Allergy skin tests are done by the percutaneous or `prick' method, using various scarifiers, to identify allergies causing "atopic" disease, such as rhinitis, rhino-conjunctivitis (involving the nose and eyes, as in "hay fever" or "seasonal allergies"or allergy to various pollens, or similar symptoms caused by cats, dogs, house dust mites, etc.), allergic asthma, sinusitis, certain types of urticaria (hives), food allergies, stinging-insect allergies, allergy to penicillin, local anesthetics and to latex.

Intradermal injections are also used if the prick tests are negative.

Tests are read in 15-20 minutes and described as being slightly, moderately, or markedly positive in various ways, by using +, ++, +++, ++++, +++++ or by measuring the size of the papule and surrounding erythema (redness) in millimeters.

Allergy tests can also be done by the RAST method ("radioallergosorbent test") a blood test that can measure the specific IgE antibody to various allergens. As with the skin tests, this test can be used for similar allergens. Recently, Pharmacia Diagnostics has introduced the CAP system, which replaces the RAST and in the case of food allergens, it could predict clinical reactivity with greater than 95% certainty. (see "Methods of evaluation of atopy" by Dr. Barry Zimmerman).

Patch tests are done by the application of allergens on the skin (back usually) using special adhesive materials to identify causes of contact dermatitis. Results are read 24-48 hours after applying the patches. This type of allergy, contrary to the 'atopic' immediate type, is a delayed form of allergy. The allergens involved are cosmetics, metal, perfumes, preservatives, etc. and tests often done by dermatologists.

The photo below is of a test done by an ice cube and showing a strongly positive reaction, after application of one minute.