This is a test done on the skin to identify the allergic substance (the allergen) that is the trigger for an allergic reaction.
A small amount of the suspected allergy-provoking substance (the allergen) is placed on the skin of the forearm or back. The skin is then gently punctured through the small drop with a special sterile puncture device.
If the skin reddens and, more importantly, if it swells, then the test is read as positive. If there is no reaction, it is read as negative.
If the skin test is positive, it implies that the patient has a type of antibody (IgE antibody) on specialized cells in the skin that release histamine to cause redness and itching. (These cells are called mast cells and the IgE antibody bound to them is specific to the allergic substance.
An allergy skin test is also called a pric/puncture test. The older terminology was “scratch test.”
Skin tests are rapid, simple, and relatively safe. They can be very helpful in specifically identifying causes of allergies.
In some extremely allergic patients who have severe reactions called anaphylactic reactions, skin testing cannot be used because it could evoke a dangerous reaction. Skin testing also cannot be done on patients with extensive eczema.