic erythromycin, the antifungal drugs ketoconazole and itraconazole, or the antimalarial drug quinine. Exceeding the recommended dose of Hismanal may also cause arrhythmia.
DECONGESTANTS. Decongestants constrict blood vessels to counteract the effects of histamine. Nasal sprays, applied directly to the nasal lining and oral systemic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of topical decongestants for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.
TOPICAL CORTICOSTEROIDS. Topical corticosteroids reduce mucous membrane inflammation and are available by prescription. Allergies tend to worsen as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Topical corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. As a result, they are best started before allergy season begins. Side effects are usually mild, but may include headaches, nosebleeds, and unpleasant taste sensations.
MAST CELL STABILIZERS. Cromolyn sodium prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. It acts as a preventive treatment if it is begun several weeks before the onset of the allergy season. It also may be used for year round allergy prevention. Cromolyn sodium is available as a nasal spray for allergic rhinitis and in aerosol (a suspension of particles in gas) form for asthma.
Immunotherapy, also known as desensitization or allergy shots, alters the balance of antibody types in the body, thereby reducing the ability of IgE to cause allergic reactions. Immunotherapy is preceded by allergy testing to determine the precise allergens responsible. Injections involve very small but gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take as long as several years to achieve, and are not seen at all in about one in five patients. Patients are monitored closely following each shot because of the small risk of anaphylaxis.
Because allergic reactions involving the lungs cause the airways or bronchial tubes to narrow (as in asthma), bronchodilators, which cause the smooth muscle lining the airways to dilate, can be very effective. Some bronchodilators used to treat acute asthma attacks include adrenaline, albuterol, or other adrenergic stimulants, most often administered as aerosols. Theophylline, naturally present in coffee and tea, is another drug that produces bronchodilation. It is usually taken orally, but in a severe asthma attack is may be administered intravenously. Other drugs, including steroids, are used to prevent asthma attacks and in the long-term management of asthma.
Treatment of contact dermatitis
Calamine lotion applied to affected skin can reduce irritation. Topical corticosteroid creams are more effective, though overuse may lead to dry and scaly skin.
Treatment of anaphylaxis
The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. Patients prone to anaphylaxis in response to food or insect allergies often carry an "Epi-pen" containing adrenaline in a hypodermic needle. Prompt injection may prevent a more serious reaction from developing.
Allergies may improve over time, although they often worsen. While anaphylaxis and severe asthma are life threatening, other allergic reactions are not. Learning to recognize and avoid allergy-provoking situations allows most patients with allergies to lead normal lives.
Health care team roles
Diagnosis and effective management of allergy symptoms involves cooperation and collaboration between the patient and an interdisciplinary team of health care professionals. The patient's primary care physician or pediatrician, allergy and immunology specialists, laboratory technologists, respiratory therapists, pharmacists, pharmacy assistants, and health educators are involved in helping patients and families gain an understanding of how to prevent effectively manage symptoms.
Nurses, respiratory therapists, and health educators help patients learn how to prevent and manage allergy symptoms. They teach patients how to distinguish mild allergy symptoms from those requiring immediate medical attention. Pharmacists and pharmacy assistants may offer additional instruction about medication use and reiterate the importance of adhering to prescribed treatment.
Avoiding allergens is the best means of limiting allergic reactions. For food allergies, there is no effective treatment except avoidance. By determining the allergens that cause reactions, most patients can learn to avoid allergic reactions from food, drugs, and contact allergens such as poison ivy or latex. Airborne allergens are more difficult to avoid, although keeping dust and animal dander from collecting in the house may limit exposure. Cromolyn sodium can prevent mast cell degranulation, thereby limiting the allergic response.
Allergen substance that provokes an allergic response.
Allergic rhinitisnflammation of the mucous membranes of the nose and eyes in response to an allergen; also known as hay fever.
Anaphylaxisncreased sensitivity caused by previous exposure to an allergen that can result in blood vessel dilation and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.
Angioedemaevere non-inflammatory swelling of the skin, organs, and brain that can also be accompanied by fever and muscle pain.
Antibody specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Antigen foreign protein to which the body reacts by making antibodies.
Asthma lung condition where the airways become constricted due to smooth muscle contraction, causing wheezing, coughing, and shortness of breath.
Atopic dermatitisnflammation of the skin as a result of exposure to airborne or food allergens; also known as eczema.
Conjunctivitisnflammation of the thin lining of the eye called the conjunctiva.
