Corneosurfametry

This method, recently described [28], investigates the interaction of surfactants with the human stratum corneum. It is performed as follows: cyanoacrylate skin-surface stripping (CSSS) is taken from the volar aspect of the forearm and sprayed with the surfactant to be tested. After 2 hours, the sample is rinsed with tap water and stained with basic fuchsin and toluidine blue dyes for 3 minutes. After rinsing and drying, the sample is placed on a white reference plate and measured by reflectance colorimetry (Chroma Meter® CR200; Minolta, Osaka, Japan).

The index of mildness (CIM = luminacy L*-chroma C*) is taken as a parameter of the irritation caused by the surfactant. This index has a value of 68 ┬▒ 4 when water alone is sprayed on the sample and decreases when surfactant is tested, with stronger surfactants lowering the values. Pierard et al. [29], testing different shampoo formulations in volunteers with sensitive skin, showed that corneosurfametry correlates well with in vivo testing. A significant negative correlation (p < 0.001) was found between values of colorimetric index of mildness (CIM) and the skin compatibility parameters (SCP) that include a global evaluation of the colorimetric erythemal index (CEI) and the TEWL differential, both expressed in the same order of magnitude.

In the same study, corneosurfametry showed less interindividual variability than in vivo testing, allowing a better discrimination among mild products. An interesting finding showed that sensitive skin is not a single condition. Goffin et al. [30] hypothesized that the response of the stratum corneum to an environmental threat might be impaired in different groups of subjects experiencing sensitive skin. Data of the corneosurfametry, performed after testing eight different house-cleaning products, showed that the overall stratum corneum reactivity, as calculated by the average values of the corneosurfametry index (CSMI) and the CIM, is significantly different (p < 0.01) between detergent-sensitive skin and both nonsensitive and climate/fabric sensitive skin as well.

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