The horny zone of the nail is composed of hard-keratin and has a distal exposed part (body) and a proximal hidden portion (root). The root is covered by a distalward prolongation of the stratum corneum of the skin. This narrow fold is composed of soft-keratin and is termed the eponychium. Distal to the eponychium is the lunula, a part of the horny zone that is opaque to the underlying capillaries.

Deep to the distal or free border of the nail, the horny zone of the fingertip is thickened and is termed the hyponychium. The horny zone of the nail is attached to the underlying nail bed. The matrix (proximal part of the bed) produces hard-keratin. The bed may also generate nail substance.

The nails are hardenings of the horny zone of the epidermis. They overlie the dorsal aspect of the distal phalanges. They protect the sensitive tips of the digits and serve in scratching. The growth of the nail is affected by nutrition, hormones, and disease. Nail growth involves considerable protein synthesis. White spots indicate incomplete keratinization.