Comparative study of experimental and theoretical curves obtained by plotting transepidermal water loss against stratum corneum thickness in man, shows that every layer in the stratum corneum acts as part of the epidermal barrier to water loss. Another function of the stratum corneum is to decrease the cutaneous penetration of topical corticosteroids like difluprednate and to modify their bioavailability (‘corticosteroid reservoir’) Our data suggest that variations in stratum corneum thickness between subjects explain variation of transepidermal water loss and sensitivity difluprednate, as there is a close relationship between these two parameters. It is then conceivable that the phototype has clinical implications if there really exists a relationship between phototype, stratum corneum thickness and sensitivity to stero