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Nanotechnology and Skin Delivery: Infinitely Small or Infinite Possibilities?
By: Johann W. Wiechers, PhD, JW Solutions
Posted: December 19, 2008, from the January 2009 issue of Cosmetics & Toiletries.
- Figure 1. Theoretical predictions of particle penetration
- Figure 2. Histological sections demonstrating the penetration depth
- Figure 3. Kinetics of the storage of nanoparticles
- Figure 4.The effect of particle size on the UV attenuating properties of titanium dioxide.
- Figure 5. Schematic representation of the size-dependent occlusive effect of lipid nanoparticles
- Figure 6: Cumulative amount of ketorolac
page 9 of 13
In cosmetics, nanomaterials are predominantly found in sun care products where the optimum particle size for high UVB and UVA attenuation but good transparency in the visible region is between 40 and 60 nm (see Figure 4).29 Such particles are much bigger than the quantum dots of which the skin penetration was described above. Sun care products are normally applied under massage but on human skin in vivo where the hair density is comparable to that on pig skin (average 20 (11-25) hairs/cm2 for porcine skin30 versus 14-32 vellus hairs on human skin).31
Apart from being applied with massage, all other requirements for optimal skin penetration of nanoparticles from sun care products are not met. Based on the "growing body of (experimental) evidence," it is highly unlikely that nanoparticles like titanium dioxide and zinc oxide as used in sun care products will penetrate into the living epidermis.
The Intrinsic Hazard of Nanomaterials in the Living Epidermis
If penetration does in fact occur, what is known about the intrinsic hazard of these nanomaterials? If some nanomaterial is reaching the living epidermis, irrespective of how little, the next issue to address is their intrinsic hazard. Do the few nanoparticles that manage to get into the viable epidermis constitute a health hazard?
Not being a toxicologist, this author must refrain from making conclusive statements on the intrinsic safety of nanomaterials in general, but for sun care, one can rely on the opinions made by the Scientific Committee on Consumer Products (SCCP) and other papers available in the scientific literature. Some recent reviews cited here refer to many other papers that describe the intrinsic safety (i.e., the hazard) of nanomaterials.
A 2007 review concluded that studies on wear debris particles from surgical implants and other toxicity studies on insoluble particles support the traditional toxicology view that the hazard of small particles is mainly defined by the intrinsic toxicology of particles (i.e., their chemistry), as distinct from their particle size.21