Which hair color product does not require a patch test?

Semi-permanent hair color products do not typically require a patch test before use. This is largely due to the fact that they contain fewer harsh chemicals compared to permanent hair color products. Semi-permanent colors usually deposit color on the hair shaft without altering the hair's natural structure significantly. Therefore, they are known for being less irritating to the scalp and skin, making a patch test unnecessary in most situations.

In contrast, permanent hair color often includes stronger chemicals, like ammonia or peroxide, that can cause allergic reactions in individuals with sensitive skin. Lightening products, which can also be quite harsh, similarly warrant a patch test for the same reasons. Temporary hair color, while generally less aggressive, can still cause reactions for some individuals, particularly if used frequently, thus necessitating a patch test as a precaution.