M. Reinholz

Background Demodex spp. mites are the most complex resident of the human skin microbiome. Although they are considered commensals, they can be pathophysiologically relevant in inflammatory skin diseases like rosacea. Until now, there is no culture system available for these mites except for using live vertebrate hosts. Objectives Our aim was to establish an ex vivo culture of human Demodex mites and to characterize the sebogenesis‐dependent mite density. Methods Demodex mites were cultivated in pilosebaceous units of human skin explants, called human organotypic skin explant culture (hOSEC). Furthermore, different sebogenesis‐modifying additives were evaluated. Mites and mite survival were evaluated using light and fluorescence microscopy. Results After 90 days of incubation, living Demodex mites – including eggs, larvae and nymphs – were detected in the dissected skin samples. Incubation for 30 days with anabolic steroids (testosterone and trenbolone) as well as retinol and retinoic acid (isotretinoin) yielded a reduced mite density. Conclusions With this technique, mites can be cultivated ex vivo for the first time, thereby establishing new ways to investigate Demodex spp. The sebostatic effect of isotretinoin might explain the mechanism of action in the off‐label treatment of rosacea. We anticipate our findings to be the basis of an accelerated research on our most complex commensal, its life, biology and physiology.