Some interrelations between sebum, sweat and the skin surface.

The recent work of Kligman and Shelley (1) does much to advance our concepts of the physiology of sebaccous secretion. This paper presents several experimental observations that intend to further modify these concepts. The composition of scbum has been thoroughly explored. From an examination of its approximate composition, one would expect sebum to emulsify water as the internal phase of a waterin-oil emulsion, but would not expect it to disperse spontaneously in a large volume of water. Sebum, with some admixed cellular debris, may be collected in relatively large amounts during the warm months by drawing a pharmaceutical spatula across the forehead and flush area, applying light pressure. Under average summer conditions (80° F., relative humidity 50%), the collected schum shows no dispersed water droplets, provided the subject has not been sweating within the previous few minutes. If several drops of freshly collected sebum are touched to a water surface of limited area, e.g., that enclosed by a 150 ml. beaker, the material instantly breaks up and spreads rapidly as a series of globular lenses separated, presumably, by an invisible monolayer. This occurs when the water surface is insufficient to permit all of the sebum to spread entirely as a monolayer. The "spreaders" of this monolayer consist of long chain acids and alcohols, cholesterol, and monoand diestcrs of glycerol. The film may contain dissolved triglycerides, fatty esters and hydrocarbons. This phenomenon may best be observed when the water temperature is 38° C., since the lenses remain liquid and globular. At 30° C. they begin to solidify and become irregular. At neither temperature, observed for periods up to three days, does any of this surface film disperse in water. Neither does this film inhibit the evaporation of water. This may be confirmed at either temperature by comparing the rate of evaporation from the sebum-containing beaker to that Received for publication October 1, 1958. * Clinical Instructor in Dermatology, Southwestern Medical School of The University of Texas, Dallas, Texas.