Keratin

Keratin is a family of strong, fibrous proteins that form the main structural component of the hair shaft, as well as the outer layers of skin and nails. In hair, keratin molecules assemble into long chains and are held together by disulfide and hydrogen bonds; this organized structure creates the cortex and cuticle layers that determine hair strength, elasticity, and texture.

Chemical treatments, heat styling, and environmental exposure can break keratin bonds and damage the cuticle, causing hair to become weak, brittle, or frizzy. Rebuilding or protecting keratin with protein-based conditioners, protective styling, and professional smoothing treatments can improve appearance and manageability, and clinicians may consider keratin integrity when assessing hair fragility or planning treatment for hair and scalp conditions.