Lysine

Lysine is an essential amino acid that the body cannot synthesize on its own and must obtain through diet or topical application. It is used in cosmetic and personal care formulations including serums, masks, cleansers, and conditioners. As an amino acid, it serves as a building block for proteins such as collagen. The source page lists it as an ingredient across a wide range of product types including anti-aging serums, micellar waters, and hair care products.