148 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Surfactants Employed and Their Properties Alkyl Surfactants Distribution (%) pH (1% soln.) MAP TEA-lauryl phosphate %2:100 7.73 SOAP potassium myristate C•2:0.8 10.77 C•4:98.5 %6:0.6 AGS TEA-cocoyl glutamate C•0:1 5.21 C12:55 Cs4:24 C•6:11 C18:9 ES sodium laureth-2 C•2:100 7.05 sulfate SLS sodium lauryl sulfate %2:100 6.34 EVALUATION OF SKIN TIGHTNESS Four ml of each surfactant solution was applied at 5% concentration to facial skin for 10 seconds followed by rinsing 5 times with water. After wiping the remaining water from the face, skin tightness occurring 1 to 5 minutes later was evaluated comparing right and left cheeks which had been treated with two different surfactants. The relative intensity of skin tightness was evaluated according to the following criteria: - (0) no difference in tight sensation, ___ (1) weak difference in tight sensation, + (2) moderate difference in tight sensation, + + (3) marked difference in tight sensation. The data obtained were analyzed statistically by ScheffCs paired comparison method (11) and were expressed as o•, the value of the main effect after significance was confirmed at the 95% probability level. Yard stick, Y0.05 was calculated according to the equation: Y0.05 = q0.05 X/V•/2rm. V• = mean square error, r = number of judges, and m = number of surfactants compared for the purpose of examining all the significant dif- ferences among the obtained main effects. AMINO ACID ANALYSIS Six glass cups were attached to the forearm and 8ml of 1% surfactant solution were applied by shaking the arms for 10 minutes at the rate of 200 times/min (cup-shaking method) (7). Released amino acids with the exception of glutamic acid were measured by amino acid analysis (Hitachi Co. Ltd., KLA-5) after acidification with HCi and removal of the surfactant with 8ml of ether. UROCANIC ACID ANALYSIS In the system described above, amounts of urocanic acid released after washing were measured by means of high pressure liquid chromatography according to the method of Nakamura (12), with slight modification of the column length (4.6mm X 150mm) and elution conditions (0.5M aa2SO4, pH 2.2).

SURFACTANT INDUCED SKIN TIGHTNESS 149 LIPID ANALYSIS It is difficult to directly measure the deffating ability of surfactant by ether extraction of skin before and after washing with surfactant. Furthermore, the amount of total lipids extracted from surfactant solution is not consistent enough for the weight de- termination of defatting. Therefore, released amounts of squalene and cholesterol were estimated as representative of skin lipids in the solution obtained by the cup-shaking method described above. Removal of surfactant from these mixtures was accomplished by incubation with saturated aqueous BaC12 solution for 1 minute and subsequent extraction with 8ml of ethyl acetate containing 2.5mg of C34 hydrocarbon (Wako Chemical Co. Ltd.) as internal standard. The obtained lipids were incubated with ethyl acetate for 10 minutes, centrifuged (3000 rpm for 15 min), and the supernatant was then analyzed by gas chromatography after concentration under N2 gas, according to the method of Abe (13). MEASUREMENT OF ADSORBED AMOUNTS OF SURFACTANTS According to the method of Imokawa (10), 1% aqueous indigo carmine solutions were attached with glass cups for 1 minute to the forearm areas at which the cup shaking method had been applied. Following this treatment, deposited indigo carmine was removed by immersing the forearm 10 times into a water bath at 40øC. Ten minutes after this washing process, the intensity of the indigo carmine on the stained skin surface was evaluted by color difference (Nippon Denshyoku Co. Ltd.) and expressed as AE (calculated by Hunter's color difference formula). MEASUREMENT OV SKIN GLOSS The appearance of gloss on the surface of the cheek skin was measured at a 75 ø angle with a digital gloss meter (Nippon Denshyoku Co. Ltd.). RESULTS CLINICAL ASPECTS OF TIGHTNESS The clinical appearance of facial skin showing a high degree of tightness is characterized by the occurrence of high gloss and smoothness of the skin which occurs approximately 1-5 minutes after washing with surfactant (Figure 1). -. • •. } --s . . . . .... Figure 1. Clinical appearance of male cheek skin before (left) and after (right) f•e washing with 5% SOAP solution. Abnormal gloss and smoothness of skin surface structure were seen a few minutes after washing.