Most sunscreens harm corals. Here's what you can do

Every time you go for a swim, some of your sunscreen gets left behind.

An estimated 25% of applied sunscreen washes off during recreational water activities, releasing some 5,000 tons annually in reef areas alone, according to a study in Environmental Health Perspectives. That’s equivalent to the weight of about 1,000 elephants, and many of those chemicals are toxic to corals. Some researchers argue that may be a low estimate, noting the experiment did not replicate the friction caused by swimming, which could cause more sunscreen to rub off.

Coral reefs support about a quarter of all marine species despite covering just 0.1% of Earth's oceans. Already under mounting pressure from warming waters, pollution, overfishing and coastal development, reefs face an additional threat from sunscreen chemicals that can damage coral larvae, trigger bleaching and disrupt growth. Scientists say it’s a smaller stressor than climate change, but one consumers can actually address.

The pollution doesn’t just come from swimming. Sunscreen chemicals can enter waterways when people shower, wash towels or urinate after beach trips. Sewage is the largest source of sunscreen contamination in oceans, as conventional treatment plants can’t effectively remove many UV filter compounds, studies show. The chemicals flow from wastewater facilities into rivers and ultimately the sea.

While sunscreen prevents sunburn and reduces skin cancer risk, not all formulas carry the same environmental footprint.

The strongest evidence of harm centers on oxybenzone and octinoxate — two widely used chemical UV filters. A 2016 study published in Archives of Environmental Contamination and Toxicology found oxybenzone transforms coral larvae from healthy, mobile organisms into deformed, immobile ones. The chemical causes corals to expel the algae that provide much of their food and color, a stress response known as bleaching. Bleached corals are weakened, more vulnerable to disease and can starve or die if stressful conditions persist. Researchers also found oxybenzone damages DNA and triggers premature skeleton formation that can encase entire larvae. It can also cause corals to bleach at lower temperatures, worsening the effects of marine heat waves driven by climate change.

The chemical proves toxic at concentrations as low as 62 parts per trillion — equivalent to one drop in six Olympic-sized swimming pools. At Hanauma Bay, a popular Hawaii snorkeling spot, nearly 2,600 daily visitors left around 412 pounds of sunscreen in the ocean each day, according to a 2017 study by nonprofit Haereticus Environmental Laboratory.

Scientists have growing concerns about octocrylene, avobenzone and homosalate as well.

These chemicals don’t stay put. UV filters have been detected in fish and other marine organisms, raising questions about seafood safety.

“We measured the level of oxybenzone in locally caught fish. It was scary,” said Craig Downs, executive director of nonprofit Haereticus Environmental Laboratory, who led the 2016 study. “These chemicals move through the food chain, then we eat it.”

Zinc oxide and titanium dioxide are generally considered safer alternatives to chemical UV filters, but they come with caveats. Experts say they should be in non-nano form, as their larger particle size makes them less likely to be inhaled or absorbed by marine organisms.

Zinc oxide can also contain trace heavy metal impurities such as lead, chromium and mercury, Downs said, and few products have undergone comprehensive ecotoxicity testing.

Consumers should also pay attention to inactive ingredients, since oils, fragrances and other additives can harm marine life.

Some mineral sunscreen manufacturers add UV filters such as butyloctyl salicylic acid and ethylhexyl methoxycrylene to prevent SPF levels from degrading in zinc oxide, which Downs has linked to potential cancer risks and coral toxicity.

Experts recommend covering up with clothing, rash guards, hats and shade.

“If you put on a rash guard or long sleeve swim shirt, you basically cover up 50% of your body, which means you don’t need 50% of the sunscreen,” Downs said. “From a conservation perspective, that’s a massive win.”

When sunscreen is needed, look for products with non-nano zinc oxide or titanium dioxide as active ingredients. While research continues into how these minerals behave in marine environments, many experts consider them preferable to chemical UV filters.

