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j. Soc. Cosmet. Chem., 48, 159-163 (May/June 1997) Letters to the Editor TO THE EDITOR: The authors of the article "Interactions of cleansing bars with stratum corneum proteins: An in vitro fluorescence spectroscopic study" (Mukherjee et at., J. Soc. Cosmet. Chem., 46, 301-320, 1995) claim that sodium lauroyl isethionate (SLI) surfactant and a cleansing bar containing SLI deposit less surfactant residue on stratum corneum than sodium laurate, sodium lauryl sulfate (SLS), triethanolamine (TEA)-laurate, and a cleansing bar containing TEA soap. The results are based on the assumption that when binding to stratum corneum proteins, surfactants will displace a previously bound fluorescent marker, -12-(9-anthroyloxy)-stearic acid (ANS), and will subsequently cause a decrease in fluorescence of ANS. Unfortunately, there are many omissions and inconsistencies throughout this article that cause the proported results and conclusions to be highly controversial. We will confine our comments to a few main points. First, the authors assert that anionic surfactants do not appreciably solubilize ANS because ANS exhibits "low" fluorescence in solutions of SLS and SLI, compared to a solution of a non-ionic surfactant. Remarkably, ANS solubility interactions with Na- laurate and TEA-laurate, two surfactants mentioned prominently in the article, were not disclosed by investigators. Data from our laboratory, however, show that ANS has a 2 x greater fluorescence intensity in a solution of TEA-laurate than with SLS and SLI. Because TEA-laurate is more likely to solubilize ANS, less ANS will adhere to the skin, more of the ANS will be rinsed from the stratum corneum, and a weaker fluorescence will occur than with SLI, a phenomenon reported in the article. The authors should be aware that if ANS is to be used as a fluorescent marker in surfactant studies, it should have equal and very little, if any, interaction with all test surfactants this was obviously not the case in the Mukherjee et at. study. The authors claim to validate their ANS displacement results by correlating ANS displacement by surfactants with radiolabeled surfactants binding to the stratum corneum. This correlation offers no conclusive evi- dence because results for radiolabeled TEA-laurate binding were not disclosed at either the l-rain or 1-hr time points. In addition, results of radiolabeled Na-laurate binding were only shown at the 1-hr time point, yet the authors conclude that the two events (ANS displacement and binding of radiolabeled surfactant) are linked. Another major defect in this paper is the dismissal by the authors of the contribution of pH to the fluorometric methodology. Previous literature (1,2) reports that the pH of the test solution (e.g., surfactant) greatly contributes to ANS fluorescence, with a higher pH causing a decrease in fluorescence and a lower pH greatly enhancing fluorescence. The 159