To prevent allergic reaction to hair color, which test should be administered?

• A. Patch test
• B. Scalp test
• C. Allergy panel
• D. Blood test

Answer: (A)

Patch testing is used to prevent allergic reactions to hair color by checking how a client’s skin will react to the dye ingredients before full application. A small amount of the dye (often including the common allergen PPD) is placed on a patch of skin, usually behind the ear or on the inner forearm, and left in place for about 24 to 48 hours. After removal, you look for redness, itching, swelling, or a rash. If a reaction appears, it signals a potential allergy to the product, and you can choose a different formulation or skip that dye to avoid a severe reaction.

This method is preferred because it directly tests the individual’s skin sensitivity to the specific cosmetic ingredients. A scalp test isn’t the standard for screening and can be impractical or less reliable. Blood tests or broad allergy panels don’t accurately predict contact reactions to hair dyes, since those tests are not tailored to cosmetic ingredients.