5-FU (Merck KGaA), which was used for the data shown in the supplementary figures, was dissolved in physiological solution at a final stock concentration of 3.84 mM. The appropriate concentration of 5-FU in distilled water was assessed for each cell line by estimating the IC50 after 72 h in 75 μM for A431 cells and 100 μM for HaCaT cells. Each group, following light exposure, was divided into 2 subgroups, treated or not treated with the IC50 of 5-FU for 72 h at 37°C and 5% of CO2; cell viability assay was then performed.