The waterproofing protein found in the epidermal cells is called keratin. In addition to its waterproofing properties, keratin toughens the skin and acts as a protective mechanism. When skin is exposed to high degrees of pressure or rubbing, extra keratin is produced within the cells, creating a callus.
Keratin is also a component of hair and nails in humans. Human keratins can be divided into two types: the soft, epithelial keratin of the skin or the hard keratin of the hair. The shedding of keratin cells from the scalp is what results in dandruff flakes.
Certain fungal infections feed on keratin, such as athlete's foot or ringworm.