j. Soc. Cosmet. Chem., 33, 317-343 (November 1982) Hair lipids and their contribution to the perception of hair oiliness: Parts I and II j. KOCH, K. /IlTZETM•LLER, G. BITTORF, andJ. [I/lIBEL, Unilever Forschungsgesellschafi mbH, Behringstrasse 154, 2000-Hamburg 50, [Vest Germany. Received October 6, 1981. PART I: SURFACE AND INTERNAL LIPIDS IN HAIR Synopsis Standard conditions for the extraction of surface lipids from hair have been developed. The hair samples are conditioned for 2 h in a water-saturated atmosphere and then extracted for 20 min with water-saturated ether under reflux. Under these conditions all components of the external lipids are extracted indiscriminately with respect to their chemical nature. Evidence is provided for the existence of "internal" sebum in human hair which is not extractable under conditions aimed at simulating the strongest shampooing conditions imaginable in practice. After extraction of the external lipids with boiling H20-saturated ether and removal of Ca-bridge bound fatty acids of the hair surface with ethereal hydrochloric acid, the internal lipids were isolated by enzymatic hydrolysis of the hair keratin and subsequent extraction of the residual membranes. High performance liquid chromatographic analysis reveals that the internal lipids contain the same components as the hair surface lipids suggesting that these lipids are, partly at least, originating from the sebaceous glands. INTRODUCTION Excessive oiliness of hair is a widespread cosmetic problem, especially among young people, and numerous publications address themselves to the quantitative estimation of hair lipids, assuming that it is the sebum quantity that is the governing reason for hair oiliness. At the first glance it seems reasonable to assume that the "external" sebum is the one which is removed by shampooing, as clean hair does not appear oily. On the other hand, shampooing is claimed to remove only 50% of the lipids extractable with ether under mild conditions (1). Probably the missing 50% of the lipids are more strongly absorbed by the hair surface or are covered by the cuticle scales and thus not visible. Although those lipid fractions do not contribute directly to the visible oiliness of the hair, they abridge the period of reoiling by occupying "storage capacity" in and on the hair. Therefore, they should logically be considered as part of the external sebum and should be removed by the extraction method to be developed. 317

318 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Furthermore, sebum quantity is not likely to be the only factor in perception of oiliness. Apart from some physical properties of the hair itself (e.g., fiber diameter, curliness, softness), differences in the physical properties of the sebum (e.g., melting point, viscosity, surface tension) caused by the different chemical composition might also play a role by influencing the velocity of spreading on the hair surface (2,3), the stickiness and the postulated limitation of sebum production by the feed back mechanism (4). Such correlations between lipid composition and appearance have already been found for skin sebum (5). Therefore, it should be as important to analyse the composition of sebum as to determine its quantity. In an earlier publication (6), a method has been described for the quantitative determination of total amount and composition of sebum lipids in hair extracts, allowing at the same time the preparative isolation of the different lipid groups for further analytical characterization by e.g., gas liquid chromatography/mass spectrosco- py. A prerequisite for obtaining reliable and comparable analytical results with this method is a well defined and reproducible hair cutting and extraction procedure for the isolation of the surface lipids, which should be responsible for the oily appearance of hair. Further investigations were concerned with the detection of carboxylic acids bound to the hair surface as calcium- and magnesium-soaps and of internal lipids, i.e., lipids which are not extractable even with the most intensive shampooing procedure, in this case simulated by solvent extraction under defined conditions. EXPERIMENTAL SOLVENT EXTRACTION OF EXTERNAL LIPIDS Swatches of human hair (batch A, B, and C) were cut to pieces of about 3 mm length. Each of these batches was mixed thoroughly in order to secure homogeneity. 450 mg samples were used for each extraction. For pre-conditioning, some of them were stored at ambient temperature for 2 h at 100% relative humidity (RH). In the initial experiments they were subsequently immersed in 25 ml of the respective pure or water-saturated* solvent** and stirred slightly for 10 min at room temperature. The finally adopted extraction conditions included two 10 min extractions under reflux, each with the 50-fold quantity of H20-saturated ether and two subsequent washings with 10 ml of ether each. The combined extracts and rinsings were filtered through a funnel with a fritted disc No. 3D4, the solvent evaporated, and the residue dried over CaCI2 for 2 h at 10 mm/60øC and subsequently at room temperature till weight constancy. Quantity and composition of the extracted sebum were determined gravimetrically and by high performance liquid chromatography (HPLC) according to reference 6. For the HPLC analyses (6) the free fatty acids in the extracts were methylated with CH2N2 in ether and after addition of an appropriate quantity (c. 15% of extract) of internal standard in CHCI 3 and evaporation of the solvent, the samples were ready for LC analysis. Blind values were obtained from samples prepared in the same way from pure solvents and reagents. *Only in case of CHCI 3: MeOH = 2: 1, 4% of H20 were added. **Solvents were analytical grade and further purified by filtration through an A1203-column.