Penetration of nanoparticles and nanomaterials in the skin: fiction or reality?

The advent of nanotechnological products in the market, while holding great promise, is raising concerns in consumers. Therefore, this contribution will attempt to compare different particulate formulations and to answer whether their passive penetration into, and potential permeation through the skin may be possible or not. To this end, skin structure, composition, and penetration paths will be concisely reviewed. Parameters generally cited to affect skin absorption will be resumed and commented on from the perspective of potentially penetrating nanosized agents. These sections will provide the basis to understand what is fiction and what is reality.