A clinical study in the Journal of Investigative Dermatology found that zinc oxide nanoparticle sunscreens do not penetrate living skin cells or cause toxicity, supporting their safe daily use.
Why Zinc Oxide Nanoparticles Matter
Zinc oxide (ZnO) is a widely used broad-spectrum sunscreen filter that protects against both UVA and UVB radiation. In nanoparticle (NP) form, ZnO provides transparent coverage, making sunscreens more cosmetically appealing compared to older, opaque formulations.
However, concerns have persisted that ZnO nanoparticles might penetrate the skin barrier and cause oxidative stress or DNA damage, as some in vitro studies suggested.
What This Study Found
A 2019 clinical study published in the Journal of Investigative Dermatology directly tested the safety of ZnO nanoparticle sunscreens in humans.
Study design:
- Participants: 5 healthy volunteers.
- Exposure: Sunscreens containing coated and uncoated ZnO nanoparticles were applied repeatedly (hourly over 6 hours, and daily for 5 days).
- Methods: Advanced imaging (multiphoton tomography and fluorescence lifetime microscopy) tracked nanoparticle location and assessed skin cell health.
Key findings:
- Nanoparticles stayed on the surface: ZnO NPs accumulated on the stratum corneum (outer skin layer) and in skin furrows, but did not penetrate into the viable epidermis.
- No cellular toxicity: Skin cells showed no structural or metabolic changes, meaning no evidence of toxicity or oxidative stress.
- Zinc ions, not particles, entered the skin: Some soluble zinc ions were detected in the epidermis, but without harmful effects.
Why This Matters for Sunscreen Safety
This study supports previous evidence showing that ZnO nanoparticles remain on the skin surface and are safe for topical use.
Given that regular sunscreen use significantly reduces skin cancer risk, experts emphasize that the benefits of nanoparticle sunscreens far outweigh theoretical risks.
Bottom Line
Zinc oxide nanoparticle sunscreens are safe for repeated human use. They do not penetrate living skin cells or cause toxicity, making them an effective and reliable option for UV protection.
References
- Mohammed YH, et al. Support for the Safe Use of Zinc Oxide Nanoparticle Sunscreens: Lack of Skin Penetration or Cellular Toxicity after Repeated Application in Volunteers. J Invest Dermatol. 2019;139(2):308-315. doi:10.1016/j.jid.2018.08.024 .
Zehn Skin and Health 
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