Which term refers to a chemical mixture that penetrates the hair's cuticle layer?

The term that describes a chemical mixture capable of penetrating the hair's cuticle layer is deep-conditioning treatment. This type of treatment is designed to provide intense moisture and nourishment to the hair shafts, making it especially beneficial for dry or damaged hair. Deep-conditioning treatments often contain a variety of conditioning agents, oils, and proteins that work to restore hydration and improve the overall structure of the hair by reaching deeper layers than regular conditioners.

In contrast, the other choices serve different purposes. Scalp astringent lotions are typically designed to address scalp issues by removing excess oil or product buildup rather than conditioning the hair itself. Neutralizing shampoos are used mainly in the hair coloring process to restore the natural pH balance to the hair after it has been chemically treated. Humectants, while they help attract moisture, do not specifically describe a treatment that penetrates the hair cuticle like deep-conditioning treatments do. These agents are more focused on retaining moisture rather than nourishing the hair internally.