What is keratin? Keratin is a fibrous protein found naturally in the hair. It acts as a protective shield against humidity, the primary cause of frizz. Over time, the hair loses keratin from exposure to the sun, the environment, styling and chemical services. Porous spots develop in this damaged hair, much like potholes in a road. Keratin Complex® Smoothing Therapy treatments give the hair shine, strength, smoothness and elasticity.