When city leaders in the Florida resort town of Key West voted earlier this year to ban the sale of sunscreens that scientists say are harmful to coral reefs, it was, in the words of mayor Teri Johnston, “a black and white issue”.

Fearful of accelerating the decline of the fragile Great Florida reef – the 360-mile band of living coral stretching from west of the Florida Keys to the state’s Atlantic coast – commissioners believed they were taking an important step for environmental preservation.

Florida’s Republican politicians, however, are framing the issue as a matter of public health as they pursue legislation at the state level seeking to overturn the ban, using the same arguments that failed to stop Hawaii enacting a similar measure in 2018. In effect, the debate has become one of protecting coral reefs versus preventing skin cancer.

Backed by dermatologists who cite Florida’s soaring rates of melanoma, the deadliest form of skin cancer, they say it would be dangerous to ban the sale of sunscreens containing the chemicals oxybenzone and octinoxate, which filter ultraviolet rays.

“Unfortunately, with all the wonderful things that come with our beaches and sunshine, we also rank second in the nation for the highest rate of new melanoma cases,” state senator Rob Bradley, sponsor of the bill, told the senate’s industry committee.

He said the Key West ban, set to take effect in January 2021, would remove many of the leading brands of sunscreen from the shelves, including products by Hawaiian Tropic, Banana Boat and Coppertone that use the chemicals, and eliminate the public’s “first line of defense” against skin cancer.

Bradley’s bill gathered momentum in Tallahassee this week, setting up a likely battle in the senate early next year that will pit the expert testimony of doctors against that of environmentalists.

Johnston, meanwhile, said Bradley was wrong to portray the ordinance as downplaying the importance of sunscreen and pointed out that there were many sunscreen brands – often made by smaller firms – that could still be used. “You should use sunscreen [but] we would like you to use a safe sunscreen for our coral reef when you’re in the Keys,” she said. “There are literally hundreds of alternative sunscreens that do not include these two ingredients.

“We have enough scientific information that says they are harmful to our last remaining coral reef and it’s incumbent on us to do everything we can to protect it. The reef is the centre of our economy and tourist trade and a source of enjoyment for all of Florida and the world.”

Awareness of the impact of chemicals on coral reefs appears to have grown since Hawaii’s 2018 decision. Coppertone, a leading sunscreen manufacturer, said its scientists were working on new formulas without oxybenzone or octinoxate, and in August the pharmacy chain CVS announced it would remove the chemicals from store-branded varieties of its sunscreens by the end of 2020.

The chemicals oxybenzone and octinoxate, which are found in some sunscreens, help protect from skin cancer but are harmful to coral reefs. Photograph: PhotoAlto/Frederic Cirou/Getty Images

Additionally, the federal food and drug administration (FDA) issued proposed changes to sunscreen regulations in February, with a final ruling imminent, and sought information from manufacturers about the safety and effectiveness of 12 active sunscreen ingredients. The National Oceanic and Atmospheric Administration, meanwhile, published information based on scientific studies blaming chemicals in sunscreens for harm to marine life and coral reefs.

“Studies have shown that just a tiny drop of sunscreen can kill coral five to 20 miles offshore,” said Justin Willig, conservation travel programs coordinator of the Oceanic Society, which recommends alternative “reef-safe” sunscreens containing zinc oxide or titanium oxide.

“It causes coral bleaching at lower temperatures, can damage the DNA which leaves the coral unable to reproduce, and some of the chemicals can become endocrine disruptors which leads to abnormal skeleton growth and eventually causes the junior corals to die.”

However, some dermatologists in Florida remain skeptical of the science used to promote sunscreen bans and question claims that there are suitable alternative products.

“I was born and raised in south Florida and have seen the skin cancer epidemic blossom to the point where one person dies every hour of melanoma in the US and another person dies of squamous cell carcinoma,” said Dr Andrew Weinstein, immediate past-president of the Florida society of dermatology and dermatological surgery.

“There’s excellent data that shows that people who use sunscreen get fewer cutaneous tumors and also data that shows people will avoid using sunscreens they don’t like. Mineral sunscreens feel chalky and sticky, and people will use less.

“Key West acted extremely irresponsibly. It will lead to increased cancer risks anywhere where sunscreen is not available.”

Deborah Foote, director of government affairs for the Sierra Club of Florida, sees evidence of a power grab in state politicians’ efforts to reverse the ban.

“The bigger picture is the continuing pre-emption of local jurisdictions from being able to regulate issues that are important and unique to their community,” she said. “Particularly with the environment there are aspects in Florida more appropriate to local decision-making.

“Everyone should take a deep breath and wait for the FDA outcome which is supposedly at the end of this month. If these chemicals are removed from the approved list they’re going to be going away anyway.”