Nail

A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most primates, and a few other mammals.

Nails are similar to claws, which are found on numerous other animals. In common usage, the word nail often refers to the nail plate only.

Fingernails and toenails are made of a tough protein called keratin, as are animals' hooves and horns. Along with hair they are an appendage of the skin.

The nail consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it.

The growing part of the nail is the part still under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail.

In mammals, the length and growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). Thus, in humans, the nail of the index finger grow faster than that of the little finger; and fingernails grow up to four times faster than toenails.

In humans, nails grow at an average rate of 3 mm (0.12 in) a month (as they are a form of hair). Fingernails require 3 to 6 months to regrow completely, and toenails require 12 to 18 months. Actual growth rate is dependent upon age, gender, season, exercise level, diet, and hereditary factors. Nails grow faster in the summer than in any other season. Contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and tightens, making the nails (and hair) appear to grow.