Hundreds or even thousands of ordinary substances can trigger allergic reactions. These are called "allergens." Among the most common are plant pollens, molds, household dust (dust mites), animal dander, industrial chemicals, foods, medicines and insect stings. An allergic reaction may occur anywhere in the body, but usually appears in the skin, eyes, lining of the stomach, nose, sinuses, throat and lungs -- places where special immune system cells are stationed to fight off invaders that are inhaled, swallowed or come in contact with the skin.

Allergies can affect anyone, regardless of age, gender, race or socioeconomic status. While it's true that allergies are more common in children, they can occur for the first time at any age or, in some cases, recur after many years of remission. Although the exact genetic factors are not yet understood, the tendency to allergies, as well as to allergic disease, is linked to heredity.

The best first step in the diagnosis of allergies is a thorough health history and physical examination. If you have allergy symptoms that occur in association with exposure to certain things, that is highly significant. Allergy treatment in Kolkata or diagnostic tests, such as skin tests or blood tests, provide similar information and merely confirm what your health history tells the doctor. If your doctor were to rely exclusively on the results of skin or blood tests (without history and physical examination), you could be diagnosed as having an allergic problem that you don't necessarily have. Skin tests, in most situations, are preferable because (1) the results are available immediately, (2) they are less expensive and (3) they are more sensitive to subtle allergies. A blood test is appropriate in certain situations, particularly when you (1) cannot suspend antihistamine therapy which can inhibit skin tests, (2) have widespread skin disease making skin testing difficult, (3) are so sensitive to the allergen that the test might be risky or (4) cannot be skin tested for some other reason.