How Oxybenzone in Sunscreen Bleaches Coral Reefs

Oxybenzone is the most widely used UV filter in commercial sunscreens. It absorbs UVA and UVB radiation effectively, spreads easily on skin, and costs almost nothing to manufacture. It is also one of the most destructive chemicals entering the ocean through recreational swimming.

What Oxybenzone Does to Coral

Coral bleaching happens when coral expels the symbiotic algae (zooxanthellae) living in its tissue. These algae provide coral with up to 90% of its energy through photosynthesis. Without them, coral turns white, starves, and often dies.

Oxybenzone triggers this process through multiple pathways.

The compound converts sunlight into a form of oxidative stress that damages coral DNA. Healthy coral can repair DNA damage to a point. Oxybenzone overwhelms that repair capacity. A 2016 study published in Archives of Environmental Contamination and Toxicology found measurable DNA damage in coral exposed to oxybenzone at concentrations of just 62 parts per trillion. For scale, that is roughly equivalent to one drop of oxybenzone in 6.5 Olympic swimming pools of water.

Oxybenzone also disrupts coral reproduction. It acts as an endocrine disruptor, interfering with the hormones that regulate coral spawning cycles. Exposed coral produces fewer viable larvae, and the larvae it does produce are deformed.

The most disturbing effect: oxybenzone causes coral larvae to encase themselves prematurely in their own calcium carbonate skeletons. The larvae effectively entomb themselves. They cannot swim, cannot settle on new substrate, cannot grow into adult coral. They die encased in their own armor.

How It Gets Into the Water

An estimated 14,000 tons of sunscreen enter the ocean annually. A single swimmer wearing conventional sunscreen releases 4-6 milligrams of oxybenzone per swim. In popular snorkeling and beach destinations, water concentrations regularly exceed the 62-parts-per-trillion threshold by orders of magnitude.

Researchers in the U.S. Virgin Islands measured oxybenzone concentrations at popular snorkeling sites at 1,400 parts per trillion. Hawaii’s Hanauma Bay, visited by over a million snorkelers per year, has recorded levels above 19,000 parts per trillion. These numbers are 20 to 300 times the level that causes measurable harm.

But swimming is not the only pathway. Wastewater treatment plants do not fully remove oxybenzone. When you shower after applying sunscreen, it enters the sewage system and eventually reaches coastal waters. Studies in the Mediterranean have detected oxybenzone in seawater at sites with no nearby recreational swimming, traced entirely to wastewater discharge.

The Research Timeline

The concern is not new. In 2008, a team led by Roberto Danovaro at the Polytechnic University of Marche in Italy published the first major study linking sunscreen chemicals to coral bleaching. They tested several UV filters and found that oxybenzone, along with butylparaben, ethylhexyl methoxycinnamate (octinoxate), and 4-methylbenzylidene camphor, all caused rapid and complete bleaching of hard coral within 96 hours.

In 2015, Craig Downs and colleagues at the Haereticus Environmental Laboratory published the landmark study quantifying the toxicity threshold at 62 parts per trillion. This study was instrumental in subsequent legislation.

By 2018, Hawaii became the first US state to ban the sale of sunscreens containing oxybenzone and octinoxate. The law took effect in 2021. Palau, the US Virgin Islands, Key West (Florida), and several Caribbean islands followed with their own bans.

It Is Not Just Coral

Oxybenzone affects other marine organisms too. Green algae show reduced growth rates at environmental concentrations. Sea urchin embryos develop abnormally. Dolphin tissue samples from coastal populations contain detectable oxybenzone levels. Fish exposed to the compound in laboratory settings show signs of feminization and altered reproductive behavior.

The compound bioaccumulates. It persists in marine sediment and builds up in the food chain. Even when surface water concentrations drop seasonally (fewer swimmers in winter), the sediment reservoir continues to release oxybenzone into the water column.

What You Can Do

Switch to mineral sunscreen that uses zinc oxide or titanium dioxide as the active UV filter. These minerals sit on the skin’s surface and do not dissolve into seawater the way oxybenzone does.

Check your current sunscreen’s active ingredients. If you see “oxybenzone,” “benzophenone-3,” or “BP-3,” it contains the compound. Replace it.

If you are visiting coral reef areas, the switch is not optional. It is the minimum responsible action. A single tube of reef-safe sunscreen costs the same as a conventional one. The coral reef it helps protect took centuries to grow.

Read our full reef-safe sunscreen guide for specific ingredient recommendations and label-reading instructions. And check out our coverage of Hawaii’s sunscreen ban for more on the legislation driving this change.