OBJECTIVE This report examines our present knowledge of the epidermal permeability barrier as it pertains to irritant contact dermatitis and discusses how altered barrier function may affect the clinical manifestations of irritant contact dermatitis in the aged. CONCLUSIONS Altered barrier function affects the ability of an irritant to penetrate the stratum corneum and produce deleterious effects on both stratum corneum and epidermis. Moreover, a damaged epidermis can be expected to produce a defective stratum corneum, thus resulting in a vicious cycle. Furthermore, although basal transepidermal water loss has traditionally been used as an assessment of barrier function, evidence suggests that dynamic tests of barrier function are more reliable indicators of barrier function in the clinical setting of additive, repetitive, or chronic insults. Finally, barrier disruption per se has now been shown to produce both a cytokine response and an increase in epidermal Langerhans' cell density. Thus, barrier disruption not only alters penetrance of contactants, but also may prime the inflammatory response. Studies of aged epidermal permeability barrier function provide a greater understanding of the modified response to irritants in the aged.