The best way to avoid damage from the sun is to stay in the shade from 10 a.m. to 2 p.m., when the sun’s rays are the strongest, and wear long sleeves and hats. But for Emily Silva, that’s not an option.

Silva teaches swimming, snorkeling and kayaking in Maui so she’s outside all day every day. While an effective sunscreen is vital to her health, her livelihood depends on the health of reefs around Maui.

The environmental impact of sunscreen is a concern other readers had as well, and in the second episode of our podcast “Are We Doomed? And Other Burning Environmental Questions” we dive into the complicated reasons why sunscreen can be dangerous for coral and other marine life.

Three indicators that a sunscreen is eco-friendly 1. Mineral-based: The active ingredient should be zinc oxide or titanium dioxide. Avoid sunscreen that has oxybenzone, avobenzone, octisalate, octocrylene, homosalate or octinoxate. 2. Non-nano: This means the particles are large enough that they won’t be absorbed by the coral. 3. Pharmaceutical-grade: This means the zinc oxide and titanium dioxide are as pure as possible, so they’re free of harmful heavy metals like lead, nickel, cobalt and aluminum.

Stuart Coleman, Hawaii manager of the Surfrider Foundation, said there are three main things you should look for in your sunscreen’s ingredient list: mineral-based, non-nano particles and pharmaceutical-grade.

“If you see something that’s really cheap and in a big plastic container, it’s got tons of chemicals that you can’t pronounce, you know that that’s probably going to be bad for you and the environment,” Coleman said.

But the idea of a 100% reef-safe sunscreen is a misnomer, said Craig Downs, a researcher with Haereticus Environmental Laboratory. That’s because every ingredient in sunscreen is foreign to marine ecosystems and can have a negative impact when introduced in large quantities.

“There’s a reason it’s called sunscreen pollution,” he said.

Investing in swimwear with built-in sun protection and long-sleeves, like wetsuits, helps reduce the impact on the marine environment because you’re putting less sunscreen on.

Courtesy of Kiera Ryon and Kiana Liu

“Whatever you have on your skin is going to come off your skin and get in the water,” he said. Which is why it’s important for consumers to read the ingredients in their sunscreens and not rely on packaging that says “reef-safe” or “reef-friendly.”

“It’s a form of green-washing,” said 18-year-old Taylor Redman. “Which is a marketing ploy that businesses use saying that their product is eco-friendly but they actually aren’t.”

Redman and fellow classmate Kiana Liu formed a group called “The Sunscreen Police of Maui” in their senior year of high school. They set up tables near popular beaches around the island with information about how certain chemicals have been connected to coral bleaching.

Redman said locals and tourists alike stopped for help analyzing their sunscreen, and many were surprised to learn that sunscreens advertised as “reef-safe” can still contain chemicals that hurt reefs.

Courtesy of Kiera Ryon and Kiana Liu

“There’s more chemicals than just oxybenzone and octinoxate that are bad,” Liu said. “But if a sunscreen doesn’t have those two they say it’s safe when it’s not.”

The duo also handed out samples of mineral-based sunscreen, but not everyone wanted to give up the convenience of spray-on protection. The students saw some people who took a sample use harmful sunscreen later in the day.

“That was kind of discouraging because you know the sunscreen isn’t cheap and we got some of it donated from local companies that are on Maui,” Liu said.

But Liu and Redman said most people were interested and wanted to change their behavior.

Arielle Levine is a professor of geography at San Diego State University and worked with NOAA’s Coral Reef Conservation Program. Last year her team visited beaches across Hawaii and asked beach-goers if they were aware of the upcoming ban on oxybenzone and octinoxate in sunscreens.

“The majority of people we talked to really do want to do the right thing,” Levine said. “I think that’s something that was really encouraging from the survey.”

Seventy-five percent of people surveyed by Levine and her team said they were aware that certain chemicals in sunscreen could hurt marine ecosystems, and even a majority of international visitors knew about the risks.

“I was surprised how many people were actually aware of the issue,” she said. “I thought it was kind of a niche topic.”

Hawaii residents were by far the most informed, with 92% of people from the state saying they were aware of the harmful effects of oxybenzone and octinoxate. However, 20% of Hawaii residents were still using a sunscreen with those ingredients. Visitors were more likely to be using a sunscreen with oxybenzone or octinoxate — 32% of visitors from other U.S. states and 23% of international visitors.

Levine said she spoke with many tourists who thought the oxybenzone and octinoxate ban was already in effect, and waited to purchase their sunscreen in Hawaii for that reason.

“They were trying to do the right thing,” she said.

Climate change is a much bigger threat to reefs, since higher ocean temperatures lead to coral bleaching. Fertilizer and sediment runoff also introduce harmful substances into marine environments and can impair the coral’s growth.

But Levine thinks the topic of reef-friendly sunscreen is so well known because it makes people feel less helpless.

“What sunscreen you choose to apply is something you have complete control over,” she said.