Explain why a person becomes flushed when he or she has a fever.
A fever is a response by the immune system to help the body fight an infection. Raising the body temperature can cause bacteria and viruses to not be able to replicate as quickly and allow the immune system to gain an advantage in the fight.
Flushing during a fever is part of the skin's role in the thermoregulation of the body. Blood carries a lot of things to all parts of the body, including oxygen, nutrients, wastes, and in the case of flushing, heat. Blood vessels dilate and constrict in response to a raising or lowering of body temperature. When the body temperature decreases below our 'set point' of 98.6, capillaries in our extremities will constrict so that more blood, and thus heat, stays closer to our chest and abdomen. This reduces the amount of heat lost and helps to maintain a consistent temperature next to the most vital parts of our bodies.
When body temperature increases, as during a fever, blood vessels in our extremities including our face dilate. This allows more blood flow close to the skin, and extra heat can escape helping to reduce body temperature and maintain homeostasis. Even though a fever may be happening, this flushing can help keep the fever from reaching very dangerous levels.
Fevers can occur for many reasons. A fever is a physiological response to invading pathogens such as viruses or bacteria that can make a person sick, or to certain diseases and medical conditions. The increase in temperature may help kill the pathogen, but it can be dangerous for the person experiencing the fever as well.
This is where flushing comes in. It is a mechanism to counter the rise in body temperature by getting rid of the extra heat produced by the fever. When a person flushes, the capillaries close to the surface of the skin fill with blood and the heat from this blood is able to diffuse into the surroundings, thus cooling the body. All this blood at the skin's surface gives the person a flushed appearance.
Fevers are caused by the body's immune response to a pathogen. The body raises its own internal temperature to a level that should not cause permanent damage to its own cells but that may kill the disease causing agent (such as a virus or bacteria).
To understand why having a fever may cause someone to become flushed, we need to first understand how the circulatory system is involved in thermoregulation, the process by which the body maintains a stable internal temperature. As blood flows throughout the body, carrying oxygen and nutrients to various tissues, it can also carry heat. The center of the body, in the chest and abdomen, is the warmest and most stable in terms of temperature, with the extremities and areas close to the skin being more prone to fluctuations in temperature. When blood flows through warmer parts of the body it is heated, and when it flows closer to the external environment it loses heat.
When the internal temperature is too low, the body tries to minimize the heat lost from the blood by directing flow away from the skin and extremities. It does this by constricting blood vessels in these areas (known as vasoconstriction). This explains why when you're very cold, your fingers and toes may look pale and feel numb. When the body becomes too warm, the opposite happens- blood is directed away from the warm, internal areas into the extremities and skin. This increase in blood to the thin capillaries of the face causes the capillaries to swell or dilate (this is known as vasodilation) as blood passes through and is cooled by proximity to the external air. This swelling of the capillaries with blood makes the skin appear red, causing what we call "flushing."
So, why does a fever cause a person to flush?
Blood rushes to the skin as part of the body's reaction to an increase in internal temperature, an attempt to maintain a stable internal environment.
A face becomes flushed when the capillaries in the body dilate as blood flows through them in an effort to dissipate the excess heat generated by means of the skin's surface. Flushing is the body's way of maintaining homeostasis in response to the virus causing the fever.