An allergy is an abnormal reaction by a person’s immune system against particular substance. Most things that cause allergies are not harmful, and have no affect on people who are not allergic. Allergic reactions occur to environmental substances known as allergens; these reactions are acquired, predictable and rapid.
In the most common type of allergy, at the first exposure to an allergen, the immune system releases histamine and other chemicals to defend against the allergens. It is the release of these chemicals that cause allergic reactions, as the body attempts to rid itself of the invading allergen.
Some of the most common allergies include those to food and to airborne allergens such as pollen, mold, dust mites, animal fur and much more. The type and severity of allergy symptoms vary from child to child. Airborne allergens can cause itchy nose or throat, sneezing, coughing, and nasal congestion.