Skin-blood partitioning, process

Absorption Across the Skin. An aqueous carrier may be used for a variety of dermal products. In fact, carriers can be designed to limit the transportation of the penetration of the active ingredient (such as an insect repellent), if the desired effect is to keep the activity on the surface of the skin. Once again, however, only those materials that are dissolved will be available for penetration across the skin to gain access to the systemic circulation. For almost all chemicals in or about to enter commerce, dermal penetration is a passive process. The relative thickness of the skin makes absorption (into the systemic circulation) slower than the absorption across the GI or pulmonary barriers. This is compounded by the fact that the stratum comeum ftmction is to be impervious to the environment. One of the skin s major functions is protection from infection. Once a chemical penetrates into the dermis, it may partition into the subcutaneous fat. Essentially, absorption across the skin is a two-step process with the first being penetration and deposition into the skin and the second being release from the skin into the systemic circulation. The pattern of blood levels obtained via dermal penetration is generally one with a delayed... 

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