Allergy

Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[11] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[1] Symptoms may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling.[12] Note that food intolerances and food poisoning are separate conditions.[3][4]

Quick facts: Allergy, Specialty, Symptoms, Types, Causes... ▼

Allergy
Hives are a common allergic symptom.
Specialty	Immunology
Symptoms	Red eyes, itchy rash, vomiting, runny nose, shortness of breath, swelling, sneezing, and cough.
Types	Hay fever, food allergies, atopic dermatitis, allergic asthma, anaphylaxis[1]
Causes	Genetic and environmental factors[2]
Diagnostic method	Based on symptoms, skin prick test, blood test[3]
Differential diagnosis	Food intolerances, food poisoning[4]
Prevention	Early exposure to potential allergens[5]
Treatment	Avoiding known allergens, medications, allergen immunotherapy[6]
Medication	Steroids, antihistamines, epinephrine, mast cell stabilizers, antileukotrienes[6][7][8][9]
Frequency	Common[10]

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]