Human hair follicles (HFs) were isolated and irradiated (8 Gy) or treated with 3% hydrogen peroxide. A. Viability was tested at days 0, 2, 5 and 7 post treatment using immunofluorescent staining for Ki-67 (a proliferation marker; red) and TUNNEL assay (apoptosis; green) in the ORS (Scale bar; 50μm). B. Ki-67-and TUNNEL-positive cells were quantified and normalized to DAPI-positive ORS cell counts. Data are mean ± standard error of mean (SEM). n = 2 human donors; 48-50 hair follicles from each donor were analyzed; n.s., not significant; p values were determined by two-way ANOVA. C. Immunofluorescent staining of hair follicles for the DNA damage marker (γ-H2AX; purple), for hair follicle at the bulge (CD200; red), and for nuclei (DAPI). Scale bar, 50μm. The percentage of γ-H2AX-positive cells were calculated out of the total DAPI-positive cells at the bulge area (CD200-positive area). Data are mean ± SEM. 48-50 hair follicles were analyzed from each of 2 independent donors. p values were calculated by the two-tailed Student’s t-test; p < 0.05 is considered statistically significant.