Allergy scratch test: Test done on the skin to identify the allergy substance (the allergen) that is the trigger for an allergic reaction.

A small amount of the suspected allergy-provoking substance is placed on the skin. The skin is then gently scratched through the small drop with a special sterile needle.

If the skin reddens and, more importantly, if it swells, then the test is read as positive and allergy to that substance is considered probable.