Sebocytes are highly specialized, sebum-producing epithelial cells that release their content by rupture of the cell membrane and cellular degradation (holocrine secretion). These cells are most commonly found in the skin in association with hair follicles (forming the pilosebaceous unit), where they arise from hair follicle keratinocytes, but there are also sebaceous glands (SGs) not associated with a hair follicle. The latter have special functions as secretion of pheromones or corneal protection. While the full range of sebum functions in human skin remains to be clarified, sebum forms an integral component of the epidermal barrier and the skin immune system. Sebocyte formation is controlled by multiple molecular pathways (e.g. Blimp1, Wnt, C-myc, Hedgehog) and sebum synthesis is strongly regulated by hormones, in particular by androgens. Excessive sebum production is seen in acne vulgaris, one of the most common skin diseases, while deregulated sebocyte differentiation characterizes some rare benign and malignant tumors. © 2009 Elsevier Ltd. All rights reserved.