Living skin cells within the fingers and toes produce nails, which are primarily composed of keratin, a hardened protein also found in skin and hair. The nail consists of several different parts, including the nail plate, nail bed, matrix (hidden area under the cuticle), lunula (part of the matrix at the base of nail), cuticle (tissue that overlaps the nail) and the nail folds (skin framing the nail). In addition to having a cosmetic appeal, nails provide several important functions. Fingernails and toenails protect the sensitive skin underneath. Fingernails aid in the gripping of objects, and they also scratch.
The average growth rate for nails is 0.1mm each day; individual rates depend on age, time of year, activity level and heredity. On average, nails grow about one tenth of an inch (2.5mm) each month. At that rate, it can take from three to six months to completely replace a nail. Fingernails grow faster than toenails. Nails also grow more rapidly in the summer than in the winter. Nails on a person's dominant hand (right vs. left) grow faster. Men's nails typically grow more quickly than women's nails. Disease, hormone imbalance (caused by pregnancy or other conditions), and the aging process may affect nail growth. For example, yellow or green discoloration in nails may result from a respiratory condition such as chronic bronchitis or from swelling of hands (lymphedema). Indentations that run across nails, called Beau's lines, appear when growth at the area under cuticle is interrupted. This might occur because of an injury or severe illness, such as a heart attack.
Manicures and pedicures are most often recommended for primarily cosmetic purposes. Currently, available research regarding the safety and efficacy of nail treatments is lacking, most likely because such treatments are not considered necessary to keep nails healthy, and are not thought to treat any nail condition. Most nail treatments deal with only the most external portion of the nail and surrounding skin.
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