Contact dermatitisnflammation of the skin as a result of contact with a substance.
Delayed hypersensitivity reactionsllergic reactions mediated by T cells that occur hours to days after exposure.
Granulesmall packets of reactive chemicals stored within cells.
Histamine chemical released by mast cells that activates pain receptors and causes cells to become leaky.
Immune hypersensitivity reactionllergic reactions that are mediated by mast cells and occur within minutes of allergen contact.
Mast cells type of immune system cell found in the lining of the nasal passages and eyelids, with an antibody called immunoglobulin type E (IgE) on its cell surface; mast cells release histamine from intracellular granules.
Walsh, William. Food Allergies: The Complete Guide to Understanding and Relieving Your Food Allergies. John Wiley and Sons, 2000.
The Washington Manual of Medical Therapeutics. 30th ed. Philadelphia: Lippincott Williams & Wilkins, 2001.
Young, Stuart, et al. Allergies: The Complete Guide to Diagnosis, Treatment, and Daily Management. Plume, 1999.
Allergies (Encyclopedia of Food & Culture)
ALLERGIES. Food allergy has been recognized since the time of Hippocrates. People with adverse reactions to food can be difficult to evaluate because overlap exists between true food allergy and toxic and other reactions to chemicals or other food ingredients. The incidence of food allergy is increasing in the industrialized world, raising questions about the interactive effects between environmental and genetic factors. There is a considerable burden on society in terms of cost of treatment, death from anaphylactic reactions, and the anxiety produced by real or perceived food allergy. Avoidance of the food is the current treatment, but new strategies are being developed.
Adverse reactions to the ingestion of food that can be reproduced is termed intolerance or hypersensitivity. Since this does not imply an underlying cause, it may encompass immune or nonimmune mechanisms. For example, chemicals such as caffeine may cause reproducible symptoms, but this is not mediated by the immune system. True food allergy or food hypersensitivity is defined as a reproducible adverse reaction to food caused by the immune system creating antibodies or cellular inflammation.
Type I IgE-mediated food allergy. The classic example is immediate anaphylactic reaction to food. In susceptible individuals after exposure to the food, the immune system creates specific IgE antibodies to that food. IgE is produced by the immune system's B-lymphocytes, and is bound to receptors on the surface of mast cells. Mast cells reside in tissues at body surfaces such as the skin, eyes, nose, throat, lung, and gastrointestinal tract. Mast cells are made up of granules containing chemicals including histamine. When the food protein contacts and binds to adjacent specific IgE molecules at the mast cell surface, a cascade of events occurs leading to degranulation of mast cells and release of chemicals that cause the allergic reaction. This may include skin hives, airway swelling, wheezing, abdominal pain, vomiting and/or diarrhea. This may progress to anaphylaxis, shock, and even death. This reactivity to food can be demonstrated by skin-prick tests, which have been used to diagnose allergy since the 1870s. Food protein is placed on the skin, the skin is scratched or pricked, and a hive will develop in the presence of skin mast cells with IgE directed against the food. In the 1920s Prausnitz and Kustner showed that a substance circulating in the blood of the allergic individual was responsible for a positive skin test, because blood serum could be transferred to the skin of a nonallergic individual resulting in a positive skin test. IgE is that substance, and food-specific IgE can be measured directly in the blood, by means of the IgE RAST (radioallergosorbent) test. Diagnosis of this immediate type of food allergy rests on the history of rapid onset of symptoms, demonstration of positive skin-prick test or specific IgE RAST. Challenging an individual with the food is the ultimate way to prove a food allergy.
Non-IgE-mediated food allergy. Other immune mechanisms can be responsible for allergic reactions to foods. The classic example is celiac disease (celiac sprue or gluten-induced enteropathy). This is an immune system reaction to wheat (gluten). Patients do not have IgE antibody directed against wheat, but exposure to gluten over a period of time causes inflammation of the intestine and a characteristic atrophy or flattening of the normal intestinal villous folds. The diagnosis rests on the characteristic biopsy of the small intestine coupled with another type of antibody (IgA) against wheat protein. Any food may also cause similar intestinal inflammation, leading to varying symptoms and signs depending on the area of the intestine affected. Unlike IgE-mediated allergy or celiac disease, there are no readily available confirmatory tests for these other food allergies.
