What did the research discover?
This study investigated how zinc oxide (ZnO) affects the safety and effectiveness of sunscreen ingredients when exposed to UV light. Sunscreens are generally tested based on individual ingredients, but their stability and safety depend on how these ingredients interact in a formulation. Researchers tested five common small-molecule sunscreen formulations and found:
- Without ZnO, the sunscreen mixtures were stable, showing minimal degradation when exposed to UV radiation.
- Adding ZnO (both nano- and micro-sized particles) caused significant degradation of small-molecule UV filters, especially avobenzone, a key ingredient for UVA protection.
- This degradation reduced UVA protection by more than 80%, meaning the sunscreen became less effective at blocking harmful rays.
- The degraded mixtures became more toxic, causing developmental defects in zebrafish embryos, a model commonly used to predict environmental and human toxicity.
- These findings challenge the perception that mineral-based sunscreens (like those with ZnO) are inherently safer than small-molecule sunscreens.
How can I apply this information?
If you use sunscreen with both zinc oxide and small-molecule UV filters, be aware that UV exposure can degrade the ingredients and reduce its effectiveness. To maximize protection, consider:
- Reapplying sunscreen frequently, especially if using hybrid formulations (containing ZnO + organic UV filters).
- Looking for coated ZnO formulations, which may be more stable.
- Checking for broad-spectrum UVA/UVB protection and reading ingredient lists carefully.
This study also highlights the need for better sunscreen formulations that maintain both efficacy and safety, ensuring that UV protection lasts and does not produce harmful byproducts after sun exposure.
Source:
Ginzburg AL, Blackburn RS, Santillan C, Truong L, Tanguay RL, Hutchison JE. Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation. Photochemical & Photobiological Sciences. 2021 Oct;20:1273-85. https://pubmed.ncbi.nlm.nih.gov/34647278/
