The nail plate is a hard keratinized structure derived from keratinocytes within the nail matrix, which begins proximal to the nail plate and extends to the lunula, the white half-moon shaped portion often seen through the nail plate. The proximal and distal nail matrices generate the dorsal and ventral nail plate, respectively. The nail bed beneath the nail plate extends from the lunula to the hyponychium, and the hyponychium lies under the free edge of the nail plate. The proximal and lateral nail folds comprise the paronychium.
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The primary function of the nail is protection. Nail concerns are common, but the exact prevalence of nail disease is unknown. Nail disease occurs with certain skin diseases (psoriasis, eczema), often follows external trauma, may be an adverse effect of medication, and may occur with certain illnesses. The most common cause of nail disease is infection, usually fungal (onychomycosis) and less often bacterial. In many respects, the nails may indicate or reflect medical illness.
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