Unusual pigmentation on the skin over trunk bones and extremities

6 young people (19-31 years old) exhibited unusual light or dark brown, ill-circumscribed or reticular pigmentation distributed over protrudent bones. 5 of them have been using nylon towels and scrub brushes for over 3-10 years. Biopsy specimens showed that the amount of melanin granules in the basal layer was increased and melanophages were scattered in the upper dermis. Inflammatory infiltrates were minimal.