Self-perceived sensory responses to soap and synthetic detergent bars correlate with clinical signs of irritation.

BACKGROUND: Epidemiologic studies indicate that after using soaps and other personal care products, many consumers experience irritation. In 50% of the cases the feelings of skin dryness, itching, and stinging occur in the absence of visible signs of irritation. OBJECTIVE: We sought to determine the relation between self-perceived sensory responses of panelists to cleansing products and clinical signs of irritation. METHODS: A combination of exaggerated arm-washing methods was designed to induce clinical signs of irritation with psychometric techniques developed to quantify sensations. RESULTS: Two studies demonstrated that panelists could reproducibly differentiate between products on the basis of the sensations they felt and that there was a significant correlation (frequently r > 0.80) between these and the observable signs. In the case of skin dryness panelists differentiated products several washing cycles before observable differences were detected. CONCLUSION: Sensory evaluations of irritation yield additional information on soap and detergent irritancy beyond clinical observations and expand understanding of the irritation process.

Sequential order of skin responses to surfactants during a soap chamber test.

Differences in the response of distinct layers of the skin to surfactants were probed using a modification of the Frosch and Kligman soap chamber test. Soap and other surfactant-containing cleansers were applied to the skin for 2 consecutive days. Transepidermal water loss showed that the stratum corneum is readily damaged even by a mild insult when no erythema is induced. A more severe treatment, such as 24-h exposure to a 5% soap solution, induced the maximal level of barrier damage but a submaximal level of erythema. Even 2 days of exposure to 5% soap does not elicit a maximal erythema response. These results suggest that the stratum corneum is more readily damaged than the dermis, which is not unexpected because the stratum corneum is the initial point of contact between surfactant and skin. Furthermore, this study indicates that for discriminating among mild products, when a small degree of irritation is induced, the most effective measure is stratum corneum damage assessed by evaporimetry. However, for evaluating more irritating products, erythema is probably the more discriminating evaluation technique.

Ethoxylated alcohol (Neodol-12) and other surfactants in the assay of protein kinase C.

Most commonly used surfactants were found to be inhibitors of partially purified rat brain protein kinase C at or above their critical micellar concentrations (CMC). These include sodium lauryl sulfate, deoxycholate, octyl glucoside, dodecyl trimethylammonium bromide, linear alkylbenzene sulfonate and Triton X-100. Several detergents, including the nonionic surfactants digitonin and Neodol-12 (ethoxylated alcohol), did not inhibit protein kinase C activity, even at concentrations greater than their CMC, while the anionic surfactant, AEOS-12 (ethoxylated alcohol sulfate), inhibited enzyme activity only slightly (less than 8%). Since these latter surfactants have little or no inhibitory effect on protein kinase C, they may be of value in solubilizing cells and tissues for the determination of enzyme activity in crude extracts. Among the detergents tested, sodium lauryl sulfate and linear alkylbenzene sulfonate significantly stimulated protein kinase C activity in the absence of phosphatidylserine and calcium. This was found to be dependent on the presence of histone in the protein kinase C assay. These detergents failed to stimulate protein kinase C activity when endogenous proteins in the partially purified rat brain extracts were used as the substrate. Our results indicate that activity of protein kinase C can be modified by the conditions of the assay and by the detergents used to extract the enzyme.