What is the main purpose of a patch test?

• A. To check for allergic reaction to dye ingredients (e.g., PPD); tests for redness, itching.
• B. To gauge porosity.
• C. To measure strength of color.
• D. To determine the exact shade.

Answer: (A)

A patch test is used to screen for an allergic reaction to hair dye ingredients like PPD before applying color. By applying a tiny amount of the dye mixture to the skin and watching for signs such as redness, itching, or swelling over 24 to 48 hours, you can determine if the product could cause a reaction on the scalp. This safety check helps prevent a potential allergic reaction during a full color treatment.

Other options don’t fit because porosity testing assesses how well hair takes in moisture and color, not whether you’re allergic to ingredients. Measuring the strength of color and determining the exact shade are about how the dye will look on hair, not whether you’ll react to it on skin.