According to research done at Penn State University, the perception of fear is not as simple as just smelling it. Nancy Diehl, an equine specialist, states that there are two distinct olfactory systems: one which is a main one, and one less direct. The main olfactory system is involved with the direct recognition of smells, depending on the nose's ability to detect volatile, airborne molecules; for example, on entering grandmother's house, we immediately recognize the smell of apple pie. But, since emotional systems, such as fear, are not capable of generating such scent-laden molecules, Diehl contends that animals cannot "smell fear."
In the other system, which is called the accessory olfactory system, communication begins with the vomeronasal organ, which is located above the soft palate of the mouth, on the floor of the nasal cavity. Highly specific smell molecules are transmitted to the accessory olfactory bulb where they are collected and processed. Then, nerves from the accessory and main olfactory bulbs project to the limbic system. the part of the brain that deals with emotional perception and response.
So, instead of directly sensing or smelling fear, the accessory olfactory system "reads" the messages of non-volatile phenomenes communicative chemicals emitted by all animals. Research suggests that phenomenes molecules transmit information concerning territory, aggression, and most prominently, reproduction. The fact that the limbic system is responsible for the processing of smells offers another clue, as one of the limbic system's primary organs, the amyglada, is directly responsible for receiving and responding to fear.
However, Diehl also states that this processing can only occur among members of the same species. So, the dog still does not really smell fear in a person, although he can, indirectly, detect this in another dog. Instead, animals interpret the apprehension in a person through the behavioral clues that a person communicates, such as hesitancy to approach the animal and other erratic movements. Through operant conditioning, having experienced such hesitancy and erratic behaviors from other people, the animal, then, quickly recognizes his/her fear.
According to U.S. researchers,sweat produced by the body when it’s awestruck launches those signals that are sighted nearby and begin to have the same reaction.
Even those who are normally confident have sometimes moments of uncertainty. To find out if fear can be "smelled" of those around a scared person, researchers from Stony Brook University in New York have taken samples of sweat from the 40 volunteers who were preparing to jump from a plane, for the first time. Other participants in the study had to smell these samples of individuals who weren't scared , while they were brain monitored . When sweat coming from the scared ones was detected , certain areas of the brain involved in producing state of fear were activated.