Which method is commonly used to determine a client's hair type?

Assessing hair thickness and texture is a fundamental method for determining a client's hair type because it provides direct insight into the individual characteristics of the hair. Hair type can vary widely among individuals, categorized usually into texture (which can be straight, wavy, curly, or coily) and thickness (fine, medium, or coarse). This information is essential for cosmetologists to recommend suitable hair products, treatments, and styling techniques that align with the client's specific needs.

The other methods mentioned, though useful in specific contexts, do not effectively identify hair type on their own. A skin patch test is primarily used to check for allergic reactions to products rather than determining hair characteristics. Reviewing past hair treatments can provide context about what might have been done to the hair previously but does not define its inherent qualities. Consulting product reviews, while helpful for understanding the performance of products others have tried, does not offer any information on the unique hair type of the client in question.