Allergy

Common allergens include pollen and certain foods.^[11] Metals and other substances may also cause such problems.^[11] Food, insect stings, and medications are common causes of severe reactions.^[2] Their development is due to both genetic and environmental factors.^[2] The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.^[13] Diagnosis is typically based on a person's medical history.^[3] Further testing of the skin or blood may be useful in certain cases.^[3] Positive tests, however, may not necessarily mean there is a significant allergy to the substance in question.^[14]


Early exposure of children to potential allergens may be protective.^[5] Treatments for allergies include avoidance of known allergens and the use of medications such as steroids and antihistamines.^[6] In severe reactions, injectable adrenaline (epinephrine) is recommended.^[7] Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites.^[6] Its use in food allergies is unclear.^[6]


Allergies are common.^[10] In the developed world, about 20% of people are affected by allergic rhinitis,^[15] about 6% of people have at least one food allergy,^[3][5] and about 20% have or have had atopic dermatitis at some point in time.^[16] Depending on the country, about 1–18% of people have asthma.^[17][18] Anaphylaxis occurs in between 0.05–2% of people.^[19] Rates of many allergic diseases appear to be increasing.^[7][20][21] The word "allergy" was first used by Clemens von Pirquet in 1906.^[2]