When coloring mustaches, what should never be used?

In the context of coloring mustaches, aniline derivatives are substances that can pose health risks due to their potential for skin irritation and allergic reactions. These compounds are known for their use in hair dyes and other cosmetic products, but they are not recommended for facial hair, particularly mustaches, due to the sensitivity of the skin in that area.

Using aniline derivatives can lead to adverse effects, such as inflammation or more severe allergic reactions, which can create discomfort for the client. The facial area is typically more absorbent than other parts of the body, increasing the risk associated with using products that contain these derivatives.

In contrast, oxidizing agents, ammonia-based dyes, and semipermanent colors may all serve appropriate purposes in hair coloring. While they can also have side effects or may not be suitable for everyone, the specific concern with aniline derivatives highlights their potential for significant reactions on facial skin. This is why they should be avoided when it comes to coloring mustaches.