The human body has several semi-open interfaces for direct substance exchange with the environment, i.e. the skin, respiratory tract and gastrointestinal tract (GIT). Skin is the largest primary defense organ in our body and directly comes into contact with many toxic agents. The skin is structured organ comprising three layers: the epidermis, the dermis and

the subcutaneous layer. The strongly keratinized this website stratum corneum acts as the primary protecting layer and may be the rate-limiting barrier to defend against the penetration of most micron sized particles and harmful exogenetic toxicants. Skin exposure to nanomaterials can also occur during the intentional application of topical creams and other drug treatments ( Curtis et al., 2006, Hagens et al., 2007 and Oberdorster et al., 2005b). According to a study by van der Merwe et al. (2009), nanocrystalline magnesium oxide and titanium dioxide applied to dermatomed human skin (as dry powder, water suspension,

and water/surfactant suspension) for 8 h did not show dermal absorption through human skin with intact functional stratum corneum. In another study, Gontier et al. (2008) tested penetration of topically applied titanium dioxide (TiO2) nanoparticles (size range 20–100 nm) in porcine-, healthy human-, and human grafted-skin samples. It was seen that penetration of TiO2 nanoparticles was restricted to the topmost 3–5 corneocyte layers of the stratum comeum. In contradistinction to this finding, there are many reports that show deeper penetration of nanoparticles. PLX3397 purchase Lademann et al. (1999) showed that TiO2 particles could get through the human stratum corneum and reach epidermis and even dermis. Flexing movement of normal skin was shown

to facilitate the penetration of micrometer-size fluorescent beads into the dermis ( Tinkle et al., 2003). Oberdorster et al. (2005b) demonstrated penetration of a variety of nanoparticles in the dermis and translocation to the systemic vasculature via lymphatic system and regional lymph. Further, Ryman-Rasmussen et al. (2006) demonstrated that quantum dots with diverse physicochemical properties could penetrate the intact stratum corneum barrier and get localized within the epidermal and dermal Tacrolimus (FK506) layers. In a clinical study, treatment of burns using nanosilver coated dressings ( Trop et al., 2006) led to abnormal elevation of blood silver levels and argyria (blue or gray discoloration of the skin due to silver accumulation in the body over time which is a ‘cosmetic problem’). Though nanosilver-based dressings and surgical sutures have received approval for clinical application and good control of wound infection is achieved, their dermal toxicity is still a topic of scientific debate and concern. Despite laboratory and clinical studies confirming the dermal biocompatibility of nanosilver-based dressings ( Chen et al.