nail

Last reviewed 10/2023

Nails are keratinized plates derived from skin epidermis. They are situated on the distal, dorsal surface of every digit. The nail, more correctly a nail plate, is made of hard keratin and sits on a nail bed of epidermal cells similar to those of the stratum basale and stratum spinosum.

The nail plate is formed in its proximal region, termed the root. Here, within a protective nail fold of skin below the interface with epidermal cells - the eponychium or cuticle, a matrix of germinative epidermal cells divide and keratinize. The matrix extends as far forward as the lunula, the crescent-shaped area that is whiter than the distal body of the nail due to incomplete keratinization.

Keratinized cells distal to the matrix are pushed forward, sliding over the nail bed, by the division of cells at the root. The nail is bounded on either side by margins of skin termed nail walls. Distally, the epidermis adheres to the undersurface of the free nail edge; this area is termed the hyponychium.

Nails function to:

• reinforce and protect the terminal phalanx
• aid in the sensation of fine touch