What are skin tests?

Skin tests may be done to diagnose rashes, moles, skin allergies, bacterial or fungal skin infections, and other diseases. Skin tests are also done to tell the difference between cancer (malignant) cells and noncancer (benign) growths.

What are the most common skin tests?

Allergy testing

Skin tests for allergies include:

• Patch testing. Patch tests are used to help diagnose skin allergies leading to contact dermatitis. Small amounts of substances that may cause an allergic reaction (allergens) are applied to the skin. This is often done on the back using adhesive patches. These are left for a period of time, often 2 days. The skin is then checked for any reaction 2 to 4 days later.

• Prick tests. Allergens are applied to the skin. The skin is pricked so the diluted allergen goes under the skin’s surface.

• Intradermal tests. A small amount of diluted allergen is injected into the skin with a small, thin needle.

Skin biopsy

This test is used to diagnose skin cancer or skin disorders. A skin sample is removed and is checked under a microscope in a lab. Local anesthesia is injected to numb the area. The healthcare provider removes a skin sample with a scalpel or other tool. For a shave biopsy, the provider may use a razor blade. The provider uses a special tool (cylindrical punch) for a punch biopsy. 

Culture

Your provider may remove or scrape skin, hair, or nails. These samples are then grown in the lab to figure out which bacteria, fungi, or viruses may be causing the problem. This is usually a painless, noninvasive test.