Stratum corneum is an effective barrier to TiO2 and ZnO nanoparticle percutaneous absorption.
Level 4 - case-series / case-control
Experimental human in vivo study using skin biopsies without a randomized clinical control group.
PubMed 19690452 · doi:10.1159/000235554
What was done
Researchers evaluated the localization and percutaneous absorption of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles from three sunscreen formulations applied in vivo to human skin. Formulations included a hydrophobic test vehicle containing coated 20-nm TiO2 nanoparticles and two commercial sunscreens containing TiO2 alone or combined with ZnO. Applications were performed under open conditions (2 hours) and occluded conditions (48 hours) on normal and altered skin. Transversal skin cryosections obtained from biopsies were analyzed using nuclear microscopy techniques to map Ti and Zn nanoparticle distributions.
What was found
The abstract reports no numeric concentrations, percentages, or detection thresholds. Following 2 hours of exposure to normal human skin, detectable TiO2 and ZnO were present only at the skin surface and in the uppermost stratum corneum, with deposition in pilosebaceous follicular openings. Deeper epidermal layers were devoid of TiO2 or exogenous ZnO even after 48 hours of occluded exposure. Penetration into viable skin tissue was not detected.
Why it matters
These findings suggest that intact stratum corneum prevents systemic or viable-cell exposure to TiO2 and ZnO nanoparticles from topically applied sunscreens under realistic consumer use conditions.
Limits
The abstract omits the number of human subjects or skin samples tested, lacks numerical data and analytical detection limits, and does not provide specific outcome details for the altered skin mentioned in the study objective.
Cited by
- supports Non-nanoparticle zinc oxide sunscreen stays on the skin surface and is not absorbed into the bloodstream.