What type of substance is referred to as depilatories, commonly used to remove hair at the skin level?

Depilatories are substances specifically formulated to remove hair from the skin's surface through a chemical process, typically involving the use of alkali substances. These substances work by breaking down the protein structure of the hair, making it easier to wipe away. The reason alkali substances are effective as depilatories is that they can alter the hair's keratin structure, allowing for smooth hair removal.

Other options such as shampoos, wax, and lotions do not serve the same function. Shampoos are designed for cleansing hair on the scalp rather than removing hair from the skin. Wax requires a different technique for hair removal, involving the physical pulling of hair from the follicle rather than a chemical breakdown. Lotions might be used for various skin care purposes but do not have the targeted action necessary for hair removal as depilatories do. Therefore, the identification of alkali substances as depilatories is accurate and reflects their role in hair removal practices.