The present invention relates to a process for evaluating in vitro at least one active agent capable of preserving the functionality of epithelial stem cells, in particular of maintaining or stimulating the growth and/or the density and/or the renewal of a keratin material, consisting in determining the ability of the active agent(s) to mimic a hypoxic state in the keratin material, the active agent(s) being capable of increasing the expression of at least carbonic anhydrase IX as biological marker of hypoxia, in the keratin material treated with the active agent(s) compared with the keratin material not treated with the active agent(s). It also relates to the use of such a process.