Keratin is the type of protein that makes up your hair, skin, and nails. People who use keratin on their hair report that their hair is smoother and easier to manage. The effects vary greatly depending on whether your hair is healthy to begin with, what the natural thickness of your hair is, and what kind of keratin treatment you use.

Keratin works by smoothing down the cells that overlap to form your hair strands. The layers of cells, called the hair cuticle, theoretically absorb the keratin, resulting in hair that looks full and glossy. Keratin also claims to make curly hair less frizzy, easier to style, and straighter in appearance.