History: Reactive perforating collagenosis is an inherited condition characterized by pinhead-sized, skin-colored papules that develop a central area of umbilication in which keratinous material is lodged. The discrete papules may be numerous and involve sites of frequent trauma such as the backs of the hands, forearms, elbows, and knees. The lesion reaches a maximum size of about 6 mm in 4 weeks and then regresses spontaneously in 6 to 8 weeks. Koebnerization is often observed.