Does epidermal turnover reduce percutaneous penetration?

Purpose. After its removal from the skin surface, chemical remaining within the skin can become systemically available. The fraction of chemical in th e skin that eventually enters the body depends on the relative rates of per cutaneous transport and epidermal turnover (i.e., stratum corneum desquamat ion). Indeed, some investigators have claimed that desquamation is an effic ient mechanism for eliminating dermally absorbed chemical from the skin. Methods. The fate of chemical within the skin following chemical contact wa s examined using a mathematical model representing turnover of and absorpti on into the stratum corneum and viable epidermis. The effects of turnover r ate, exposure duration, penetrant lipophilicity, and lag time for chemical diffusion were explored. Results. These calculations show that significant amounts of chemical can b e removed from skin by desquamation if epidermal turnover is fast relative to chemical diffusion through the stratum corneum. However, except for high ly lipophilic and/or high molecular weight (>350 Da) chemicals, the normal epidermal turnover rate is not fast enough and most of the chemical in the skin at the end of an exposure will enter the body. Conclusions. Epidermal turnover can significantly reduce subsequent chemica l absorption into the systemic circulation only for highly lipophilic or hi gh molecular weight chemicals.