In-vivo test methods for evaluating the skin compatibility of personal washing products

It is well known that the cleansing action of detergents is due to their ability to lower surface tension and therefore to remove particles present on the skin surface. Surfactants are usually used at low concentration in water of varying temperature. However, the repetitive use of cleansing products may induce cumulative skin damage due to the irritant potential of the absorbed surfactants. Surfactant-induced irritation is well-documented: when a surfactant interacts with the skin surface, clinically relevant alterations may occur in both epidermis and/or dermis. Such alterations are often subclinical and therefore non detectable by the human eye. However, they can be objectively detected and quantified by non invasive bioengineering techniques: they include measurements of pH, hydration, barrier integrity (transepidermal water loss, TEWL) by evaporimetry; skin surface roughness and scaling by skin replicas and Image Analysis; skin redness by chromametry and superficial blood flow by laser Doppler flowmetry. The association of these techniques to the clinical evaluation has become popular in most common studies for evaluating skin irritation and the tolerability of cleansing cosmetics.