Topical treatment of skin diseases with bioactive inorganic nanomaterials: beyond drug delivery

Topical treatment of skin diseases, an option avoiding inconveniencies of systemic administration, is hampered by skin impermeable cornified structure, which constitutes a formidable barrier to drug access. Important improvements are expected from the use of nanomaterials, either organic or inorganic; in fact, their specific physicochemical characteristics allow them to some extent crossing the skin barrier. Nanomaterials suitability to bind and deliver molecular drugs can thus permit unexpected penetration of conjugated drugs into the skin, strongly improving efficiency of topical treatments. Furthermore, when in the 1–100 nm size range, several inorganic metal/metal oxide nanoparticles (e.g., gold, silver, cerium oxide) notably exert intrinsic bioactivities that are functional for treating skin diseases (e.g., anti-inflammatory, antibacterial, antioxidant), or possess peculiar optical properties enabling them acting as novel photosensitizers for cytotoxic therapies against skin cancer. We critically review here studies describing how inorganic nanoparticle features may represent a potential breakthrough for skin disease treatment.