What might a cosmetologist use to determine skin allergies?

A cosmetologist uses a patch test to determine skin allergies because this method involves applying a small amount of a substance to a patch that is then placed on the skin, typically on the back. This allows professionals to observe how the skin reacts to specific allergens over a period of time, usually 48 to 72 hours. If an allergic reaction occurs, such as redness, itching, or swelling, it indicates a sensitivity to that substance.

The patch test is specifically designed to identify contact allergens and is the most reliable method for assessing reactions, making it essential for ensuring client safety and tailoring appropriate skin care treatments. Other methods like the color test, heat test, and strain test do not adequately measure skin allergies or sensitivity in the same systematic way as a patch test.