Food allergy is perceived as being common; however, large studies support the idea that true food allergy is less common than people think. A study of 480 infants from birth to age three revealed 28 percent were suspected by their parents as having food allergy; however, this was confirmed in only 8 percent of this group. The prevalence then decreases with age. Twenty percent of adults suspect food allergy, though allergy is confirmed in only 1 to 2 percent of adults. Although food allergies in adults tend to persist with age, many infants and children out-grow them with time.
Recently, interest has grown over the apparent increase in the prevalence and severity of food allergy. This has paralleled an increase in other atopic disorders such as asthma in industrialized nations compared with children of similar genetic background in developing countries (atopic refers to a tendency to develop allergic conditions such as hay fever, asthma, or food allergies). The "hygiene hypothesis" contends that through evolution, the human immune system has developed with a specific microbial environment, and reduced exposure to microbes in the developed world may lead to increased allergic response. Further study is needed.
Type I Immediate (IgE-Mediated) Hypersensitivity Reactions to Food
Immediate hypersensitivity reactions to foods are most common in young children, with 50 percent of these reactions occurring in the first year of life. The majority is from cow's milk and soy protein from infant formulas. Other foods begin to predominate in older children, including eggs, fish, peanuts, and wheat, and along with milk and soy account for over 90 percent of food allergy in children. Peanut, tree nut, and shellfish allergy predominate in adults. Exposures may occur inadvertently due to improper labeling, changes in product composition with time, and contamination of foods during processing. Symptoms from multiple organ systems may occur, beginning within minutes. Unfortunately, fatal anaphylactic reactions (shock) to food occur despite strict dietary avoidance and treatment of reactions. Families, caregivers, and individuals with a history of anaphylaxis to food require education in diet and in the use of self-administered epinephrine. Individuals should be observed in a hospital setting after a significant reaction. Exercise-induced anaphylaxis to food occurs when the combination of ingesting the food followed by exercise leads to anaphylaxis. Oral allergy syndrome describes symptoms of itching of the mouth and throat often attributable to eating fruits, and typically does not progress. Chronic hives or urticaria can be caused by foods, but it is a common misconception that these conditions are usually food-related; only in 1 to 2 percent of cases is urticaria or chronic hives a reaction to food. Atopic dermatitis (AD) or eczema is a chronic skin condition found in atopic individuals. Patients with AD have a 30 to 40 percent prevalence of food allergy.
Investigation and treatment of type I immediate reactions to food. The rapid onset of symptoms after ingestion correlates highly with positive skin-prick or IgE RAST tests to the offending food, making confirmation of immediate hypersensitivity straightforward. Consultation with an allergist and dietitian is recommended. Groups such as the Food Allergy and Anaphylaxis Network can provide support and educational materials.
Non-IgE-Mediated Food Allergy
The spectrum of non-IgE food allergy is quite varied, and the symptoms often parallel the area of inflammation in the gastrointestinal tract (see sidebar). Avoidance of the food will resolve symptoms and intestinal inflammation; rechallenge with the food will reproduce the injury. However, unlike IgE food allergy, symptoms may take days or weeks to resolve or reappear with elimination or exposure respectively, making evaluation even more difficult.
Celiac disease or gluten-induced enteropathy (see sidebar) is a chronic intestinal condition caused by non-IgE mediated allergy to gluten, a protein in wheat and other grains. Chronic exposure to gluten causes inflammation and atrophy of small intestinal folds, leading to symptoms of malabsorption of food. Typically, patients have diarrhea, weight loss, and abdominal bloating. There is a genetic predisposition to celiac disease, but onset may occur at any age, suggesting an environmental factor such as infection may be needed in some individuals to trigger the inflammatory process. The disease has a higher prevalence (up to 1 in 40000) in individuals of eastern European descent. Celiac disease is associated with a skin condition (dermatitis herpetiformis), thyroid disease, diabetes, and Down syndrome.
Allergic or eosinophilic colitis in infants is a common manifestation of non-IgE food protein allergy. It is characterized by diarrhea with blood and mucus. It is caused by milk or soy formula and may occur in breast-fed infants from dietary antigens transmitted through breast milk. Colon biopsy shows allergic inflammation.
Food protein-induced enterocolitis is a severe reaction to food, often delayed four to six hours, without evidence of IgE. Patients present with lethargy, vomiting, and diarrhea. Recovery is within six to eight hours after fluid resuscitation. A careful history usually reveals the offending food, although this may not be appreciated unless multiple episodes occur.
