Which of the following best describes a patch test?

A patch test is specifically designed to determine whether a person has an allergic reaction to certain products, particularly hair dyes or chemical treatments. During this test, a small amount of the product is applied to a discreet area of the skin, usually behind the ear or on the inside of the elbow. This method allows professionals to observe any potential skin reactions or irritations that could occur as a result of using the product.

When it comes to hair treatments and color products, understanding a client's skin sensitivities is crucial for their safety and comfort. An allergic reaction could lead to serious issues like rashes, blisters, or more severe reactions, which underscores the importance of conducting a patch test before proceeding with more extensive applications.

The other options refer to different aspects of cosmetic services. Testing for hair texture involves assessing the physical properties of the hair strands, while color matching is about finding the right shade to complement the client’s natural hair color. Evaluating product effectiveness is about how well a product performs its intended function, which also does not focus on allergic reactions. These processes, while important, do not specifically identify potential allergic responses like a patch test does.