180 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS tion capacity of the lipids of the human skin surface and proved the fallacy of the concept that the waxy coat interferes with the wetting of the surface (26). And ever since that date investigators have been supplying more and more convincing evidence that sweat and surface lipids not only have a strong mutual emulsifying capacity, but are actually to a large degree inter- depend•nt and coupled in the carrying out of their joint functions. Of the various types of evidence supporting the above concept the follow- ing represent only a few selected examples: •uantitative Studies of Sweat and of Skin Surface • ipids Quantitative Parallelism in the Skin Areas Studied. In systematic quantitative studies on large series of human volunteers, Herrmann and co-workers in my department have demonstrated a striking parallelism in the amounts of sweat and the amounts of ether-soluble material on the human skin surface (15, 21, 22, 23, 4, 20). In all areas studied save two (the axillae and the mid-forehead), when there was a large amount of sweat there was also a large amount of lipids and vice versa, when the sweat quantities were small the lipid quantities were likewise. This quan- titative parallelism is most instructively shown in those cases in which sym- metrically situated skin sites did not sweat equally in the usual manner, i.e., in which the delivery of sweat to a selected area on one side of the body was regularly and consistently much more or much less than the sweat delivery to a corresponding contra-laterally situated area.* in all such cases the quantities of ether-soluble substances closely paralleled the quan- tities of sweat, i.e., were regularly greater on the site with greater sweat delivery and less on the symmetrically situated site with lesser sweat delivery (15, 21, 4). Sex-Linked Parallelism. A further demonstration of quantitative paral- lelism is brought to light by the sex-linked quantitative differences in the delivery of both types of substances. Rothman and Kahn (27), Shelley and Gibson (28), as well as our own systematic quantitative studies (15, 21, 4) demonstrated that on all the selected skin areas studied, males regularly deliver more sweat than females upon thermal or other forms of cholinergic stimulation. And several investigators found that these same quantitative sex-linked differences obtain also in regard to ether-soluble substances of the skin's surface--the lipid quantities being greater in males (29, 30). * We encountered a symmetrical sweat delivery in about 20 per cent of our healthy volun- teers (15). This rather high incidence may be of special interest for this audience. For any assays of the effect of externally applied agents on the degree of sweating, e.g., of the effect of antiperspirants, it is evidently imperative to carry out preliminary "blank" examinations in each test subject, in order to ascertain whether or not there is symmetrically equal outpour- ing unless this is done one will not be able properly to evaluate findings obtained on sym- metrically situated test and control areas.

CLINICAL DISTURBANCES IN SWEATING 181 Parallelism in Response to Environmental Temperature and Humidity on the Part of Both Sweat and Surface Lipids. In addition to the in- controvertible clinical dermatologic evidence pointing in this direction, there is general agreement among many competent laboratory investigators that the amount of ether-soluble material on the skin surface increases at ei evated environmental temperatures and decreases at low environmental temperatures (31, 32, 33, 34, 21, 23, 35). Certain highly competent ex- perts in this field, notably Butcher and Parnell (32), as well as Duenner (34)* believe that this increase is due to the decreased viscosity and in- creased flow of the lipids themselves (sebum) at the higher environmental temperatures and do not believe that sweat is in any way responsible for this effect. We are of course in agreement with Butcher and co-workers (32, 33) and with Duenner (34) in recognizing the part played by the low- ered viscosity of the sebum and other lipids at higher temperatures and the effect which this has in accelerating the flow and replacement of the lipid surface film. However, we believe we have good reasons for regarding the decreased viscosity of the total surface film as only partly due to the effects of temperature on the lipids per se and in greater degree due to the effects of increased sweating produced by the higher temperatures. Many old-established dermatologic observations, as well as newer clinical findings all support the concept of the role of sweat in promoting the delivery and spread of the lipid film. Thus, for example, it is a well-known clinical fact that it is in the en- vironments with consistently high relative humidities as well as high tem- peratures that the skin surface tends to be at its "greasiest" and "oiliest," an observation pointing to the role of sweat, since at high environmental humidity the sweat will evaporate more slowly and remain longer and in greater quantity on the skin surface. This effect has not only long been * Butcher and Parnell (32) as well as Duenner (34) submit experimental data in support of their opinion that sweat is not in any way responsible for this thermogenic effect upon the lipid film. However, it seems to us that their results do not necessarily prove their point, but are susceptible to alternate interpretations. Thus in the experiments of Butcher and Parnell, CaCh was kept in the dome of a metal cup "high" above the test area, with the ob- ject of removing the H•.O evaporating from the skin. The skin lipid film, however, presum- ably takes up the water (sweat) immediately at the skin surface and thus may "get there fustest" and "win" in the competition with the CaC12 for the uptake of most of the water. Moreover, the tight enclosure of the tested skin area by the wall of a metal cup is certain to increase the lipid level on that area as compared with the level on an uncovered control area, even without any increase of skin temperature or humidity (sweat). For the enclosure by such a cup not only affords protection against chance wipings off of the surface film, but more important still, allows accumulation of a considerably greater amount of this film by inhibiting its spread. The higher level obtained in such an enclosed and protected area is precisely what we have called the "total" or "protected" level in contrast to the "casual" or "unpro~ tected" level (see p. 183). The strong tendency of the lipids to spread over the skin surface was first observed by Butcher and Parnell (32) and its rate exactly measured by Jones and collaborators (24). The significance of this effect for the quantitative determinations of the lipid level on the skin is made evident by the studies of Kvorning (36) as well as by our own investigations (21,23,20).