Five adult volunteers had coated and uncoated zinc oxide nanoparticles (10 % w/w in caprylic/capric triglyceride, 2 mg/cm2) applied hourly for six hours and daily for five days. Multiphoton imaging showed the particles stayed on the skin surface and in furrows and did not enter the viable epidermis or cause cellular toxicity. Zinc-ion staining of excised skin showed slightly elevated zinc ions in the viable epidermis.
Key numbers
Results, PDF p. 2, viable-epidermis zinc oxide signal as % of topical dose, mean (95 % CI), five volunteers:
| Schedule | Uncoated | Coated | Untreated | Vehicle |
|---|---|---|---|---|
| Hourly x6 | 0.48 (-0.6 to 1.57) | 0.71 (-1.0 to 2.4) | 0.06 (0.03-0.1) | 0.08 (0-0.15) |
| Daily x5 | 0.1 (0.07-0.14) | 0.08 (0.06-0.09) | 0.09 (0.06-0.1) | 0.08 (0.04-0.12) |
None of the treated values differed significantly from controls.
Methods (brief)
Commercial uncoated and triethoxycaprylylsilane-coated zinc oxide nanoparticles; multiphoton tomography with fluorescence lifetime imaging in vivo; ZinPyr-1 staining of excised skin. Corresponding author: m.roberts@uq.edu.au.
Evidence fitness
Supports the conclusion that zinc oxide nanoparticles do not enter viable epidermis of intact adult skin under repeated use, while some zinc ions do. It gives no elemental mass balance and does not address metal impurities.
Limitations
Five adults, forearm skin, a simple oil vehicle rather than a finished sunscreen, and negative lower confidence limits that reflect small-sample intervals.
Related evidence
- Human Epidermal Zinc Concentrations after Topical Application of ZnO Nanoparticles in Sunscreens
- Should nanoparticles be used in sunscreens?
- Zinc
Update history
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