Downward growth of epidermal cells results in the formation of the primordial hair follicles. The sebaceous gland arises from a bulge in the epithelium of the hair follicle above the level of the insertion of the arrector pili muscle. The rapid development of this structure in the fetus is driven by maternal androgenic hormones. The gland is fully functional well before birth. This hypothesis is supported by the presence of the vernix caseosa, a cheesy substance composed of sebum and adherent cornified cells, on the skin of newborns and by the occurrence of neonatal acne, a fine papulopustular eruption on the faces of newborns.
Androgenic hormones play the dominant role in regulating sebaceous gland activity.
The composition of sebum differs from that of epidermal surface lipids in that some of the triglycerides in sebum have been hydrolyzed to free fatty acids. However, topical application of potent inhibitors of bacterial lipases, which rapidly inhibit the formation of free fatty acids, has since been shown to alter neither the sebum secretion rate nor the number of lesions. It is now thought that free fatty acids play a minimal role in the pathogenesis of acne.