A strategy for skin irritation testing.
Skin irritation safety testing and risk assessment for new products, and the ingredients they contain, is a critical requirement before market introduction. In the past, much of this skin testing required the use of experimental animals. However, new current best approaches for skin corrosion and skin irritation testing and risk assessment are being defined, obviating the need for animal test methods. Several in vitro skin corrosion test methods have been endorsed after successful validation and are gaining acceptance by regulatory authorities. In vitro test methods for acute, cumulative (repeat exposure), and chronic (prolonged exposure) skin irritation are under development. Though not yet validated, many are being used successfully for testing and risk assessment purposes as documented through an expanding literature. Likewise, a novel acute irritation patch test in human subjects is providing a valid and ethical alternative to animal testing for prediction of chemical skin irritation potential. An array of other human test methods also have been developed and used for the prediction of cumulative/chronic skin irritation and the general skin compatibility of finished products. The development of instrumental methods (e.g., transepidermal water loss, capacitance, and so on) has provided the means for analyzing various biophysical properties of human skin and changes in these properties caused by exposure to irritants. However, these methods do not directly measure skin inflammation. A recently introduced skin surface tape sampling procedure has been shown to detect changes in skin surface cytokine recovery that correlate with inflammatory skin changes associated with chemical irritant exposures or existing dermatitis. It holds promise for more objective quantification of skin irritation events, including subclinical (sensory) irritation, in the future.