Keratin is a type of protein that makes up your skin, hair and nails. Keratin is the structural block of your hair. As we age, we are prone to a decline in the production of Keratin. This makes your hair susceptible to dryness and breakage. Biting your nails aren't the only things that put them at risk. When you lose Keratin in the natural process (a natural part of ageing) this can cause your nails to become brittle. Keratin is a protective protein which is why it is less prone to tearing, which is why strong and flexible fibers make your skin strong against tearing. Again, as part of the normal aging process, Keratin production decreases which is what can result in dry and dull skin.