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The keratin nail plate plus the matrix, bed, and folds that grow it; protects fingertips and aids fine touch and grip.
Medically reviewed & updated
The nail unit is the specialized structure at the tips of fingers and toes that produces and supports the hard nail. Nails are made of tightly packed, keratinized cells and serve to protect the sensitive fingertips, enhance fine touch, and help with grasping, scratching, and manipulating small objects. The nail unit includes the nail plate, nail matrix, nail bed, cuticle, and the surrounding skin folds.
The nail plate is the visible, rigid part of the nail, built from compact dead keratinocytes called onychocytes. Unlike the skin's surface cells, these are flatter and do not shed. The plate rests on and is attached to the nail bed, a vascular tissue beneath it that gives healthy nails their pink color. The nail matrix, hidden under the proximal nail fold, is the growth center: its stem cells divide, differentiate, and keratinize to manufacture the nail plate. The visible white half-moon at the base of the nail, the lunula, is the front edge of the matrix. Surrounding tissues, the proximal and lateral nail folds and the cuticle (eponychium), seal and protect the matrix, while the hyponychium seals the skin under the free edge.
Nails grow continuously throughout life as the matrix adds new cells at the base, pushing the plate forward. Fingernails grow faster than toenails, roughly 3 millimeters per month, and full fingernail replacement takes about six months. Beyond protection, nails provide counter-pressure that improves the sensitivity and dexterity of the fingertips and serve as built-in tools.
Because nails grow slowly and reflect events in the matrix, they offer diagnostic clues. Fungal infection (onychomycosis) thickens and discolors nails; psoriasis causes pitting and separation; and systemic disease may produce clubbing, spoon-shaped nails (koilonychia), or transverse Beau's lines. Trauma to the matrix can cause permanent nail deformity, and ingrown toenails are a frequent painful problem. This information is educational and not a substitute for medical advice.