Oxybenzone is the single most harmful sunscreen ingredient for coral reefs. Found in more than 3,500 skin care products worldwide, this chemical UV filter causes bleaching, DNA damage, and fatal deformities in young corals. It’s not the only problematic ingredient, though. At least ten sunscreen chemicals are now linked to marine toxicity, and several countries have started banning them.
Oxybenzone: The Worst Offender
Oxybenzone (sometimes listed as benzophenone-3 or BP-3 on labels) absorbs ultraviolet light to protect your skin from sunburn. But when it washes off into the ocean, it’s devastating to coral. A 2016 study published in the Archives of Environmental Contamination and Toxicology identified four specific ways oxybenzone damages developing coral: it increases bleaching, causes DNA damage, disrupts hormones that control skeleton growth, and produces gross deformities in baby coral.
One of the most striking findings is what oxybenzone does to coral larvae. It triggers a process where the larva becomes encased in its own skeleton, essentially turning it to bone before it can develop normally. The larvae also bleach at higher rates as oxybenzone concentrations increase, losing the symbiotic algae they depend on for energy. These effects happen at remarkably low concentrations. Research using field-relevant levels of roughly 0.06 micrograms per liter (a trace amount) found that oxybenzone accelerated coral death, especially when water temperatures were also elevated.
Oxybenzone enters the ocean two ways: directly from swimmers and snorkelers, and through wastewater systems that empty treated water near coastlines. Both routes deliver enough of the chemical to reach toxic thresholds in popular reef areas like Hawaii and the U.S. Virgin Islands.
Other Chemical Filters That Harm Reefs
Oxybenzone gets the most attention, but NOAA lists ten sunscreen chemicals that can harm marine life:
- Octinoxate: the second most commonly banned ingredient, often paired with oxybenzone in legislation
- Octocrylene: another chemical UV absorber found in many mainstream sunscreens
- Benzophenone-1 and Benzophenone-8: related compounds in the same chemical family as oxybenzone
- OD-PABA: an older UV filter still present in some products
- 4-Methylbenzylidene camphor and 3-Benzylidene camphor: chemical filters more common in European formulations
- Nano-titanium dioxide and nano-zinc oxide: mineral filters ground to extremely small particle sizes
A related compound called benzophenone-2 (BP-2), used in soaps, cosmetics, and body fragrances since the 1960s, is also highly toxic. NOAA researchers found that even very low concentrations of BP-2 can quickly kill juvenile corals, cause bleaching, and damage coral DNA in ways that increase mutation rates.
The Damage Goes Beyond Coral
Reef fish are also affected. Oxybenzone acts as an endocrine disruptor in fish, mimicking estrogen and interfering with reproductive hormones. In studies on Japanese medaka, exposure to oxybenzone reduced egg production, lowered hatching rates, decreased testosterone levels, and disrupted the genes responsible for producing sex hormones. These effects carried into the next generation: the offspring of exposed fish showed altered growth patterns even when they weren’t directly exposed themselves.
This matters because coral reefs are ecosystems, not just collections of coral. When both the reef structure and the fish that depend on it are harmed by the same chemical, the cascading effects multiply.
Why Mineral Sunscreens Are Safer (With a Caveat)
Mineral sunscreens use zinc oxide or titanium dioxide to physically block UV rays instead of absorbing them with chemicals. They’re generally considered a better option for reef areas because they cause fewer effects on aquatic organisms. But particle size matters. When these minerals are ground down to nanoparticles (typically under 100 nanometers) to make the sunscreen feel less chalky on skin, they appear on NOAA’s list of chemicals that can harm marine life.
If you’re choosing a reef-safer sunscreen, look for “non-nano” zinc oxide or titanium dioxide. These larger particles sit on the skin’s surface and are less likely to be absorbed by marine organisms. No sunscreen is completely without environmental impact, but non-nano mineral formulas are the closest option currently available.
Where These Ingredients Are Banned
Palau became the first country to ban reef-toxic sunscreen, prohibiting the sale or use of products containing any of ten harmful ingredients. Hawaii passed a similar law banning oxybenzone and octinoxate, which took effect in 2021. The U.S. Virgin Islands and the Dutch Caribbean island of Bonaire have enacted their own bans as well.
These laws vary in scope. Some ban only oxybenzone and octinoxate, while Palau’s covers a broader list of ten chemicals. If you’re traveling to a reef destination, check local regulations before packing sunscreen. Many major brands now sell formulations labeled “reef-safe” or “reef-friendly,” though these terms aren’t regulated by the FDA, so reading the ingredient list yourself is more reliable than trusting marketing claims.
How to Read a Sunscreen Label
The active ingredients are listed at the top of any sunscreen label, usually in their own section. To avoid the most harmful chemicals, skip any product listing oxybenzone, octinoxate, or octocrylene as active ingredients. Look instead for zinc oxide or titanium dioxide, ideally with “non-nano” specified somewhere on the packaging.
Beyond the active ingredients, check for benzophenone compounds in the inactive ingredient list, where they sometimes appear as fragrance stabilizers rather than UV filters. A product can be free of chemical sunscreens but still contain reef-toxic additives in its base formula. The simplest approach: the shorter and more recognizable the ingredient list, the less likely it is to contain something problematic for marine life.