BACKGROUND: To date, risk assessment following topical exposure to cosmetic/dermatological formulations cannot be precisely evaluated.
OBJECTIVES: To provide a tool for optimization of active permeation into/through skin and for risk assessment.
METHODS: A predictive model was developed for estimating the cumulative mass of a chemical absorbed into and across the skin from a cosmetic/dermatological formulation. Account was taken of (i) the ionization state of the chemical, to correct the skin/vehicle partition coefficient; and (ii) the nature of the cosmetic/dermatological formulation. Three specific assumptions were made: firstly, steady-state transport across the skin was achieved despite application of a finite dose of chemical; secondly, vehicle effects were small relative to the precision of the prediction; and, thirdly, each formulation could be treated as an oil-in-water emulsion, in which only that fraction of the chemical in the aqueous phase was available to partition into the stratum corneum. A database of 101 ex vivo human skin experiments involving 36 chemicals was analysed.
RESULTS: For 91% of the data, the difference between predicted and experimental values was less than a factor 5; when the aforementioned corrections were not used, on the other hand, only 26% of the data was well predicted. The model was successfully applied to predict skin absorption of two compounds not included in the database, for which in vitro percutaneous penetration from cosmetic vehicles have been measured.
CONCLUSION: A model has been developed to predict the mass of a chemical absorbed into and through the skin from a cosmetic or dermatological formulation.