A salon professional should never use an ammonium thioglycolate product on a client's hair if it has been previously treated with:

Ammonium thioglycolate is a chemical commonly used in perming and hair straightening treatments. Its efficacy and safety can be significantly affected by the presence of certain other chemical processes or products applied to the hair.

When hair has previously been treated with sodium hydroxide, a strong alkaline chemical often used in relaxers, the hair's structure can be compromised. Sodium hydroxide and ammonium thioglycolate have different pH levels and can interact negatively when used together, leading to significant damage, including excessive breakage or weakening of the hair. This is primarily because both chemicals alter the disulfide bonds in hair, but doing so in incompatible ways can severely compromise the hair's integrity.

The other options—hydrogen peroxide, dimethicone, and cetearyl alcohol—do not have the same level of contraindication with ammonium thioglycolate. Hydrogen peroxide, while a potent chemical, is generally used for color lifting and bleaching, and while it can affect hair health, it does not react negatively with ammonium thioglycolate to the same dangerous degree as sodium hydroxide. Dimethicone is a silicone-based ingredient commonly found in hair products that acts as a conditioning agent, and cetearyl alcohol is a fatty