Melatonin, NAS, 6-OHM, AFMK, and 5-MT increase viability of HEKn keratinocytes exposed to UVB. Data are calculated by subtracting viability from non-irradiated cells which means we considered the anti-proliferative effect of melatonin and its derivatives on this cell. Data were analyzed using student t-test, * p<0.05, ** p<0.01, and *** p<0.001.