If you walk along South Beach right now, you might notice something strange, even by Florida standards: Dotting the sandscapes are sky-blue boxes that supply free sunscreen. In a novel experiment this year, Mount Sinai Medical Center partnered with the City of Miami Beach to put 50 dispensers in public spaces, and those dispensers are full of radiation-mitigating goo, free to any and all passersby. The sunscreen even comes with local celebrity endorsements: “I have a bottle of Miami Beach SPF 30 on my desk,” Mayor Philip Levine told Forbes. “It’s a great product. I’ve used it.”

And it’s the kind of sunscreen that’s actually supposed to be effective at preventing cancer and premature aging (of the skin): Broad-spectrum, water resistant, and SPF 30. Those are the three characteristics that the American Academy of Dermatology now recommends in a sunscreen. But most people don’t know that, and end up wasting money, confidence, and skin. When it comes to sunscreen, people are getting burned—by ignorance. Also, by the sun.

Barraged by untold drugstore products and cosmetic industry marketing, confusion ends up costing not just money but lives, according to Roopal Kundu, an associate professor of dermatology at Northwestern University. This week she and colleagues shed some light (not too much) on just how misunderstood sunscreen is. After polling patients at their Chicago clinic, the dermatologists reported that only 43 percent knew what SPF ratings actually mean. Preventable skin cancer kills thousands every year, but the number-one reason people said they use sunscreen was not because they care about cancer, but because they care about burns. And only 7 percent knew what to look for on a label if they want a product that is actually proven—among the many products making similar claims—to protect against premature aging (of the skin).

City of Miami Beach

For example, the sunscreen being dispensed in Miami is labeled as “Infused With Triple Acting Sea Kelp.” I reached out to the manufacturer for some clarification on what the hell that means, and they sent a press statement: “The sea kelp offers unique benefits of helping to restore proteins and minerals lost in the sun, firming the appearance of the skin and helping to protect against photo-aging with its natural sunscreen properties.” Living kelp does release iodides to protect itself from exposure at low tide, and phlorotannins to help absorb UV-B. But I find no evidence to support the assertion that kelp is an effective ingredient in human sunscreen. I've also never seen a sunburned sea kelp! Snare drum. Anyway, I think it’s important to have fun with science.

You can buy a product that is labeled as higher than SPF 30, but it’s almost always a waste, and potentially harmful. SPF 15 filters out about 93 percent of UV-B rays. SPF 30 filters out approximately 97 percent. SPF 50 filters out approximately 98 percent. SPF 100 might get you to 99. The problem, though, is the psychology of the larger number. Above 30, the difference is essentially meaningless, and higher SPFs do not last longer than lower SPFs — but they do tend to make people feel invincible. We put on the "more powerful" sunscreens and then suddenly think we're Batman or some other superhero who can stay out in the sun indefinitely. But no sunscreen is meant to facilitate prolonged exposure of bare skin to direct sunlight.

A recent report by the Environmental Working Group notes that several years ago the FDA deemed SPF labels above 50 to be “inherently misleading” but has not prohibited the practice, even while European and Japanese regulators do not allow products to be labeled above 50, and in Canada the maximum labeling possibility is 50+.

That’s not even accounting for the fact that SPF is an outdated term, in that it only refers to protection from UV-B rays, not UV-A, which don't cause sunburns but are no less dangerous in terms of skin cancer. I bet if the inventor of SPF, Austrian mountaineer and photobiologist Franz Greiter were alive today, he would say “I don’t regret what I did, because it made sense at the time. Heck, I invented wearable sunscreen. Give me some credit. But, I will say, knowing what we know now, there is clearly a more effective way to communicate information than the SPF system. We could use a more comprehensive, intuitive metric.”

UV-A coverage not only protects against DNA damage and cancer, but also protects against premature skin aging. The only way that UV-A coverage is communicated on a label is with the words broad spectrum. Unless a sunscreen says that, it’s almost sunscreen in name only. And there is no metric for just how much UV-A coverage is provided by a broad-spectrum product. The Northwestern dermatologists tested out a five-star rating system for UV-A coverage, and their patients took to it well. But given that the SPF system has been around for decades and most people still don’t understand it, there’s clearly benefit in keeping things simple.

"There's only so much sunscreen information that people can process," Kundu said when we spoke this week. “I emphasize broad-spectrum, SPF 30, and water resistance. And that, like any tool, you have to use it correctly.”

A good metaphor might be another tool, a hammer. You can't just throw a hammer at a nail and expect the nail to be driven into a nearby wall. That would be an amazing throw. No, you have to use the hammer carefully, in a hammering motion, again and again, over a nail carefully pinned between two fingers, thunk, thunk, until the nail is "in the wall." Sunscreen only works when reapplied every two hours, and after venturing into water, and in large quantities—“about a shot-glass worth,” Kundu recommends. But you probably also shouldn’t have a shot glass at the beach, because glass is usually not allowed.

The hammer metaphor is also a metaphor for public-health messages, and how they get into people's heads. Small, strategic bursts of information, hammered again and again, until people know how to choose and use sunscreen. For most people, the main ingredient in sunscreen is good intentions. Which is cute, but doesn't prevent ultraviolet radiation from penetrating their skin and ravaging their DNA.

So as a measure of public health that could prevent many lost lives, conveying sunscreen directly to the public may be worthwhile. In that, Miami is a living, burning experiment. This year alone, the American Cancer Society estimates, 74,000 people in the United States alone will be diagnosed with the most aggressive form of skin cancer, melanoma, that has spread beyond the epidermis. Almost all of those cancers will be caused by ultraviolet radiation. They will result in nearly 10,000 deaths.  

"Skin cancer rates are on the rise despite melanoma being the single most preventable cause of cancer," said the Mount Sinai melanoma program director Jose Lutzky in a recent press statement. "Free sunscreen should be as readily available as public drinking water." Except, just not coming out of dirty fountains. Mount Sinai is funding the refilling of the Miami dispensers for approximately two years, at which point the taxpayers may take over. Or they may not, and the posts on which the dispensers are mounted will rot, and the dispensers will be washed into the ocean and become crab homes.