A hard, curved plate on the fingers and toes composed of keratin (a tough protein). Nails grow from an area called the nail bed. At the base of each nail a half-moon shape, the lunula, is crossed by a flap of skin called the cuticle. The surrounding skin is known as the nail fold. A fingernail takes about 6 months to grow from base to tip; toenails take twice as long. The nails are susceptible to damage through injury, or by bacterial or fungal infections, especially tinea and candidiasis. Sometimes they become abnormally thick and curved: a condition known as onychogryphosis. Nail abnormalities may be a sign of skin disease, such as alopecia areata, psoriasis, and lichen planus, or of more generalized disease, for example iron-deficiency anaemia. Unusual nail colour may indicate disease. Treatment of nail disorders can be difficult. Creams and lotions seldom penetrate sufficiently; oral medication may take months to be effective.
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