What are skin tests?

Skin tests may be done to diagnose rashes, moles, skin allergies, bacterial or fungal skin infections, and other conditions and 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 48 to 96 hours. The skin is then checked for any reaction 2 to 4 days later.

• Prick or scratch tests. Allergens are applied to the skin. The skin is pricked or scratched 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. Your doctor removes a skin sample with a scalpel or other tool. For a shave biopsy, your doctor may use a razor blade. A special tool (cylindrical punch) is used for a punch biopsy.

Culture

Your doctor 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.