Which type of shampoo is designed to neutralize unwanted residues in hair?

Neutralizing shampoo is specifically formulated to counteract any unwanted residues present in the hair, particularly those that may be left behind by chemical treatments or styling products. It works by adjusting the pH level of the hair back to its natural state, helping to remove buildup that can cause the hair to appear dull and lifeless. This type of shampoo is often used after certain chemical processes, such as perming or relaxing, to help remove alkaline residues and maintain hair health.

The other types of shampoos mentioned serve different purposes. Deep-conditioning shampoo aims to provide moisture and nourishment to dry or damaged hair without necessarily addressing residue buildup. Sulfate-free shampoo is designed to cleanse hair gently without stripping natural oils but does not specifically target residues. Color-enhancing shampoo focuses on maintaining or enhancing hair color by depositing color pigments, rather than neutralizing residues. Therefore, the specific formulation and function of neutralizing shampoo make it the correct choice for this question.