Effects of the chorion-derived stem cell conditioned medium (CDSC-CNM) on the cell cycle progression of photo-aged HaCaT cells. After being treated with CDSC-CNM, HaCaT cells were stained with PI and analyzed using flow cytometry. (A) a: Non-irradiated HaCaT cells in a control medium (CM); b: UVB-irradiated HaCaT cells in CM; c-f: UVB-irradiated HaCaT cells treated with 25%, 50%, 75% and 100% CDSC-CNM, respectively. (B) The percentage of HaCaT cells in the G0/G1, S and G2/M phases following treatment with different concentrations of CDSC-CNM. Data are presented as the average ± SD from three independent experiments.