Keratin is a tough fibrous protein that strengthens skin, hair and nails with its tight strands and intertwined structures. There are two types of keratin, according to Bio-Medicine.org: alpha-keratin, which is abundant in humans and mammals, and beta-keratin that is primarily in birds and reptiles.

Keratin is a major component responsible for strengthening the hair, making it less likely to break.

Keratin helps to smooth and coat frizzy and frayed hair shafts, resulting in smoother and straighter hair. It repairs damaged hair by smoothing and coating the hair shafts and helps to keep in moisture.

Keratin is also contained in the outer epidermis and creates the tough skin in calluses. It helps skin maintain its elasticity and firmness. Keratin controls cell growth and renewal, which helps to soften and control wrinkles.

Keratin has an influence on melanin and skin pigmentation. The protein plays a part in waterproofing skin, according to NaturalSkinHealth.com. It also creates a slight barrier against bacteria and other organisms.

Nails are made up of keratin, which causes them to become less prone to chipping and breaking. Keratin is a major part of hardened structures of animals such as horns, hoofs, beaks and even feathers.

Keratin is such a good coating that pharmacies use this same protein for the smooth coating on pills.