The study of endogenous porphyrins in human skin and their potential for photodynamic therapy by laser induced fluorescence spectroscopy

Human skin shows a strong autofluorescence in the red spectral region when excited by the 407 nm radiation of a krypton ion laser. The spectrum consists of three main peaks around 600, 620 and 640 nm, which are typical for metalloporphyrins such as Zn-protoporphyrin, coproporphyrin and free protoporphyrin IX, and perhaps represent a mixture of these compounds. The fluorescence is located in sebaceous follicles which contain large amounts of the porphyrin-producing skin bacterium Propionibacterium acnes. Irradiation, especially with violet light, reduces both the integral fluorescence intensity and the number of living bacteria. The process of photobleaching is oxygen-dependent. In addition, irradiation results in the formation of fluorescent photoproducts with spectral bands similar to photo-protoporphyrin. It seems to be possible to use the endogenous porphyrins for a photodynamic therapy of acne vulgaris and to monitor the therapeutic effect by the simultaneous measurement of spectral changes.