Verruca vulgaris. The common wart is a benign growth caused by localized infection with one of the many types of human papillomavirus. These small DNA viruses are part of the papovavirus group. Warts are especially common among children and adolescents and may occur on any mucocutaneous surface. The hands are a particularly frequent location. The typical wart is a roughsurfaced nodule that may be either lighter or darker than the surrounding skin.
Trachyonychia (twenty nail dystrophy of childhood). Any skin disease that affects the nail matrix may result in an abnormal nail plate. There are children, though, who only manifest dystrophy of the nail without any other cutaneous lesions, a condition that has been termed twenty nail dystrophy of childhood. The nails have a rough, sandpaper-like quality as well as longitudinal ridging and occasional splitting at the distal nail edge. Similar nail changes can be seen in lichen planus and alopecia areata. In many patients the condition spontaneously regresses.