**Figure 1.** **Influence of selenium on cell viability and proliferation.** Effects on cell viability after application of a range of NaSe concentrations during 72 h for (**A**) fibroblasts and (**B**) keratinocytes. Viability is calculated as the “(mean of treated cells–mean of blank) / (mean of untreated cells–mean of blank)” ±SD (n=3 donors and n=12 measurements per conditions). The stars illustrate statistical differences between 100% and mean of experimental points. Effects of 3 Selenium concentrations on clonogenic potential of keratinocytes from 3 donors after 12 days of supplementation. (**C**) Representative aspect of the colonies at different concentrations versus the control, (n=3; scale bar=1cm) and (**D**) CFE ratio are calculated to avoid inter-individual heterogeneity of CFE. *p<0.05; **p<0.01; ***p<0.001.