Table 5.

The skin absorption studies of NMs

Composite (Size nm)	Module of the study		Outcome	Reference
	In vitro	In vivo
Polystyrene NMs (20–200)	Vertical diffusion cells by whole-width the skin of ear of porcine	Not Reported	The aggregation of NMs in follicular openings	Alvarez-Román et al. (2004)
Titanium Dioxide	Human volunteers—tape stripping	Diffusion cells by human epidermis plus cultivated skin	Microfine titanium dioxide entered through the follicles of hair	Bennat and Müller-Goymann (2000)
Titanium Dioxide (20)	Human volunteers— tape stripping	Static diffusion cells with human skin	Titanium dioxide could not infiltrate into the viable skin layers	Mavon et al. (2006)
Zinc Oxide (15 to 40)	Not Reported	Franz diffusion cells with human epidermis	There were no NMs in the deeper layer of corneum or epiderm	Cross et al. (2007)
Silver (25)	Not Reported	Full-thickness human epidermis with Franz diffusion cells	Penetration may occur via damaged skin	Larese et al. (2009)
4 various formulations comprising Titanium Dioxide	The biopsies of pig skin	Not Reported	Penetration of NMs within granulosum layer through intercellular area	Menzel et al. (2004)
Ellipsoid (4.6) and Spherical QD (12 × 6)	Not Reported	Porcine skin within flow-through cells	Quantum Dots of various forms and surface coatings may enter intact skin in an appropriate dosage (62.5 pmol per cm2)	Ryman-Rasmussen et al. (2006)
Gold (15, 102, and 198)	Not Reported	Franz cells with rat epidermis	The permeability and diffusion coefficient decrease with the increase in the size of gold NMs	Sonavane et al. (2008)