28 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In x R 2, 0.87 F ß 5:• EACH POINT IS AN AVERAGE OF 6 REPLICAS I I I I I I I I I I I o IO 2o :•o 4o 50 60 7o 80 90 IOO TIME { HOURS} Figure 8. Rate of EM thickness changes in water. (19), but leveling occurs with hair, water must produce structural changes in the EM matrix that do not occur in hair. This may be due to removal of water soluble organic matter from EM which is important to the corneum matrix in the thickness dimension, but not in the CW length dimension. SURFACTANTS Epidermal membrane is more responsive than hair to swelling induced by anionic surfactant, and it is highly responsive in both CW length and thickness dimensions (Table V). In fact, the increase in CW length of EM, after 24 hours in 0.069 M sodium lauryl sulfate (SLS), is about 30 percent, while the swelling of human hair in either diameter or length, under the same conditions, is less than 7 percent. Spei, Stein, and Zahn (24) have examined the low angle x-ray scattering of mohair fibers treated with alkyl sulfate surfactants, and they conclude that these species initially Table III Swelling of Hair and EM in Liquid Water at 24 Hours CW Length* Thickness** EM q- 11% + 2O0% Length* Diameter*** Hair + 1.3% + 15.7% *Average of 10 replicas **Average of 30 replicas ***Calculated from CW length (N = 10) and weight measurements (N = 24)

SWELLING OF EPIDERMAL MEMBRANE 29 Table IV Amino Acids of Human Hair and EM Amino Acid Residues/100 Residues Amino Acid EM Hair Aspartic Acid 8.3 6.0 Threonine 3.9 7.3 Serine 11.4' 11.4' Glutamic Acid 12.3 13.9 Proline 2.6 8.1 Glycine 18.8 5.9 Alanine 5.5 4.7 Cystine 0.9 11.6 Valine 4.8 6.3 Methionine 0.8 1.4 Isoleucine 3.7 2.9 Leucine 7.5 6.7 Tyrosine 3.4 2.3 Phenylalanine 3.1 1.6 Histidine 2.0 0.9 Lysine 5.6 2.4 Arginine 5.4 6.7 = 100.0 = 100.1 Each determination is an average of 4 replicas. *No significant difference, all other amino acids are significantly different between substrates beyond the = 0.01 level. Conversion to micromoles amino acids/gm indicates that these amino acids represent 95% of the hair but only 66% of the epidermal membrane, therefore EM contains more than 30% matter not convertible to amino acids. Table V Comparative Swelling of Human Hair and Epidermal Membrane Human Hair Epidermal Membrane Length Diameter* CW Length** Thickness*** Water (24 Hours) (From dry state) + 1.3% + 15.7% + 11% + 200% 2% SLS•: (1 Hour) -- - + 14% + 191% (24 Hours) + 0.2% + 6.6% + 30% -- (NSD) Formic AcidJ (97%) (30 Min) + 2.1% + 24% + 50% + 130ø3 *Average of 10 to 30 replicas. **Average of 10 or more replicas. ***Calculated from CW length (N = 10) and weight gains (N = 6 to 24) measurements. :•kll values are expressed as percent increase above water value at 24 hours. SLS = Sodium lauryl sulfate NSD = No significant difference