Human skin surface lipid is derived from endogenous and exogenous sources. Major endogenous sources are the sebaceous glands  and the epidermis; very minor endogenous sources are bacteria and (possibly) eccrine and apocrine secretions. Exogenous sources are cosmetics, ointments used in topical therapy and soaps.

 

  As the most important endogenous sources of surface lipid in man  are  the epidermis and  the  sebaceous glands, the relative contribution of each to the ultimate surface lipid composition can  vary. Thus, areas rich in sebaceous glands, such as the forehead, have a surface lipid composition more approaching that of pure sebum than have areas  of  skin  less  well  endowed  with sebaceous glands.