Relative Penetration of Zinc Oxide and Zinc Ions into Human Skin after Application of Different Zinc Oxide Formulations.
Level 5 - mechanism / opinion, no new human data
Ex vivo/in vitro laboratory study on human epidermal tissue
PubMed 26741484 · doi:10.1021/acsnano.5b04148
What was done
Researchers evaluated the epidermal penetration of zinc oxide (ZnO) nanoparticles and their dissolved labile zinc ions across three formulations applied to human epidermis: a suspension in capric caprylic triglycerides (a common sunscreen oil base), an aqueous suspension at pH 6 (matching natural skin surface pH), and an aqueous suspension at pH 9 (where ZnO is stable and epidermal integrity is preserved).
What was found
The abstract reports no numerical data. Across all three formulations, intact ZnO nanoparticles did not penetrate into the intact viable epidermis. However, application was associated with an increased zinc ion fluorescence signal in both the stratum corneum and the viable epidermis, with the highest labile zinc fluorescence observed with the pH 6 aqueous suspension.
Why it matters
These findings demonstrate that while ZnO nanoparticles themselves do not reach viable epidermal layers, surface hydrolysis allows soluble zinc ions to penetrate viable skin tissue, distinguishing particulate absorption from ionic dissolution.
Limits
The study used isolated human epidermis in a laboratory model rather than in vivo human trials under real-world application conditions. The abstract provides no quantitative measurements, sample sizes, donor counts, nanoparticle dimensions, or exposure durations. Systemic circulation and urinary excretion pathways were inferred rather than directly quantified in the reported abstract data.
Cited by
- context Non-nanoparticle zinc oxide sunscreen stays on the skin surface and is not absorbed into the bloodstream.