Light protection of the skin after photodynamic therapy reduces inflammation: an unblinded randomized controlled study

Background Photodynamic therapy (PDT) is followed by significant inflammation. Protoporphyrin (Pp)IX is still formed in the skin after PDT and patients are sensitive to daylight 24-48 h after treatment. Exposure to daylight after PDT may therefore increase inflammation. Objectives To investigate whether protection with inorganic sunscreen, foundation or light-blocking plaster after PDT can reduce inflammation caused by daylight-activated PpIX. Methods On the right arm of 15 subjects with sun-damaged skin, four identical squares (3 x 3 cm) were given conventional PDT treatment. Immediately after red-light illumination the squares were either left unprotected or protected by inorganic sunscreen [sun protection factor (SPF) 50], foundation (SPF50) or light-blocking plaster. The skin was then illuminated with artificial daylight for 2 h and afterwards covered for 24 h. Fluorescence and erythema (inflammation) were measured with a fluorescence camera and a reflectance meter. Results PpIX was significantly reduced after artificial daylight illumination (P < 0.0004), except on the square protected with light-blocking silver plaster, where it had increased (P = 0.09). The increased erythema 24 h after treatment was reduced by 19% with the sunscreen (P = 0.29), by 27% with the foundation (P = 0.10) and by 44% with the silver plaster (P = 0.002). Conclusions Artificial daylight exposure after conventional PDT increases skin erythema. Light-blocking plaster gives more effective protection against post-PDT daylight exposure than inorganic sunscreen and foundation. In practice such full protection can be achieved by use of sun-blocking clothes or daylight avoidance for 24 h.