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Synopsis The bio-mechanical properties of the stratum corneum are of great importance for the subjective perception of skin conditions (dry vs. normal), as well as for its multiple functions. The recently developed Gas Bearing Electrodynamometer allows us to measure objectively the viscoelastic properties of the stratum corneum in vivo and to evaluate, in terms of skin softness, the changes of this parameter induced by the application of emollients. The principle of the technique, as designed by Christensen et al., is briefly described in context with our results. During the probe movement, there was a modification of the skin surface relief: compression of the skin furrows ahead of the moving probe, and extension-flattening of the relief behind the probe. The variations of the skin softness were studied in context with the reproducibility of the measurements: the coefficient of variation was found to be about 3%. Considerably higher variations were found as related to: the anisotropy of the skin surface relief, various areas of the body, and individual differences. The effects of emollients and water on the skin softness were studied. Water had a clear effect but of very short duration (around 10 minutes). Water-containing emollients of the type o/w emulsions displayed a distinct long-lasting effect (followed up to 6 hours). Its magnitude was generally higher than that obtained with w/o emulsions. It was found that the emollient's non-volatile components (oil phase) play an important role in the product's softening effect. In conclusion, results to date have established this technique as a promising tool for studying skin softness in general, and effects of topical applications, new formulae and specific ingredients in particular.

Synopsis An objectivised sensorial method for evaluating the effects of shampoos on the appearance and manageability of the hair is described. Two different shampoos for greasy hair were applied twice weekly for a period of 4 weeks to the right and left sides (split-head tests) of six subjects having greasy hair, the same shampoo being applied to the same side. A trained observer used a continuous rating scale to assess nine cosmetic parameters; overall assessments by observer and subjects were noted. Evaluations were made immediately after and at various intervals following shampoo. The data were presented in 'profile graphs' and evaluated statistically. Shampoo A was found to be significantly better (P < 0.05) than shampoo B for all parameters immediately after shampoo and for six parameters after 1 day. The differences between A and B were no longer significant after 2 days, and only marginal differences were noted after 3 and 4 days. Analysis of the results of forty additional split-head tests carried out with ten different shampoos revealed interdependence (P < 0.01) between some parameters. Our results show the elective action of shampoos on the cosmetic parameters, the duration and limits of this action, and the interdependence between certain parameters.

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Synopsis A multi-technique evaluation of the hair regreasing process is described. Preliminary experimentation in vitro was followed by a long-term in vivo study conducted on a single subject having greasy hair. First, a shampoo for very greasy hair and one for dry hair were applied to the left and right sides of the head respectively (split-head test) for 7 weeks; then a shampoo for greasy hair was applied to the entire head (whole-head test) for 5 weeks. Three parameters were studied: (1) hair spacing, determined by means of a special device; (2) regreasing of individual hairs, measured using the contact-reprint technique; (3) the amount of sebum extracted from individual hairs, performed by g.l.c. determination of squalene. Results obtained during the split-head period showed that the shampoo for very greasy hair showed higher average hair spacing, slower progression of regreasing, and better sebum-removal efficiency when compared to the shampoo for dry hair. During the whole-head test period with one shampoo, results showed that there was consistent asymmetry as regards hair spacing and progression of regreasing. These results support our hypothesis concerning the role of interfacial forces in the hair regreasing process.