Skin occlusion produces profound changes, including hydration status, barrier permeability, epidermal lipids, DNA synthesis, microbial flora, and numerous molecular and cellular processes. It often, but not always, increases percutaneous absorption of applied chemicals. This overview focuses on the effect of skin occlusion on percutaneous absorption.

Background/aims: Skin occlusion may increase percutaneous absorption of applied chemicals, with some exceptions. It also obstructs the normal ventilation of the skin surface and increases stratum corneum hydration and hence compromises skin barrier function. Methods/results: This review focuses the effects of occlusion on skin barrier function, in particularly, as defined with objective skin bioengineering technology. Conclusions: The effects of occlusion on skin barrier function have been defined with various techniques. Optimal hydrocolloid materials can absorb excess water and reduce the unfavourable effects of occlusion.

Transdermal drug delivery is the controlled release of drugs through the skin to obtain therapeutic levels systematically. Several technological advances have been made in the recent decades to enhance percutaneous drug penetration. This overview focuses on the physical, biochemical, and chemical means of penetration enhancement, as well as the classification and mechanisms of chemical penetration enhancers, their application in transdermal drug delivery, and trends and development in penetration enhancement.

The microneedles aid in bypassing the stratum corneum and enhance drug delivery through it. The design of the microneedle influences its delivery capabilities, because the pointed microneedles seem to be less susceptible to clogging during the injection.

Occlusion, widely used to enhance percutaneous absorption of drugs, also increases penetration of other chemicals and antigens, and hence may exacerbate irritant and allergic contact dermatitis. This overview summarizes the adverse effects of occlusion.