Keratin is a basic fibre protein consisting of 18 amino acids, of which our hair, nails and skin are made up.A keratin deficiency can manifest itself in brittle hair, damaged cuticles or cracking of the nail plate.There are several ways to supplement keratin. The most important distinction to be made is between internal and external methods. There is a large range of keratin hydrolysate supplements available on the market. The supplements are designed to be ingested - these are usually tablets or capsules.