Despite lavish care, human nails like human hair are not essential. These appendages, which were presumably more appropriate to our ancestors, are subject to a bewildering variety of abnormalities and diseases which we as physicians are asked to treat and correct. This and succeeding communications are an attempt to present a simplified orderly approach to the more common nail disorders.
New nail is formed under the posterior nail fold by the nail matrix and pushes the already formed nail distally over the nail bed at a rate of approximately 0.13 mm per day. This process of nail formation can best be appreciated by observing the appearance and movement of the transverse ridges or "Beau's lines" (Fig 1) which form in all nails during periods of severe systemic illness. These ridges emerge from under the posterior nail fold, move distally, and are followed by normal nail as the internal problem is
Halprin KM. Afflictions of a Vestigial Appendage: I. Congenital Defects of the Human Nail and Systemic Influences. JAMA. 1967;202(7):645. doi:10.1001/jama.1967.03130200131023
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