SKIN IRRITATION BY ANIONIC SURFACTANTS 53 ø+$.0 • -$.0 C8 C10 CISF1 MAP MAP MAP C12 C12 C!2 C!2 C123 C!28 C!2 AS AOS LAS SAS ES ES B CI2 C1214 AGS S B EO CSII Figure 11. Changes in specific rotation of BSA measured at 1.5% concentration of various surfactants. MAP: monoalkyl phosphate, AS: alkyl sulfate, LAS: linear alkyl benzene sulfonate, SAS: paraffin sulfonate, AOS: alfa-olefin sulfonate, ES: alkyl ether sulfate, B: alkyl betain, SB: alkyl sulfobetain, EO: alkyl polyoxyethlene, AGS: alkyl acylglutamate. IN VITRO ADSORBING PROPERTIES It is well known (12) that when certain amounts of surfactants are adsorbed on protein, protein denaturation, namely unfolding of the secondary or tertiary structure, is induced. Thus, the interaction between bovine serum albumin (BSA) and surfactants as evaluated by using the optical rotation technique (13) was investigated as a more sensitive and convenient model for estimating the adsorptive effect of surfactants on Surfact ant no adsorption} Indigo strong staining T reatmen t weak adsorption Camine l Treatment strong adsorption weak staining no staining Na0$5 E=E $0aNa ß indigo. carmine H H a adsorption site Indigo Carmine Figure 12. Theory for in vivo evaluation of adsorbing ability of anionic surfactants by using acidic dye such as indigo carmine.

54 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the skin. Since the changes in specific rotation are mainly due to the unfolding of cr helix which proceeds stepwise following adsorption of surfactants on BSA, measure- ments of the specific rotation of BSA in the presence of surfactants should make it possible to determine approximately the adsorbing capacity. In fact, it has been established that the amount of surfactants adsorbed by callus powder is comparable to Figure 15a. Variation in the amount of adsorbed indigo carmine on forearm skin retroproportionally to the concentration of applied C•2AS using circulation method at 28C. 0.01 means 0.01g/10Oml concentra- tion. 1.0 0.5 C12 AS pH 7.0 10 rain 28Oc 150 ml/min Circulation •.5 1.o 0.5 mes30mpH C12 AS 10ml 7.0 Callus 40Oc 6 hr incubation 0.61 0.62 0j)3 0.•)4 Surfactant COncentration ( mole/1 ) A 0.01 0.02 0.03 0.04 Surfactant Concentration (mole/1) Figure 15b. Adsorption isotherms of sodium lauryl sulfate on human forearm skin in vivo (A) and isolated human callus powder in vitro (B).