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.