Did you know that an average adult needs an entire palmful of chemical-based sunscreen to cover their face and body? If you’re using a spray, you should have an even sheen on your skin before you take your finger off the trigger. The vast majority of people under-apply sunscreen (and fail to re-apply at the recommended two-hour interval). Mineral-based sunscreens like zinc oxide or titanium dioxide serve as physical barriers to the sun, unlike chemical sunscreens, which means you need to be able to see it if you want it to work.
The problem with both of the above, though, is that the chemicals and micro-particles in chemical-based and mineral-based sunscreens are terrible for the ocean–and swimmers leave nearly eight million pounds of sunscreen in the oceans every year. Studies have demonstrated the damaging effects of oxybenzone, which appears in nearly all chemical sunscreens (and in particularly high concentration in spray sunscreen).
It protects your skin from UV rays, but it causes serious damage to coral reefs, including structural deformations, compromised DNA, and awakening viruses that bleach vast stretches of reef. In popular tourist destinations like the U.S. Virgin Islands and Hawaii, areas popular with tourists—who bring sunscreen into the ocean with them—have seen considerable reef die-off and up to 12 times the average concentration of oxybenzone in their waters. Hawaii is even considering a ban on sunscreens with oxybenzone to save their compromised reefs. Some of Mexico’s eco-reserves have had a similar policy in place for about a decade.
The impact of sunscreens with zinc oxide and titanium dioxide is due to the fact that they often appear as non-coated nanoparticles, which can be toxic to corals, fish, and other reef organisms. Their small size, interaction with cells, the fact that they cause oxidative stress in sunlight—meaning coral bleaching—all contribute to their toxicity. If these particles are 150 nanometers in diameter—meaning they aren’t nanoparticles—they should be safe for the oceans. Of course, mineral-based sunscreens also bear the environmental footprint of mining and refining, no matter how large the particles.