Though mineral sunscreens have a reputation for leaving a white cast, newer formulations offer sheerer alternatives.

Experts also recommend avoiding aerosol sprays, which can disperse sunscreen into the air and surrounding environment. Waiting at least 15 minutes after applying sunscreen before swimming allows it to better adhere to skin rather than wash off immediately.

In 2018, Hawaii became the first U.S. state to prohibit the sale of sunscreens containing oxybenzone and octinoxate, citing their harm to coral reefs. Key West, Florida, has followed with a similar measure. Palau and the U.S. Virgin Islands have gone further, restricting a broader list of chemicals linked to reef damage.

Beyond those bans, the marketplace remains largely unregulated. Labels like “reef safe” or “reef friendly” have no universal definition or standard.

“People can just write whatever they want on a bottle, and there’s no validation, no testing, no standardization,” said Michael Sweet, head of the Nature-based Solutions Research Centre and the Aquatic Research Facility at the University of Derby in England.

In lab experiments, some formulations “have decimated corals before my very eyes,” he said. “When you see that, you wonder what’s being put into our oceans on a daily basis, from shampoos, skin care, conditioners and shower gels. All this stuff goes into our rivers and ultimately our oceans.”

Some independent certifications have emerged to help consumers make informed decisions. One example is Protect Land + Sea, a label created by Downs’ laboratory that verifies products are free of ingredients such as oxybenzone, octinoxate and parabens. Experts note that ingredient screening can be useful, though it is not the same as comprehensive ecological safety testing of an entire formula.

“Reefs are being hammered left, right and center,” Sweet said. “Every little bit we can do tips the balance a little bit further up and hopefully gives them that bit of a fighting chance.”

Follow Annika Hammerschlag on Instagram: @ahammergram.

The Associated Press receives support from the Walton Family Foundation for coverage of water and environmental policy. The AP is solely responsible for all content. For all of AP’s environmental coverage, visit https://apnews.com/hub/climate-and-environment

FILE - A man takes a shower near a beach during a hot day in Palaio Faliro suburb, south of Athens, Greece, July 6, 2025. (AP Photo/Yorgos Karahalis, File)

FILE - A woman applies sunscreen to a man at Avlaki beach east of Athens, Greece, Aug. 7, 2025. (AP Photo/Thanassis Stavrakis, File)

FILE - A resort worker folds up beach umbrellas Aug. 16, 2025, in South Yarmouth, Mass. (AP Photo/David Goldman, File)

FILE - Bleached coral is visible at the Flower Garden Banks National Marine Sanctuary, off the coast of Galveston, Texas, in the Gulf of Mexico, Sept. 16, 2023. (AP Photo/LM Otero, File)

Every morning before opening, Ocean Park staff tend to the coral display near the entrance of the Grand Aquarium – brushing algae off coral fragments, moving them to better positions and feeding them with care.

Expert care: The Chinese University of Hong Kong collects coral fragments in Hong Kong waters and hands them over to Ocean Park for restoration. Image source: www.news.gov.hk

These corals were formerly in the sea, where they faced threats such as bleaching, caused by higher ocean temperatures, and human activity. At Ocean Park they are being rehabilitated, and also serve as a living teaching aid for marine conservation.

The tanks are fitted with lighting and filtration systems specially designed for corals, and fish can be seen swimming inside. Accompanied by educational panels and videos, they draw visitors to linger and watch. From Wednesday to Friday at designated times, interactive guided sessions are provided on coral care, biodiversity and restoration work.

Coral conservation

Awarded a grant of more than $3.5 million from the Environment & Conservation Fund (ECF), Ocean Park launched the exhibition earlier this year. Showcasing 12 species of hard and soft corals found in Hong Kong waters, it has attracted more than a million visitors to date.

The funding also covered renovations to other facilities at the aquarium and the establishment of the Coral Ecology & Conservation Discovery Centre, now a key venue for coral rehabilitation and public education.