Chronic enteropathy from food allergy can also lead to inflammation with villous atrophy similar to celiac disease. Most patients have diarrhea, in addition to weight loss, anemia, and low albumin from protein loss from the intestine.
Allergic gastritis is inflammation of the stomach with pain and vomiting. As with other non-IgE food allergy, biopsies of the stomach demonstrate allergic (eosinophilic) inflammation.
Allergic esophagitis is characterized by intense eosinophilia of the esophagus on biopsy. Patients complain of pain and problems with swallowing, even to the point of having food impactions in the esophagus. Treatment with hypoallergenic formula has been shown to improve esophagitis in infants; however, older children and adults may require corticosteroid medication.
Infantile colic and excessive irritability can be symptoms related to allergy in a subgroup of infants. By definition, colic is a condition with increased crying behavior in infants, for which no cause can be found. However, since allergy can potentially lead to inflammation and pain, formula allergy is often considered.
Attempts have been made to associate a variety of other problems with food allergy including joint disease, migraine, and behavioral and developmental disorders such as autism. Causal relationship between food allergy and these disorders remains unproven.
Investigation and treatment of non-IgE-mediated food allergy. The diagnosis rests on the resolution of symptoms and/or biopsy findings on an elimination diet, with a return of symptoms on rechallenge. Unlike the rapid response characteristic of IgE-mediated disease, a prolonged challenge may identify delayed reactions with predominantly gastrointestinal symptoms up to six days after exposure. Elemental diets can be used to eliminate dietary protein antigens completely, then systematic rechallenge of the patient with suspected offending foods. As with IgE food allergies, avoidance of the specific food remains the mainstay of therapy.
There are a number of exciting areas of research into the prevention and treatment of food allergies. Recent reports suggest that the allergic response can be altered by promoting beneficial gut flora ("probiotic therapy"). It has also been discovered that only a few sites (epitopes) on food protein molecules interact with the immune system to create an allergic reaction. Genetic engineering of foods makes it possible to alter these epitopes, creating crops that are "nonallergic." More study is needed to ensure that altering food proteins does not lead to other health concerns or different types of allergy. Other studies are under way to assess the effectiveness of promising new drug therapies for patients with food allergy.
See also Aversion to Food; Baby Food; Health and Disease; Immune System Regulation and Nutrients; Milk, Human; Proteins and Amino Acids.
Justinich, Christopher J. "Food Allergy and Eosinophilic Gastroenteropathy." In Pediatric Gastroenterology, vol. 2, edited by Jeffrey S. Hyams and Robert Wyllie, pp. 33447. Philadelphia: W. B. Saunders, 1999.
Metcalfe, Dean D., H. A. Sampson, and R. A. Simon, eds. Food Allergy: Adverse Reactions to Food and Food Additives. 2d ed, Cambridge, Mass.: Blackwell Science, 1997.
Sampson, H. A. "Food Allergy. Part 2: Diagnosis and Management." Journal of Allergy and Clinical Immunology 103 (1999): 98189.
Sampson, H. A. "Food Allergy. Part 1: Immunopathogenesis and Clinical Disorders." Journal of Allergy and Clinical Immunology 103 (1999): 71728.
Sampson, H. A., and J. A. Anderson. "Classification of Gastrointestinal Disease of Infants and Children due to Adverse Immunologic Reactions to Foods." Journal of Pediatric Gastroenterology and Nutrition 30 (suppl) (2000): 14.
Christopher J. Justinich
Allergy (International Dictionary of Psychoanalysis)
Treatment of allergies became a part of psychosomatics, and subsequently psychoanalysis, following the work of the Chicago School, especially Franz Alexander and Thomas M. French in 1941. Alexander and French focused primarily on asthma rather than cutaneous allergic reactions, but later authors approached these initial studies quite differently. Distancing themselves from the idea of hysterical conversion, they established a link between psychic conflict and analogous somatic conflict. With respect to allergy, they looked for the conflicting elements they considered characteristic. For asthma, these conflicts were primarily conflicts between infants' dependence on their mothers and instinctual demands that threatened this dependence. The crisis itself was associated with an inhibition of emotional expression, especially tears.
