The development of a filter to enhance the efficacy and safety of excimer light (308 nm) therapy

Background: Excimer light (308 nm) therapy is a new ultraviolet (UV) B phototherapy for which the efficacy and resulting DNA damage are not well established. Purpose: To develop an effective and safe phototherapy using the excimer lamp, we studied the effects of different light cut-off filters, A and B. Methods: Efficacy was evaluated by measuring apoptosis using fluorescence-activated cell sorting analysis. DNA damage was evaluated by measuring cyclobutane pyrimidine dimers (CPDs). Light sources, including normal wave and short wave (SW) excimer light, broad-band (BB) UVB, and narrow-band (NB) UVB, were examined using the filters. A human skin equivalent model was also examined. Results: The ratio of positive apoptosis to CPD formation normalized to the mean induced by NB-UVB was 5.7 using the excimer lamp without a filter, 6.3 using the excimer lamp with the A filter, 6.4 using the SW excimer lamp without a filter, and 4.2 using the BB-UVB. The A filter reduced CPD formation induced by the normal wave and SW excimer lamp. In the human skin equivalent model, the use of filters significantly decreased the amount of CPD-positive cells. Conclusions: These findings suggest that using the A filter with the excimer lamp increases the efficacy and safety of excimer light therapy.