Occlusion refers to covering skin by tape, gloves, impermeable dressings or transdermal devices. Certain topical vehicles may also act as “occlusive dressings” if they contain fats or chemicals, reducing water loss to the atmosphere. In healthy skin, the stratum corneum typically has a water content of 10-20% and provides a partial barrier against percutaneous absorption of exogenous substances. Occlusion can increase stratum corneum hydration, and hence infl uence percutaneous absorption by altering partitioning between the surface chemical and the skin due to the increasing presence of water, swelling corneocytes and possibly altering the intercellular lipid phase organization, also by increasing the skin surface temperature, and increasing blood flow. Occlusion may enhance drug efficacy.