Figure 3. MODEL SYSTEM FOR DANDRUFF INVESTIGATION 195 30- G5 0 ß ß Sloughing Grade Relative concentration of C•s monoenoic acid in ether:methanol extracts ooe sloughing sites irritated with increasing amounts of P. ovale cells o & 7o• ,•o •$o •o •o ml oleic acid/cm z Figure 4. Effect of increasing conccntrations ooe oleic acid on relative sloughing grades marked increase in the relative content of C•.s monoenoic acid in extracts [rom those sites (P. ovale and diphtheroid) which produced extensive sloughing. Further data (Fig. 3) indicate that in the case of P. ovale- irritated sites, the degree o[ desquamation correlated with the concentra- tion o[ C•s monoenoic acid in the extracts of the sites. Addition monoenoic acid (oleic) to artificial sebum alone produced a definite irri- tation and sloughing (Fig. 4) which appeared grossly similar to that in- duced by microorganisms in artificial sebum. Other C•s monoenoic acids such as vaccenic, elaidic, and petroselinic when similarly tested pro- .duced comparable sloughing at approximately the same concentration as oleic. Concentrated extracellular products obtained by dialysis o[ centri- fuged, spent culture medium in a vacuum chamber similarly produced increases (Table V) in relative concentration o[ C•s monoenoic acids and, in the case of the diphtheroid, an increase in C•s dienoic acid content.

196 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table V Effect of Concentrated Extracellular Products of Scalp Microorganisms on Sloughing and Fatty Acid Content of Artificial Sebum Quantity of Extracellular Product Per Gram of Artificial Sebum P. Ovale Diphtheroid 0.1 ml 1.0 ml 0.1 ml 1.0 ml Av sloughing grade 1.7 1.7 1.3 1.7 % Change in free fatty acids -- 0.9 q-. 4 q- 1.1 q- 3.9 % Relative increase in Cts (1=) 2.86 8.66 2.52 4.77 % Relative increase in Ct8 (2•) None None 0.45 4.39 Tributyrinase activity, •g/min/ml . . . 0.9 ... 2.5 DISCUSSION The observed guinea pig sloughing reaction initially develops as patent erythema appearing within 3-4 hours after application of the lipid-microorganism matrix. The erythematous reaction is followed by desquamation of the stratum comeurn not unlike the primary irritation produced by sodium lauryl sulfate. Guinea pigs appear to be particu- larly suitable as test animals because they react to the l ipid system with a greater degree of predictability than other com•non laboratory animals: they are docile and restraints are unnecessary. In cases of extremely severe irritation, open lesions were occasionally observed which were the result of scratching the irritated area by the animal. The lesions normally healed uneventfully and did not impair the usefulness of the particular animal in subsequent testing. Normally, a recovery period of 6 to 7 weeks following initial test applications was allowed before the animal was again subjected to testing. Tht most severe sloughing reactions appeared when P. ovale was admixed to the artificial sebum. Although this organism did not ex- tensively hydrolyze tributyrin in vitro, it did appear to produce a greater relative increase in C•s monoenoic acid than the more actively lipolytic but less irritating diphtheroid. The demonstrated ability of P. ovale to produce guinea pig sloughing would appear to agree with the recent work of Gosse and Vanderwyk (13) who found that application of the anti- biotics nystatin and neomycin to the scalps of 11 human subjects pro- duced a 63.4% average reduction in dandruff. The subsequent de- liberate recolonization of these subjects with a nystatin-resistant P. ovale