Avobenzone is not considered reef safe. While it appears less immediately toxic to corals than oxybenzone, the most studied reef-harmful UV filter, avobenzone accumulates in coral tissue, breaks down into compounds that may be far more toxic than the original chemical, and is outright banned in at least one country specifically for reef protection. The full picture is more nuanced than a simple yes or no, but if you’re shopping for a reef-friendly sunscreen, avobenzone is one to avoid.
What Avobenzone Does to Coral
Avobenzone on its own doesn’t appear to cause immediate, dramatic coral damage at low concentrations. In lab studies, it didn’t trigger coral inflammation at 1 mg/L. But the real concern is what happens after coral absorbs it. Over a seven-day exposure period, corals accumulated modified forms of avobenzone at levels 1.3 to 32 times higher than the original compound. These modified forms, called dihydroBM esters, are predicted to be between 1,000 and 900,000 times more toxic to aquatic organisms than avobenzone itself.
There are also signs that avobenzone interferes with coral’s ability to photosynthesize. At concentrations of 300 micrograms per liter, two key carotenoid pigments in coral decreased significantly. Carotenoids are essential for the tiny algae living inside coral tissue (the organisms that give coral its color and provide it with energy). A drop in these pigments suggests avobenzone could contribute to bleaching, the process where corals expel their algae and slowly starve. Researchers noted that 13 coral metabolites shifted significantly after just seven days of exposure, with effects beginning at that 300 microgram threshold.
How It Compares to Oxybenzone
Oxybenzone is the UV filter with the worst reputation for reef damage, and for good reason. It disrupts coral photosynthesis at concentrations as low as 0.06 micrograms per liter, a tiny fraction of what’s needed for avobenzone to show effects. That makes oxybenzone roughly thousands of times more potent as a direct coral toxin. Hawaii’s landmark 2018 sunscreen ban targeted oxybenzone and octinoxate specifically, not avobenzone, largely because the evidence against those two was stronger at the time.
But “less harmful than oxybenzone” is a low bar. Avobenzone’s danger is subtler: it builds up in coral tissue and transforms into compounds whose toxicity may rival or exceed oxybenzone’s. The science on these breakdown products is still catching up to the science on oxybenzone, which has been studied more extensively. That gap in research is part of why avobenzone has escaped some of the bans that caught oxybenzone, not because it’s been proven safe.
Breakdown Products in Water
Avobenzone is notoriously unstable when exposed to UV light, which is ironic for a sunscreen ingredient. In water, it undergoes several transformations: it can change shape (photo-isomerization), degrade into smaller molecules, and react with chlorine or bromine in the water. Researchers have identified over 60 transformation products when avobenzone interacts with chlorine and bromine, including chlorinated phenols and acetophenones, both of which are known to be toxic to aquatic life.
In seawater specifically, bromination of avobenzone produced 33 distinct byproducts. The toxicity of most of these compounds hasn’t been individually tested, which is part of the problem. You’re not just introducing avobenzone into the ocean when you swim. You’re introducing a chemical that rapidly breaks apart into dozens of other compounds, many of them potentially more harmful than what you started with.
Effects on Fish and Other Marine Life
Coral isn’t the only concern. Zebrafish studies have shown that avobenzone accumulates in fish tissue and doesn’t clear out, even after 72 hours in clean water. That persistence matters because it means avobenzone can build up in marine food chains over time.
In developing zebrafish, avobenzone exposure affected genes involved in nervous system development, disrupted antioxidant enzyme activity, and inhibited locomotor behavior. When combined with nanoplastics (tiny plastic particles already widespread in ocean water), avobenzone accumulation in fish tissue increased further. The antioxidant system couldn’t fully recover even after the exposure ended, suggesting lasting biological effects rather than temporary stress.
Where Avobenzone Is Banned
Palau, the Pacific island nation known for aggressive marine conservation, banned avobenzone outright as part of its 2020 sunscreen regulations. The law prohibits anyone from bringing sunscreen containing avobenzone into the country, and bans its import, manufacture, sale, and distribution. Palau went further than most jurisdictions by banning not just avobenzone itself but all dibenzoyl derivatives, the broader chemical family it belongs to.
Hawaii’s ban, which took effect in 2021, targeted only oxybenzone and octinoxate. Several other regions and marine parks have similar narrow bans. Palau’s approach of casting a wider net reflects growing awareness that the problem extends beyond just the two most-studied chemicals.
Certification and Safety Lists
The Haereticus Environmental Laboratory, which developed the “Protect Land + Sea” certification you’ll see on some reef-safe sunscreen labels, does not include avobenzone on its HEL List of banned chemicals. Their list targets oxybenzone, octinoxate, octocrylene, homosalate, octisalate, and several parabens, among others. So a sunscreen containing avobenzone could technically carry a “reef safe” certification from this program.
This is worth knowing because it means “reef safe” labels don’t guarantee the absence of avobenzone. If avoiding avobenzone matters to you, check the active ingredients list rather than relying on front-of-package claims.
Separately, the FDA classified avobenzone as “non-GRASE” (not generally recognized as safe and effective) in its 2019 review, meaning the agency determined there isn’t enough safety data to confirm it’s safe for human use either. This classification applies to human health rather than environmental impact, but it reflects broader uncertainty about the chemical’s safety profile.
What to Use Instead
Mineral sunscreens using non-nano zinc oxide or non-nano titanium dioxide are the most widely accepted reef-safer alternatives. “Non-nano” means the particles are large enough that they’re less likely to be absorbed by marine organisms. Nano-sized versions of these minerals are on some environmental concern lists, including the HEL List, so the particle size matters.
If you’re traveling to Palau or other destinations with strict sunscreen laws, mineral-only formulas are your safest bet for compliance. For everyday use near reefs or in ocean water, switching away from avobenzone (along with oxybenzone and octinoxate) reduces the chemical load you’re adding to the water, even if no single swimmer’s sunscreen will make or break a reef ecosystem. The concern is cumulative: thousands of swimmers at popular reef sites, day after day, adding up to concentrations that start to matter.