Because these factors were not specific, other authors returned to classical methods of analysis. Phyllis Greenacre (1945) insisted that oral sadism can be masked by streams of crocodile tears; here emotional expression assumes renewed importance in an interpretive framework. Jacob Arlow (1955) considered an allergic attack to be a manifestation of transference essentially associated with sadistic fantasies of incorporation. Melitta Sperling (1963) also demonstrated the links between allergies and pregenital factors. Philip C. Wilson (1968) hypothesized that transferential acting may be involved. In the end, the dimension of conversion returned to the foreground. Michel de M'Uzan (1968) insisted on the need to clarify the formation of somatic symptoms, and he turned to the notion of psychosomatic structure.
Pierre Marty reinvigorated the concept of allergies through his description of the allergic character (1976), which followed his account of the allergic object relation fifteen years earlier. He gave the allergic character the following traits: absence or avoidance of aggressiveness, a capacity for identification, absence or avoidance of conflict, considerable merging with the other, and projection as a mode of identification. To describe these traits in turn, absence or avoidance of aggressiveness gives subjects a socially agreeable cast, but is based on a weak capacity for negation, which in turn indicates a weak superego. The capacity for identification was already included in the allergic object relation. Merging with the other (absence of anxiety in the face of the foreign) is also characteristic of certain forms of primary epilepsy and allergic epilepsy, described by Marie-Thérèse Neyraut-Sutterman. Projection, described in 1957, becomes a mode of identification. As a consequence, subjects are unable to project bad objects or to distinguish good from bad.
Only when the allergic child is able, through stranger anxiety, to be afraid do allergic mechanisms begin to diminish. The features above can be found together in a character neurosis (which Pierre Marty referred to as a common allergy bundle), or they can appear as simple, relatively invasive traits that form a more or less split-off component of the personality, manifested only during regression (Pierre Marty referred to these as lateral lines) or deep splitting (parallel lines).
An allergic crisis can be triggered by the overriding of identificatory possibilities, as when the child is presented with two equally invested objects where the identifications have been kept separate. For Pierre Marty, a somatic manifestation is seen as a way station within a regressive movement and not, as in the psychogenetic approach, as the somatic expression of a traumatic situation. For Michel Fain, the unconscious of the typical allergic is the seat of the mother's desire to have the child regress to a primary narcissistic stage of feelings of unity with her, a desire that keeps an entire portion of the ego of the allergic patient in an embryonic state.
For Marty, these properties and variations result in distinct therapeutic indications. In typical cases, the allergic individual is very adaptable, also in the allergic's relation to the analyst and to analysis. The down side of this is that there is a risk of an outbreak of somatic manifestations at the end of treatment. He therefore recommends psychotherapy as a prophylactic, which can help the patient to recognize unconscious factors and become aware of the danger of certain object relations. Marty believes that medical treatment is indicated for somatic disorders, and that analysis and psychotherapy should not be recommended for allergic manifestations.
This conception of an allergic quasi-structure has led to more recent work by Léon Kreisler (1982), Michel Fain (1969), and Gérard Szwec (1993), who have addressed these problems in children.
See also: Allergic object relationship; Asthma.
Alexander, Franz, and French, Thomas M. (1941). Psychogenic factors in bronchial asthma. Washington, DC: National Research Council.
Arlow, Jacob. (1955). Notes on oral symbolism. Psychoanalytic Quarterly, 24, 63-74.
Fain, Michel. (1969). Réflexions sur la structure allergique. Revue française de psychanalyse, 33 (2).
Greenacre, Phyllis. (1945). Pathological weeping. Psychoanalytic Quarterly, 14 62-75.
Kreisler, Léon. (1982). L'économie psychosomatique de l'enfant asthmatique:à propos d'un cas d'asthme grave chez un préadolescent Psychothérapies, 2 (1), 15-24.
Marty, Pierre. (1976). Les mouvements individuels de vie et de mort. Vol. 1: Essai d'économie psychosomatique. Paris: Payot.
M'Uzan, Michel de. (1968). Comment on "Psychosomatic Asthma and Acting Out," by Ph. Wilson. International Journal of Psycho-Analysis, 49 (2-3), 333-335.
Sperling, Melitta. (1963). Fetishism in children. Psychoanalytic Quarterly, 32, 374-392.
Szwec, Gérard. (1993). La psychosomatique de l'enfant asthmatique. Paris: Presses Universitaires de France.
Wilson, C. Philip. (1968). Psychosomatic asthma and acting out: A case of bronchial asthma that developed de novo in the terminal phase. International Journal of Psycho-Analysis, 49 (2-3), 330-333.
