Comparative chemistry of sebum.

Sebum is the excretory product of the sebaceous glands. These glands are found in the s kin of all mammals excep~ whales and porpoises (Montagna. 1963). The bulk of sebu m is a mixture of relative ly nonpolar lipids, most of which are synthesized d e novo by the gland. The lipid is excreted by a "holocrine mechanis m , whereby the lipid-laden cells dis integrate and pour their content s through the sebaceous duct onto the s kin s urface. One apparent function of sebum is to provide the s kin surface and hair with a hydrophobic coating. The preen gland of birds has a s imilar func tion, but it is not a sebaceous gland . The preputial glands of rodents are s pecialized sebaceous glands, used primarily for the re lease of pheromones. The c hemistry of sebum is interesting, because many compounds not found elsewhere i.n the body have been identified in sebum . As firs t was clearly shown by Wheatley (1956). the compos ition of sebum is remarkably species s pec ific. The application of modern chromatographic methods to studies of sebum has greatly expanded our knowledge of its chemis try during the last two decades. There have been some comparative s tudies (Wheatley and J a mes, 1957; Nicolaides et al.. 1968. l970; Nikkari, 1969), but in m ost studies each investigator has worked on one s pecies only. The present review s ummarizes the results of different authors in a form that allows easier compa rison among various species.