Borelli, C.; Merk, K.; Schaller, M.; Jacob, K.; Vogeser, M.; Weindl, G.; Berger, U.; Plewig, G. In Vivo Porphyrin Production by P. Acnes in Untreated Acne Patients and Its Modulation by Acne Treatment. Acta Derm Venereol 2006, 86, 316-319.