Which of the following best describes a skin patch test?

A skin patch test is primarily conducted to determine how well the skin tolerates specific products, particularly those that contain chemicals that could potentially cause an allergic reaction or irritation. This procedure involves applying a small amount of the product to a discreet area of the skin and monitoring for any adverse reactions, such as redness, swelling, or itching. This is crucial in the barbering and cosmetology fields to prevent harmful effects and ensure client safety.

The other options do not accurately represent the purpose of a skin patch test. Testing for hair color matching involves different techniques, while estimating hair length pertains to cutting and styling practices rather than skincare. Similarly, assessing styling techniques focuses on the stylist's skill rather than individual skin sensitivities. Consequently, option B stands out as the most appropriate description of a skin patch test within the context of product safety and client care.