The role of keratin is mainly related to its structural characteristics, which contain many polypeptide chains, thus making keratin insoluble or slightly soluble in water, so it is a protein with a protective effect. In addition, keratin contains more cystine, which is rich in disulfide bonds, which determines the chemical stability of keratin and its high mechanical strength. Therefore, the main role of keratin has a strong anti-drawing property and plays a major protective role in the organism. The human hair and nails are made of keratin. Although the appearance of hair and nails are very different, they are both composed of keratin.