The Hidden Dangers of Zinc Oxide Sunscreen
By Chris Brown
When I was a young surfer in California, zinc oxide sunscreen sticks were all the rage. It was common to see the signature white streaks of zinc oxide along fellow surfers' noses and upper cheeks. When it hit the market, zinc oxide sunscreen was praised for its novel ability to block an extremely wide range of sunlight's cancer-causing UVA and UVB rays for long periods of exposure. However, in recent years, research has come to light that zinc oxide may do more harm than its sun protecting good.
How Does Zinc Oxide Protect From UV Radiation
As opposed to traditional sunscreen, zinc oxide does not simply absorb UV radiation before it reaches the skin. Instead, it creates a physical barrier between the skin and sunlight that scatters ultraviolet light. This accounts for the traditional white color of zinc oxide sunscreens (as the visible light is scattered alongside the UV rays, causing the perception of a white color). Also, zinc oxide's radiation blocking method of protection allows it to work immediately upon application. This means that you could apply zinc oxide immediately before entering the water and, since its protection method doesn't utilize chemical processes, it theoretically doesn't lose effectiveness or require reapplication. However, recent studies have found that its effectiveness may not be indefinite, especially if applied over traditional chemical sunscreens, and that it may in fact become toxic itself.
Why Zinc Oxide Causes Issues
You may think you are being extra protective applying zinc oxide over regular sunscreen. After all, two is more protective than one, right? A study concluded in 2021 found that applying both chemical and physical sunscreens (such as zinc oxide) causes a chemical reaction which reduces the effectiveness of both. Ultimately, both become ineffective, according to the study, after two hours of sun exposure. The study also investigated zinc oxide's effects upon zebrafish (often used for testing due to their similarity to humans at the molecular level). The study found that after long exposure to UV radiation, zinc-oxide particles created nanotoxicity in the zebrafish. Since zebrafish are much smaller than humans, the toxicity resulted in pronounced effects, such as defects in fin development and size. Despite no records of humans developing shorter arms, the effects upon zebrafish suggest that zinc-oxide may be causing unknown cellular mayhem. The results could mean cancer or other cellular abnormalities.
For now, these findings are relatively new, but it's probably safest to stick to standard chemical sunscreens for UV-protection during your next beach visit. Just make sure to reapply every couple hours.
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