A nail is a horn-like keratinous envelope covering the tips of the fingers and toes in most primates. Nails evolved from claws found in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin which is found in the hooves, hair, claws, and horns of vertebrates.

The growing part of the nail is under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail. In humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow up to four times faster than toenails.

Fingernails require three to six months to regrow completely, and toenails require twelve to eighteen months. The actual growth rate is dependent upon age, sex, season, exercise level, diet, and hereditary factors. The longest female nails are 601.9 cm long, an average of 60.19 cm (23.7 inches) for each fingernail.

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