Keratin is one of a family of fibrous structural proteins. Keratin is the protein that protects epithelial cells from damage or stress. It is the key structural material making up the outer layer of human skin. Keratin treatments fill in the porosity of your hair, as overly-porous hair causes tangles, frizz, and breakage," Sprinkle explains. "Your hair is made up of keratin, so the treatment is putting the protein back into the hair, which is often lost due to age and chemical services.. This treatment doesn't straighten hair (it does loosen curl just a little bit), it just smoothes down frizz and decreases dry time.