A HUMAN INVIVO METHOD FOR ASSESSING REDUCTION OF THE IRRITATION POTENTIAL OF SODIUM LAURYL SULFATE BY MILD SURFACTANTS - VALIDATION WITH ANETHER CARBOXYLATE WITH 2 DIFFERENT DEGREES OF ETHOXYLATION

An in vivo method devised for studying reduction of the irritation pot ential of sodium lauryl sulfate (SIS) by added surfactants was validat ed using an ether carboxylate with two different degrees of ethoxylati on. The method involved a two-hour occlusive patching procedure on fiv e consecutive days accompanied by multiple instrumental measurements. Various aqueous solutions combining 1.0% SIS with sodium laureth-5 car boxylate (SLEC-5) or sodium laureth-13 carboxylate (SLEC-13) in molar ratios from 1:0.08 to 1:1.00 were applied using Hill Top(R) chambers o n the panelists' lower backs. Measurements of transepidermal water los s, electrical conductance, laser Doppler flowmetry and skin color refl ectance were performed. In addition, the skin was visually graded for erythema. A data reduction system was devised to handle the large numb er of data points. To accomplish this, the degree of skin response cau sed by 1.0% SLS was used as the reference standard. For each evaluatio n method, on each day and for each panelist, the molar ratio which ind uced greater-than-or-equal-to 50% of the SLS value was used to derive a mean molar ratio for each group of six panelists. The mean molar rat io (i.e., the proportion of SLEC-5 or -13 to ''neutralize'' 1.0% SIS) reflects the effectiveness of che ether carboxylate in reducing the SL S irritancy potential. The molar proportions that induced signs of irr itation changed with successive patch applications, and increasing amo unts of the ether carboxylate were needed to overcome the effects of S IS. Although both SLEC-5 and -13 exerted beneficial effects in reducin g SIS irritancy potential, it was clearly demonstrated that SLEC-13 (i .e., the higher ethoxylated surfactant) was more effective in modifyin g the irritancy potential of SIS than SLEC-5. The various evaluation m ethods generally showed good correlation but differed somewhat in sens itivity. The method appears to provide the requisite specificity and s ensitivity to discriminate differences in the irritancy potential of s urfactant mixtures containing SIS.