Which of the following products is prohibited in cosmetology salons or schools?

Methyl methacrylate liquid monomers, often referred to as MMA, are prohibited in cosmetology salons and schools due to their safety risks. These substances can cause severe allergic reactions, skin irritation, and other negative health effects for both clients and practitioners. MMA is considered too hazardous for use in nail enhancements or other cosmetic procedures, which is why regulations specifically ban its use in professional environments.

In contrast, isopropyl alcohol, hydrogen peroxide, and glycolic acid are commonly used in various beauty treatments and salon practices under appropriate safety guidelines. They have established applications in disinfecting, cleansing, and skin treatments, and they are regulated for safe use in these contexts. Therefore, they are permissible within the standards set by cosmetology regulations.