These include hay fever , eczema , asthma , and many others. Food allergies and drug allergies are common. Allergic reactions can be caused by insect bites , jewelry, cosmetics, and almost any substance that contacts the body. Some people have allergic-type reactions to hot or cold temperatures, sunlight, or other physical stimuli . The mechanism that causes this is not well understood, but it is possible that minute changes in the chemistry of the skin may occur in response to physical stimuli and some component of this chemical change triggers the allergy.
Allergies are common.
There is no known way to prevent allergies. Symptoms may be prevented by avoiding known allergens. Allergies vary according to the type of antigen and the part of the body in which the allergic reaction occurs. History is important in diagnosing allergies, including whether the symptoms vary according to time of day or the season and possible exposures that involve pets, diet changes, or other sources of allergens. Testing may be required to determine if symptoms are an actual allergy or caused by other problems.