CONSIDERING THE wide riety of surface-active agents com- merically available, it is interesting to note that the cosmetic industry utilizes so relatively few of these ma- terials in shampoo formulation. These favored products are almost, without exception, fatty acid soaps or fatty derivatives of the anionic type they enjoy a sort of historical priority and this accounts, at least in part• for their preferred position. However, there does not seem to be any reason why many of the neg- lected materials may not find some useful place in shampoo manufac- ture if properly formulated or purl fled. One barrier to the more ef- ficient utilization of available ma- terials has been the development of some rather interesting misconcep- tions regarding surface-active agents and the effects which they produce. A blanket objection often raised against synthetics is that they are excessively drying or defatting. The literature, however, is sadly lacking m evidence that the synthetics dif- fer significantly from soap as to ef- ficiency in removing fatty materials •--•Presented at the May 20, 1949, Meeting, New York City. SHAMPOO FORMULATION* By H. W. ZussMAr /1/rose Chemical Company, Providence, R. ]. from protein fibers. Evidence of actual extraction from the skin of lipoids by aqueous solutions of de- tergents is also unavailable. There appears to be a division of opinion among dermatologists on such mat- ters as permeability,.•of the skin to water or its ability 'to absorb fat dispersed in surface-active solu- tions. While there is no reason to doubt that surface-active agents do remove surface oils from the hair and skin, it is well to bear in mind that these surface oils are excretions and, secondly, that the sebaceous glands are continuously replacing these surface oils. It might also be pointed out that at least some lipoid material on epithelial surfaces is in a "bound" state and is not readily re- moved under any but the most stringent conditions. Stoves (1) reported that the medulla of kolin- sky fur fiber contained a lipold-pro- tein which will not yield its fatty component (sterol) on extraction with chloroform or with synthetic detergent but is hydrolyzed only by boiling with 7.5 per cent alcoholic sodium hydroxide for two hours. In view of the absence of conclu- sive data on the removal of subsur- 355

356 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS face lipoids, it may be desirable to describe the so-called defatting re- action of synthetics in sensory terms. If the hands are washed with a rela- tively concentrated solution of puri- fied neutral Cn alkyl aryl sulfonate, a copious lather with good lubricat- ing properties may be worked up. As the hands are rinsed and as the suds disappear, one becomes aware of the abrupt development of a high coefficient of friction making it very difficult to pass one palm over the other a peculiar crackle is also pro- duced. On towelling the hands a tackiness may be noted but this dis- appears on complete drying. If the hands are rewetted, the high coef- ficient of friction of the skin is again evident. This sensation is generally believed typical of ultra- clean skin. Now if this is true de- fatting there are several facts which are rather-difFicult to explain: (1) Short chain alkyl naphthalene sulfo- nates which are notoriously poor detergents and fat emulsifiers pro- duce the same effects as the high molecular weight alkyl aryl sulfo- nates while oleic acid soaps, which are generally conceded to be excel- lent fat emulsifiers, do not "di'y" the skin. (2) Real defatting of the skin with organic solvents does not produce effects similar to those ob- tained even with the most powerful neutral synthetic detergents. (3) The skin of the palms, where the "drying" effect of the synthetics is most pronounced, is notably lack- ing in sebaceous- or oil-secreting glands. These circumstances sug- gest that actual defatting of the skin may not be a satisfactory ex- planation for the phenomenon just described. , The effects produced on the skin by synthetics may be better de- scribed as "scroop" to borrow a term from the textile industry--this is a finish imparted to silk by treat- ing with dilute organic acid. It is characterized also by a h. igh coefFi- cient of friction and a crackle or rustling sound when the silk is rubbed on itself. Going back to the demonstration of "scroop" produced on the skin by the alkyl aryl sulfonates, it will be remembered that after rinsing and drying the skin was considered clean. If the hands are now rinsed with dilute sodium carbonate (less than 0.25%), it is possible to work up a suds again at the same time the normal feel of the skin is re- stored and now remains unchanged even after copious rinsing with pure water. The skin, of course, is pre- sumably no cleaner now than be- fore. This suggests that the sensa- tion of an ultra-clean skin surface was produced actually by an ad- sorbed film of surface-active agent. In[identally, if the hands are washed with alkyl aryl sulfonate at neutral pH in the presence of sodium sulfate, or at pH 3 to • in the pres- ence of organic acid, the "scroop" effect produced is considerably en- hanced in either case, rinsing with dilute alkali restores the normal feel. C-12 alcohol sulfates and alkyl sulfonates of low salt content at neutral pH produce less "scroop" than do the alkyl aryl sulfonates..