Allergic people tend to have itchy skin more than nonallergic people. But that’s not too surprising; the skin is the largest organ in the body, so it's logical that is suffers a fair amount of allergic discomfort.

As with other allergic reactions, the chemical histamine is primarily at fault. Allergens prompt the release of histamine from skin cells; it irritates nearby nerve endings; they send a message to the brain that there’s a problem; and the brain wires back the sensations that you feel – the discomfort, the compulsion to scratch, the itch.

Most allergic itching is caused by drugs, insect stings or bites, or contact with allergens such as makeup, poison ivy or nickel jewelry. It's not very often that food and inhalant allergies trigger a case of itching. Although you can react to pollen that gets on your skin or from handling foods to which you’re allergic.

Itching, of course, has many other causes besides allergens: rough clothing, dry skin, air conditioning or cold weather, and a number of disease. Rule out these other possibilities before you investigate allergy. If you’re fairly certain that an allergen is the problem, you can soothe the itch by applying cool, wet compresses and avoiding the allergen.

Don’t Overlook Drugs As A Cause, What to Do about Insect Allergies, and Contact (Skin) Allergies, give specific advice for dealing with various causes of allergic itching (see the entries on Hay Fever, Hives, and Skin Inflammation (Atopic Dermatitis and Eczema)). If you pursue all those possibilities and still itch, consult Other Unexpected Allergies. Your itching may be a one in a million reaction to a substance that almost never acts as an allergen.