“This project combines coral conservation, public awareness and education,” said Ocean Park Lead Conservation Manager Ashley Kwok.

Immersive experience: Jarvis Ng (left) and Jit So take part in a workshop to learn about different coral species and how cultivation tanks work. Image source: www.news.gov.hk

Ms Kwok explained that the park works closely with Chinese University of Hong Kong (CUHK) School of Life Sciences Assistant Professor Apple Chui and the Coral Academy founded by her. CUHK provides coral fragments collected in Hong Kong waters and professional advice on local coral cultivation, while Ocean Park provides the facilities to ensure quality care.

Immersive learning

The discovery centre, located in the back-of-house area of the Grand Aquarium, is equipped with professional coral care facilities and runs STEAM (science, technology, engineering, arts and mathematics) workshops and public guided tours.

On a recent visit, a group of primary school pupils took part in an on-site workshop, gaining an immersive introduction to coral restoration and other aspects of marine conservation.

“Are corals animals?” a coral care worker asked. The children eagerly raised their hands to answer “yes”, as they touched coral specimens under guidance and learned about what is needed to set up a cultivation tank.

Coral revival: Ocean Park Lead Conservation Manager Ashley Kwok says cultivated, restored coral fragments will be transplanted back to Hong Kong waters to rebuild coral communities and enrich local marine ecology. Image source: www.news.gov.hk

Jit So, who is in Primary Six, drew a picture with his classmates showing how different coral species are placed in various positions in a tank according to their habits and requirements, which involve aspects such as shading needs and water flow strength, so that they can grow well.

Jarvis Ng, from Primary Four, said he had seen corals while snorkelling before but had not known previously that coral polyps live inside corals and feed on plankton. He also put on virtual reality glasses to glimpse a coral habitat, saying it really felt like being underwater.

Ocean Park says the workshops, launched just a month ago, have already engaged more than 100 pupils, while the guided visits have involved over 1,600 participants.

The park also plans to run a teacher training programme in the first half of next year so that primary school teachers can bring conservation knowledge back to the classroom.

Coral fragments that have been cultivated and restored to health will be transplanted back to southern Hong Kong waters to rebuild coral communities and enrich the marine ecology of restoration sites.

Proud record: Environment & Conservation Fund Committee Chairman Eric Cheng says the fund has supported more than 7,200 environmental projects and activities since its establishment. Image source: www.news.gov.hk

Green transition

ECF Committee Chairman Eric Cheng said the coral project showcases innovative local restoration techniques, promotes environmental awareness and encourages people to take action to protect the environment.

“When corals can live healthily, it also indirectly proves that Hong Kong has excellent water quality and that the natural environment is well protected,” he remarked.

Mr Cheng outlined that the ECF has funded more than 7,200 environmental projects and activities over its 32-year history, disbursing a total of over $4.7 billion in funding. He added that many of the projects are closely related to people’s daily lives, covering areas such as waste reduction at source, recycling, biodiversity, carbon neutrality, low-carbon living, clean shorelines and clean air.

Citing food waste pre-treatment system projects as an example, he said the ECF had approved about $73 million as of September to fund about 25 premises, including private housing estates and universities, in adopting the locally developed “Food TranSmarter” system.

The technology converts food waste into slurry, which is then sealed and sent to government central treatment facilities, reducing door-to-door collections to once or twice a week and significantly lowering carbon emissions and total costs. The projects also encourage different sectors to actively participate in food waste recycling.

Discovering corals: Ocean Park’s coral exhibition, backed by the Environment and Conservation Fund, has attracted over one million visitors to date. Image source: www.news.gov.hk

Mr Cheng remarked that in future the ECF will steer its approvals towards local and national green transition initiatives, in particular the Hong Kong Climate Action Plan 2050 and the development of the Northern Metropolis. He said the ECF fully supports the Government’s policy direction and welcomes applications from eligible local organisations for funding related to environmental protection and nature conservation.