Why is a patch test required prior to service, and what reaction is tested for?

• A. To check for allergic reaction to dye ingredients (e.g., PPD); tests for redness, itching.
• B. To check hair porosity.
• C. To determine the shade.
• D. To test color fading.

Answer: (B)

A patch test is done before a hair color service to check whether you might have an allergic reaction to the dye ingredients before they contact your scalp. The reaction being looked for is an allergic skin response—redness and itching at the test site, and sometimes swelling or a blistering reaction if sensitive. A small amount of the dye is placed on a discreet area of skin and left in place for about 24 to 48 hours to see if any reaction occurs. If a reaction happens, that indicates sensitivity to the ingredients (such as PPD), and you’d choose a safer alternative or skip the service. Porosity, shade, or fading are not evaluated by a patch test.