- Active (501)
- Anti-irritant (119)
- Antimicrobial (97)
- Antioxidant (22)
- Colorant/Pigment/Hair Dye (102)
- Conditioner/Moisturizer (261)
- Delivery (161)
- Exfoliant (13)
- Feel Enhancer (187)
- Film-former (15)
- Formulating Aids (137)
- Fragrance (75)
- Preservatives (81)
- Repair (101)
- Rheology/Viscosity Modifier (94)
- Surfactant/Emulsifier (142)
- UV Filter (118)
Build a solid foundation in science, formulation and product development—find out more!
Most Popular in:
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 7 of 13
Deeper penetration into the viable layers of the epidermis was recently investigated by Nohynek et al. who reviewed every available scientific article that describes the skin penetration of titanium and zinc oxide nano-particles.21 The articles that were published between 1996 and 2007 describe the skin penetration of titanium dioxide (with various types of coating) and zinc oxide (uncoated or no information available) of various particle sizes ranging from ultrafine 14 nm to 2 µm with the majority in the 10-100 nm range, using a variety of techniques (mainly in vitro skin penetration but some skin biopsies and skin stripping) on various species (human, rabbit, pig, mouse) on predominantly healthy and occasionally psoriatic skin. While these conditions varied widely, the results were remarkably consistent. "Penetration of particles into the stratum corneum and outer hair follicle; no penetration into living skin" or something similar was concluded roughly 16 out of 20 times.21
Before reaching a general conclusion that titanium dioxide and zinc oxide nanoparticles do not penetrate beyond the stratum corneum, it is necessary to have a closer look at the four papers that reached a slightly different conclusion.
The first is a study of Pirot et al. using zinc oxide (no information on particle coating) of unknown (microfine) particle size on human skin in vitro. Here, 0.34% was absorbed (location not specified) in 72 hr.22
The second study used zinc oxide of various non-specified particle sizes on normal and psoriatic human subjects, where zinc levels were measured after topical application and in vitro on pig skin. No increase in plasma levels was detected in vivo but in the in vitro experiments, skin penetration was less than 1% of the applied dose, whereas most zinc oxide was recovered in the stratum corneum.23
The third study involved again zinc oxide particles, this time of 15-30 nm, using human skin in vitro. Less than 0.03% of the applied zinc was recovered in the receptor solution, whereas no particles were detected in the epidermis or the dermis.24