erythrasma is a superficial cutaneous infection caused by corynebacterium minutissimum and is characterized by fluorescence under wood s light uv because of the presence of porphyrins these molecules are photosensitizing and we propose to assess efficacy of red light that activates porphyrins photodynamic reaction in treatment of this pathology assessment of effects of photodynamic action of red light for treatment of erythrasma without exogenous photosensitizing molecules thirteen patients with erythrasma were treated by one illumination 80 j cm2 by red light broad band peak at 635 nm without exogenous photosensitizing molecules disappearance or reduction of extent of lesions were observed 2 weeks later if lesions were still present a second irradiation was conducted with the same method preliminary results are presented as a result of red light irradiation we noticed a complete recovery for three patients and in most other cases reduction of extent of lesions mean 29 after one session the treatment was well tolerated we report first cases of photodynamic treatment of erythrasma there are other reports of clinical applications of antimicrobial action of photodynamic therapy in dermatology acne vulgaris leishmaniasis warts etc but there are few applications without addition of exogenous photosensitizing agent the originality and interest of our study is to use spontaneous presence of porphyrins in the lesions this technique seems to be an interesting alternative inexpensive and easy for the treatment of this localized infection but an optimal method is still to be determined to improve efficacy.