Where Does Sunscreen Go After a Swim? A Coconut Fungi Project Offers Clues
When you swim with sunscreen on, some of it rinses off into the water. A Hawaii high school researcher found that fungi living in coconut husks can break down both sunscreen residue and plastic in lab conditions. It is early, unpublished work, but it points to new cleanup ideas. Meanwhile, swimmers can lower what they wash off with a few simple habits.
Why sunscreen in the water gets attention
Every summer on our water programs, students ask whether their sunscreen hurts the ocean. It is a fair question. Sunscreen washes off skin while people swim, surf, and snorkel, and popular beaches can see thousands of swimmers a day.
Concern over coral reefs led Hawaii and a few other places to restrict two organic UV filters, oxybenzone and octinoxate. Scientists continue to debate how much sunscreen contributes compared with bigger threats like warming water and pollution runoff. Still, the idea of reducing chemical residue near fragile reefs has broad support, and that is where this project comes in.
The student behind the research
Vera Wang, now a Kaiser High School senior in Honolulu, did the research in Anthony Amend's UH Mānoa lab, with day-to-day guidance from marine biology grad student Kaylee Christensen. Her project won first place in the microbiology category and third place overall at Hawaiʻi's 2026 statewide science and engineering fair, along with several special awards. It also qualified her for the International Science and Engineering Fair.
It started with a filter
As a sophomore, Wang desinged an ocean filter made entirely from coconut byproducts. Its structure drew on traditional Polynesian weaving, and it removed sunscreen and microplastics from surface water. That solved one part of the problem. It raised a new question, though: once the pollutants are trapped, how do you get rid of them responsibly?
What the fungi study found
Wang learned that coconut fiber has a porous structure that lets air and water move through it, conditions that suit microbes. She wondered whether the husk could do more than physically catch pollutants. So she began studying the fungal communities that live naturally in coconut husks.
Here is what the team reported:
- Fungi from coconut husks broke down sunscreen and plastic when grown on media containing those materials.
- A tannin compound helped identify the useful fungi. Tannins already present in coconut fibers may encourage these hard-working decomposers to grow.
- Some species may be new to science. Genetic testing showed certain fungi matched nothing in the biggest global reference collection of sequenced genomes.
Keeping the findings in perspective
This is exciting work, and it deserves to be read carefully. The results come from a student research project and a university news release, not a peer-reviewed paper with detailed methods. The report does not say which sunscreen ingredients broke down, how quickly, or how completely. Lab results on growth media can look very different from what happens in a real ocean.
Even so, the idea is clever. Pairing a natural filter that traps residue with fungi that can digest it could one day lead to low-cost cleanup systems built from local farm waste. To be fair, it is the kind of early step that larger research projects often grow from.
Habits that reduce what you wash off
You do not need to wait for new technology to be a lighter presence in the water. These are the habits I teach every group before a swim or paddle:
- Cover up first. A rash guard, swim leggings, and a wide-brim hat protect large areas with no sunscreen at all.
- Apply well before you swim. Put sunscreen on at least 15 minutes before getting in so it can set on skin.
- Choose your filter thoughtfully. If local rules restrict oxybenzone or octinoxate, follow them. Many people choose zinc oxide products near reefs.
- Use lotion rather than spray on the sand. Sprays drift onto sand and water, and they are easy to under-apply.
- Reapply on schedule. Water resistance in the US is tested for 40 or 80 minutes, so reapply after swimming and toweling off.
And plan the shade. Midday breaks under a canopy cut your UV dose without adding anything to the ocean.
On the drive back from the beach, sun through side windows is easy to overlook. If that drive is in a leased car close to its turn-in date, it is worth a moment to compare your car's lease equity before deciding to return, buy, or trade it.
Frequently asked questions
Does sunscreen really end up in the ocean?
Yes. Some sunscreen rinses off skin during swimming, which is why many beach areas encourage reef-conscious products and covering up.
Can fungi clean sunscreen out of seawater now?
Not yet. The coconut husk fungi were tested in lab conditions. Real-world use would need much more research and testing.
Is mineral sunscreen better for reefs?
Many people choose zinc oxide near reefs, and some places restrict certain organic filters. The science on reef impact is still being studied.
What is the best way to protect skin while swimming?
Combine sun-protective swimwear, a water-resistant sunscreen applied before swimming, regular reapplication, and shade breaks.
Should I skip sunscreen to protect the ocean?
No. Sunburn and skin damage are real risks. Covering up with clothing lets you use less sunscreen without giving up protection.
The takeaway
This project is a small but hopeful look at how nature might help clean up after us. Until tools like this are proven, the best approach is simple: cover up with clothing, apply sunscreen thoughtfully, follow local rules, and enjoy the water.