Nanoceria reduced UVB-induced cytotoxicity in HaCaT cells. (A) Cell number and (B) apoptosis of HaCaT cells at 24 h following UVB 0.18 J/cm2 exposure. The viable cell ratio was obtained as a normalized value over day 0. Statistical significance was calculated via Student’s t-test. * p < 0.05, ** p < 0.01 and *** p < 0.001, with respect to UVB-irradiated cells. (C) Time course of viable (trypan blue-excluding) cell number (expressed as fold over day 0) upon 15 s exposure to UVB ± nanoceria (CNPs). (D) Kinetics of the fraction of apoptotic cells upon 0.18 J/cm2 exposure to UVB ± nanoceria (CNPs). Statistical significance was calculated via Student’s t-test. * p < 0.05, ** p < 0.01, *** p < 0.001, with respect to UVB-irradiated cells.