The nail is a specialized keratinous skin appendage that grows approximately 2 to 3 mm per month, with complete replacement achieved in 6 to 9 months. Although this structure can be easily overlooked, nail disorders comprise approximately 10% of all dermatologic conditions. This contribution first provides an overview on the basic anatomy of the nail that will delineate between the nail unit (eg, hyponychium, nail bed, proximal nail fold, and matrix) and anatomic components not part of the nail unit (eg, lateral nail folds, nail plate, and eponychium). The function of each nail structure will also be presented. The chemical profile of the normal nail plate is reviewed with a discussion of its keratin content (hair type keratin vs epithelial type keratin), sulfur content, and mineral composition, including magnesium, calcium, iron, zinc, sodium, and copper. The remainder will focus on nail manifestations seen in states of malnutrition. Virtually every nutritional deficiency can affect the growth of the nail in some manner. Finally, the discussion will include anecdotal use of nutritional and dietary supplements in the setting of brittle nail syndrome as well as a brief overview of biotin and its promising utility in the treatment of nail disorders.
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