JOURNAL OF COSMETIC SCIENCE 450 both covalently bound and non-covalently bound, such as palmitic, stearic, oleic and palmitoleic acids, were not quantitated and were found in signifi cant quantities in other studies (13,34,35,42,56). Cholesterol sulfate was also not determined in this effort by Masukawa et al. Logan et al. (56) analyzed human hair by extracting it with a chloroform/methanol azeo- trope for fi ve hours after surface lipids had been removed with t-butanol and heptane, and they found 23% palmitic, 25% palmitoleic, 4% stearic, and 13% oleic acids, as well as other fatty acids. These are all non-covalently bound fatty acids, with 39% of the total fatty acids being unsaturated (palmitoleic and oleic acids, but it is possible that other unsaturated fatty acids were present). Weitkamp et al. (61), by analysis of solvent-extracted lipids from pooled adult Caucasian human hair clippings, found 51% of the total fatty acids to be unsaturated, with palmitoleic and oleic acids as the principal unsaturated fatty acids, but other unsaturated fatty acids were found in these extracts. Masukawa et al. (57) initially shampooed the hair and then washed it with hexane, allow- ing a fi ve-minute incubation time. The hexane wash was determined by plotting the amount of lipid extracted versus the square root of the time of the hexane wash. The time that diffusion of lipids from the interior of the fi ber began was determined graphically, a reasonable approach to removing external lipid soils from the fi bers, presumably leaving most of the internal and structural lipids in the hair. The lipids removed were separated into eight groups by Masukawa et al., and their data are summarized in Table II. These data show that approximately 58% of the total lipids in hair under these conditions are fatty acids, some covalently bonded, with others exist- ing as free and non-covalently bound fatty acids. The total fatty acids found were 14.4 mg/gm of hair, but only 0.3 mg/gm hair of 18-MEA were found. Wertz and Downing (34) found 1.31 to 2.1 mg/gm of 18-MEA in four different human hair samples (three from individuals and one pooled hair sample, presumably Caucasian hair) and in a later paper (35) cited 4.0 mg/gm total integral (covalently bound) fatty acids with 40.5% as 18-MEA for human hair or 1.6 mg/gm 18-MEA. Since most 18-MEA estimates in wool fi ber are close to 1 mg/gm or higher and human hair contains more cuticle layers than wool fi ber, one would expect more covalently bound fatty acids in human hair than in wool Table II Lipids in Human Hair, from Masukawa et al. (57) and Wertz and Downing (35) Type of lipid mg/gm hair Percentage of total lipid Hydrocarbons 2.4 9.7 Squalene 0.7 2.8 Wax easters 4.9 19.8 Triglycerides 0.5 2.0 Total fatty acids 14.4 58.1 (58)** Total covalent fatty acids — (4.0)* Cholesterol 1.3 (0.6)* 5.2 Cholesterol sulfate — (2.9)* Ceramides 0.29 (0.5)* 1.2 18-MEA 0.30 (1.6 )* 1.2 Totals 24.79 100% *Data in parenthesis by Wertz and Downing (35), not in parenthesis by Masukawa et al. (57). **See Logan et al. (56) for a breakdown of the actual fatty acids in human hair.

CELL MEMBRANE COMPLEX 451 fi ber. Masukawa did not list amounts for total covalently bound fatty acids, only for 18- MEA. Therefore, I will use the data for Wertz and Downing (35) for total covalently bound fatty acids. Since Masukawa et al. (57) found 14.3 mg/gm total fatty acid, but did not determine the total covalently bound fatty acids, and Wertz and Downing found 4 mg/gm total cova- lently bound fatty acids, then the Masukawa et al. fi nding most likely represents or is closer to the total amount of non-covalently bound fatty acids in human hair. Therefore, if we assume human hair has approximately 14 mg/gm of non-covalently bound fatty acids and we assume about ½ the equivalent amount of free lipid in the cuticle relative to cova- lently bound fatty acid, this provides 2 mg/gm of free fatty acid in cuticle layers and leaves about 12 mg/gm of non-covalently bound fatty acids. If we then assume 2 mg/gm of fatty acid as intracellular lipid, that leaves 10 mg/gm of fatty acids in the cortex–cortex CMC. Therefore, with these approximations, about 10 mg/gm of fatty acids will exist in the “bilayers” of the CMC of the cortex of human hair along with cholesterol, cholesterol sulfate, and ceramide, (see Figure 3). Wertz and Downing (35) also found cholesterol (0.6 mg/gm), cholesterol sulfate (2.9 mg/gm), and ceramides (0.5 mg/gm) in their alkaline hydrolysates from human hair after removal of all free lipids by chloroform–methanol extraction. These same scientists also found these same lipid components in hair from sheep, dogs, pigs, cattle, and humans: cholesterol (0.3–1.4 mg/gm), ceramides (0.6–1.4 mg/gm), and cholesterol sulfate (0.7– 3.3 mg/gm) (36). Examination of these data from different laboratories suggests the fol- lowing ingredients in these approximate ratios as the principal components of the bilayers of the cortex–cortex CMC for human hair: Lipid component Approximate amount Approximate relative amount Fatty acids 10 mg/gm hair 10 Cholesterol sulfate 0.7 to 3.3 mg/gm 2 Cholesterol 0.6 to 1.2 mg/gm 1 Ceramides 0.6 to 1.4 mg/gm 1 After shampooing an appreciable amount of free lipid remains on the hair surface. Shaw (62) sug- gested that washing hair with ether or shampoos in a one-step application leaves virtu- ally the entire hair surface free of lipid (removable by surfactants or solvent) and that differences in cleaning effi ciencies of surfactants relate to the amounts of internal lipid removed. Recent XPS data show that shampooing does remove some free lipid from the surface of hair, but even after shampooing a signifi cant amount of free lipid remains in the surface layers, that is in the top 3 to 5 nm (58). Free lipid in surface layers affects the isoelectric point of wool and hair. Capablanca and Watt (63) examined wool fi ber that had been washed with detergent (Lissapol) and extracted with various solvents using a streaming potential method to estimate the effect of free-lipid (non-covalently bound fatty acids) in the surface layers on the isoelectric point of wool fi ber. These scientists found an appreciable effect of free lipid on the isoelectric point. The surfactant-washed wool (containing the most free lipid) provided an isoelectric point of These ratios are most likely not exact, but they show a large amount of fatty acid followed by cholesterol sulfate and smaller amounts of cholesterol and ceramide.