Prick test – It detects immediate (type I) hypersensitivity. Commercially prepared diluted antigens and a control are placed as single drops on marked areas of the forearm. The skin is pricked through the drops using separate sterile fine needles. The drops are removed with tissue wipe. After 10 minutes the sites are inspected and the diameter of any wheal measured and recorded. A result is considered positive if the test antigen causes a wheal of 4 mm or greater. Conditions under investigations are usually urticarial or atopic dermatitis.

Patch test – Detecting the allergens responsible for allergic dermatitis. A patch test involves applying a chemical to the skin and then watching for dermatitis to develop 48-96 h later. The test materials are applied to the back under patches (the occlusion encourage penetration of the allergen). The patches are left in place for 48 h, then removed and inspected 10 min later, and again 2 days later. The test detects type IV delayed hypersensitivity reactions. Positive test doesn’t prove allergen has caused episode of contact dermatitis.