A skin prick test is a simple and painless procedure undertaken to find out which substances (allergens) cause allergic reactions in an affected person. Dilute solutions are made from extracts of allergens, such as pollen, dust, dander, and food, that commonly cause allergic reactions.
A drop of each solution is placed on the skin, which is then pricked with a needle. The skin is observed for a reaction, which usually occurs within 30 minutes of applying the solution. Antihistamines should not be taken on the day of the test because they may prevent any reaction.
Drops from 8–10 solutions containing different allergens are placed on the skin. The skin underneath is then pricked with a needle and observed for a reaction.
If a person is allergic to one of the substances applied to the skin, a red lump, indicating a positive reaction, appears at the site of the needle prick.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.