The coral reefs around the Turks & Caicos Islands are a major tourist attraction, and Mark Parrish is trying to make sure the visitors he takes there don’t kill them with cosmetics.

He co-owns Big Blue Unlimited, a tour operation that guides snorkeling, kayaking and other adventurous excursions around the islands. The company’s website states that, “Big Blue will ONLY ALLOW the use of 100 percent biodegradable sunscreen on all of our trips. Non-biodegradable sunscreen IS NOT TO BE USED on Big Blue trips.”

“We make it mandatory, which is easier said than done,” said Mr. Parrish. “The key is telling people well in advance, putting it on the website and saying this is our policy and giving them a chance to shop at home.”

After decades of learning that sunblock is vital to a healthy beach vacation, consumers may wonder what’s wrong with their Coppertone. But recent studies that link the active ingredients in protecting skin from damaging ultraviolet rays to coral bleaching has led to a global push for more reef-safe sunscreens.