Allergy

An allergy is an exaggerated immune response where the body mistakenly identifies an ordinarily harmless allergen as a threat. Allergic reactions give rise to allergic diseases such as hay fever, allergic conjunctivitis, allergic asthma, atopic dermatitis, food allergies, and anaphylaxis. Symptoms of allergic diseases may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling. Common allergens include pollen, certain foods, metals, insect stings, medications, and materials, such as latex. The development of allergies is due to genetic and environmental factors. The mechanism of allergic reactions involves immunoglobulin E antibodies (IgE) binding to an allergen and then to a receptor on mast cells or basophils, where they trigger the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person's medical history. Further testing of the skin or blood may be useful in certain cases. Positive tests, however, may not necessarily mean there is a significant allergy to the substance in question. Early exposure of children to potential allergens may be protective. Treatments for allergies include avoidance of known allergens and the use of medications such as steroids and antihistamines. In severe reactions, injectable adrenaline (epinephrine) is recommended. 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. Its use in food allergies is unclear. Allergies are common. In the developed world, about 20% of people are affected by allergic rhinitis, food allergy affects 10% of adults and 8% of children, and about 20% have or have had atopic dermatitis at some point in time. Depending on the country, about 1–18% of people have asthma. Anaphylaxis occurs in between 0.05–2% of people. Rates of many allergic diseases appear to be increasing. The...