VOLATILE COMPOUNDS FROM HAIR AND SCALP 9 10 20 30 min. I I I Figure 5. Chromatogram of the volatile compounds from human hair of a 30-year-old male. Sample: 130 mg of hair. Dynamic headspace procedure with FFAP column. The darkened peak marked "a" corresponds to a contaminant introduced in the mixture by the sampling apparatus. Flame ionization detection. composition of the volatile compounds sampled can be mostly disregarded. Several experiments showed that there were no detectable discrepancies between the volatiles sampled at 25-30øC and those sampled at 50øC. The latter was preferred since the reduced time of purge resulted in a higher sample throughput. Thus, it is certain that the volatile compounds detected in this study were originally present on the hair and the scalp at the time the sample was collected. To our knowl- edge, these species have never been cited as endogeneous compounds synthetized by either the sebaceous glands or by the keratinizing epidermis. Due to the chemical nature of the compounds identified, it seems very unlikely that they are contaminants depos- ited on the hair and the scalp from the environment. The only plausible hypothesis we can give to the origin of these volatiles is through in situ transformations of the original skin surface lipids. This hypothesis is aided by the presence of odd and even carbon-atom-number chains. This rather uncommon feature is very characteristic of skin surface lipids. It is well known that lipids exposed to the ambiant environment are subject to auto-ox- idation, thermo-oxidation, photo-oxidation . . . etc., yielding various hydroperoxides. The latter are then involved in further transformations including the cleavage of ali- phatic chains. These phenomena have been studied extensively, and almost all of the compounds listed in Table I have been associated with the oxidation of lipid material by one author or another (18-26). The studies cited above were mainly concerned with

10 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 5 10 I • 15 20 min. Figure 6. Chromatogram of the volatile compounds originating from squalene after oxidation in air at 120øC for two hours. Detection by mass spectrometry (total ion current). The major peaks in the chromato- gram correspond to oxygen-containing compounds with chain lengths of C 2 to C 5. They elute before the start of the chromatogram shown in Figure 3. fatty acids or triglycerides, while in human skin surface lipids another important autox- idable compound, squalene, is present (27). Indeed, we could observe that, after oxida- tion in vitro, squalene actually released a number of volatile breakdown products as illustrated in Figure 6. On the other hand, the hair and the scalp harbor a microbial flora which exhibits some capability of biotransformation of skin surface lipids the hydrolysis of triglycerides into free fatty acids is a classical example of such a transformation. Thus, it cannot be excluded that some of the volatile compounds we identified originated through a bio- transformation of the skin surface lipids by the resident flora. Although the production of volatile species by microorganisms is well documented in the literature, few details have been published concerning the species which are usually or even occasionally encountered on human hair and scalp. Thus, 2-nonanone and 2-undecanone have been cited as characteristic of Pseudomonas aeruginosa (28,29) which is not a permanent resident on human normal skin but rather transient in nature (30). Propionibacterium acnes, a resident on normal skin, is known to be capable of producing short-chain carboxylic acids (31,32), a behavior they share with a number of other strains. Members of the genus Pityrosporum, including the skin residents P. ovale and P. orbiculare, were shown to produce characteristic •/-lactones when grown on lipid-containing media (33). By determining the chirality of the •/-lactones