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The term allergy is used to describe a response, within the body, to a substance, which is not necessarily harmful in itself, but results in an immune response and a reaction that causes symptoms and disease in a predisposed person, which in turn can cause inconvenience, or a great deal of misery. An allergy is everything from a runny nose, itchy eyes and palate to skin rash.
Allergy is widespread and affects approximately one in four of the population in the UK at some time in their lives. Each year the numbers are increasing by 5% with as many as half of all those affected being children.
Allergic reactions are caused by substances in the environment known as allergens. Almost anything can be an allergen for someone. Allergens contain an organic molecule, protein.
The most common allergens are pollen from trees and grasses, house dust mite, moulds, pets such as cats and dogs, insects like wasps and bees, industrial and household chemicals, medicines, and foods such as milk and eggs. Less common allergens include nuts, fruit and latex. There are some non-protein allergens which include drugs such as penicillin. For these to cause an allergic response they need to be bound to a protein once they are in the body.
An allergic person's immune system believes allergens to be damaging and so produces a special type of antibody (IgE) to attack the invading material. This leads other blood cells to release further chemicals (including histamine) which together cause the symptoms of an allergic reaction.
Source; Allergy UK
Main allergies include asthma, allergic rhinitis (nasal allergies), conjunctivitis, eczema, anaphylaxis, hives.