Photodynamic action of the red laser on Propionibacterium acnes

Background: photodynamic therapy is a therapeutic modality that has consolidated its activity in the photooxida-tion of organic matter,which arises from the activity of reactive oxygen species. objective: to evaluate the effect of red laser 660nm with the photosensitizer methylene blue on propionibacterium acnes in vitro. method: the experimental design was distributed into four groups (1 - control group without the application of light and without photosensitizer,2 - application of light,3 - methylene blue without light,and 4 - methylene blue with light). tests were subjected to red laser irradiation 660nm by four cycles of 5 minutes at 3-minute intervals. results: it was evidenced the prominence of the fourth cycle (20 minutes) groups 2,3 and 4. study limitations: despite the favorable results,the laser irradiation time photosensitizer associated with methylene blue were not sufficient to to completely inhibit the proliferation of bacteria. conclusion: further studies in vitro are recommended to enable the clinical application of this photosensitizer in photodynamic therapy. © 2017 by anais brasileiros de dermatologia.