Treatment of pilonidal sinus and acne inversa Der Hautarzt; Zeitschrift fur Dermatologie, Venerologie, und verwandte Gebiete (in German) March 2004 Breuninger H. Universitats-Hautklinik, Tuebingen. A pilonidal sinus is a invagination of the skin over the sacrum containing a tuft of hair which enlarges by repeated friction causing the hairs to penetrate the skin. It may become symptomatic if an infection occurs. There are similarities with acne inversa, which is present in about 23% of cases. Acne inversa is an inflammation of the sebaceous glands and terminal hair follicles, chiefly in the intertriginous areas. The first manifestation can occur at any time from puberty to advanced age. 90% of patients are smokers. Initially giant comedones and indolent subcutaneous nodules are found; they progress to form draining sinus tracts. Conservative treatment, incision and/or surgical removal of the abscesses and fistulas is futile. The method of choice is the early complete surgical excision of the involved skin extending into normal tissue both laterally and at the base. In most cases healing of the defects by secondary intention is uneventful.