Allergies (World of Microbiology and Immunology)
An allergy is an excessive or hypersensitive response of the immune system to harmless substances in the environment. Instead of fighting off a disease-causing foreign substance, the immune system launches a complex series of actions against an irritating substance, referred to as an allergen. The immune response may be accompanied by a number of stressful symptoms, ranging from mild to severe to life threatening. In rare cases, an allergic reaction leads to anaphylactic shock condition characterized by a sudden drop in blood pressure, difficulty in breathing, skin irritation, collapse, and possible death.
The immune system may produce several chemical agents that cause allergic reactions. Some of the main immune system substances responsible for the symptoms of allergy are the histamines that are produced after an exposure to an allergen. Along with other treatments and medicines, the use of antihistamines helps to relieve some of the symptoms of allergy by blocking out histamine receptor sites. The study of allergy medicine includes the identification of the different types of allergy, immunology, and the diagnosis and treatment of allergy.
The most common causes of allergy are pollens that are responsible for seasonal or allergic rhinitis. The popular name for rhinitis, hay fever, a term used since the 1830s, is inaccurate because the condition is not caused by fever and its symptoms do not include fever. Throughout the world during every season, pollens from grasses, trees, and weeds produce allergic reactions like sneezing, runny nose, swollen nasal tissues, headaches, blocked sinuses, and watery, irritated eyes. Of the 46 million allergy sufferers in the United States, about 25 million have rhinitis.
Dust and the house dust mite constitute another major cause of allergies. While the mite itself is too large to be inhaled, its feces are about the size of pollen grains and can lead to allergic rhinitis. Other types of allergy can be traced to the fur of animals and pets, food, drugs, insect bites, and skin contact with chemical substances or odors. In the United States, there are about 12 million people who are allergic to a variety of chemicals. In some cases an allergic reaction to an insect sting or a drug reaction can cause sudden death. Serious asthma attacks are sometimes associated with seasonal rhinitis and other allergies. About nine million people in the United States suffer from asthma.
Some people are allergic to a wide range of allergens, while others are allergic to only a few or none. The reasons for these differences can be found in the makeup of an individual's immune system. The immune system is the body's defense against substances that it recognizes as dangerous to the body. Lymphocytes, a type of white blood cell, fight viruses, bacteria, and other antigens by producing antibodies. When an allergen first enters the body, the lymphocytes produce an antibody called immunoglobulin E (IgE). The IgE antibodies attach to mast cells, large cells that are found in connective tissue and contain histamines along with a number of other chemical substances.
Studies show that allergy sufferers produce an excessive amount of IgE, indicating a hereditary factor for their allergic responses. How individuals adjust over time to allergens in their environments also determines their degree of susceptibility to allergic disorders.
The second time any given allergen enters the body, it becomes attached to the newly formed Y-shaped IgE antibodies. These antibodies, in turn, stimulate the mast cells to discharge its histamines and other anti-allergen substances. There are two types of histamine: H1 and H2. H1 histamines travel to receptor sites located in the nasal passages, respiratory system, and skin, dilating smaller blood vessels and constricting airways. The H2 histamines, which constrict the larger blood vessels, travel to the receptor sites found in the salivary and tear glands and in the stomach's mucosal lining. H2 histamines play a role in stimulating the release of stomach acid, thus contributing to a seasonal stomach ulcer condition.
The simplest form of treatment is the avoidance of the allergic substance, but that is not always possible. In such cases, desensitization to the allergen is sometimes attempted by exposing the patient to slight amounts of the allergen at regular intervals.Antihistamines, which are now prescribed and sold over the counter as a rhinitis remedy, were discovered in the 1940s. There are a number of different antihistamines, and they either inhibit the production of histamine or block them at receptor sites. After the administration of antihistamines, IgE receptor sites on the mast cells are blocked, thereby preventing the release of the histamines that cause the allergic reactions. The allergens are still there, but the body's "protective" actions are suspended for the period of time that the antihistamines are active. Antihistamines also constrict the smaller blood vessels and capillaries, thereby removing excess fluids. Recent research has identified specific receptor sites on the mast cells
Corticosteroids are sometimes prescribed to allergy sufferers as anti-inflammatories. Decongestants can also bring relief, but these can be used for a short time only, since their continued use can set up a rebound effect and intensify the allergic reaction.
See also Antibody and antigen; Antibody-antigen, biochemical and molecular reactions; Antibody formation and kinetics; Antigenic mimicry; Immunology