ABSTRACT
There are different approaches to modulate the penetration of active ingredients into the skin, i.e., either to increase the penetration or to minimize it. In general, increase in penetration is desired in case of pharmaceutical actives, either focusing the drug in the upper skin layer for local treatment or to achieve permeation of the skin leading to systemic absorption. A classical example for the latter case is nitroglycerine creams, finally leading to the development of transdermal patches. For cosmetic actives, the penetration to only a limited degree is desired to ensure that the active creates only cosmetic effects and do not lead to a pharmaceutical treatment of the skin. In case of sunscreen formulations, the penetration should be minimized to avoid irritations of the skin or other side effects, such as allergic reactions (1,2). Therefore, depending on the purpose of the topical formulation different requirements might be fulfilled by the dermal formulation.
