We deserve a better sunscreen. Once you dutifully rub the average lotion over every inch of exposed skin, it only lasts for a short while—maybe an hour or two at the most, according to the American Academy of Dermatology—before you have to smear it on all over again. Even if you're diligent about sunscreen use, you can still end the day with a nasty burn. And while a sunburn is painful enough on its own, the underlying UV damage to your skin can lead to potentially fatal skin cancer.
Every health organization and doctor says you should wear plenty of sunscreen, and there's little doubt that it can reduce your risk of melanoma, the most dangerous skin cancer. A long-term study found that people who wore sunscreen and took a beta-carotene antioxidant supplement daily for four years cut their risk of melanoma in half over the next ten years. Of course, that's if you use sunscreen every day, and includes the free-radical-fighting boost from the antioxidant supplement. A 2016 study of more than 140,000 women in the high-latitude, short-summer country of Norway found that using sunscreen with an SPF of 15 or more while tanning or being out in the sun reduced melanoma risk by 18 percent.
But then there are other skin cancers sunscreen doesn't necessarily protect against. In an extensive review published last year on sunscreen and the risk of basal cell and cutaneous squamous cell carcinoma, which are less likely to spread to other parts of the body than melanoma but make up 95 percent of malignant tumors, found only one strong randomized clinical trial–and that trial showed no benefit to sunscreen use. The review ultimately determined that there wasn't enough evidence to say that sunscreen prevents non-melanoma skin cancers, while the study authors advised that "patients and consumers do not stop protecting their skin until better quality evidence emerges."
So what's standing in the way of a better, more reliable sunscreen? A complex set of molecular challenges, basically. But science has been building momentum towards a product that protects from a wider variety of skin cancers for more than just a couple hours at a time.
There are two types of compounds in sunscreen that do the hard work: minerals like zinc oxide that block ultraviolet (UV) radiation, and UV absorbers. These absorbers are able to take in the energy from the UV rays and use it to jump up into an excited energy state, like a supersonic jet hitting the afterburners. Absorbing the energy prevents the UV rays from scorching your shoulders and causing DNA damage that could lead to cancer.
After a short time, those excited molecules drop back down to their initial energy state and release their stored energy as heat. "You feel your skin warming up in much the same way it does when your natural photoprotection molecules absorb UV," says Vasilios Stavros, a photochemistry researcher at the University of Warwick in England. (Heat from the sun, it should be said, does not cause sunburns. The redness and inflammation is your body's immune response to excessive UV damage.) Once the absorber returns to its original energy state, it's ready to soak up more radiation.
That's how sunscreens should ideally work. In reality, sometimes the absorbing chemicals can get "stuck" in a high-energy state. Once that happens, they'll never absorb radiation again. As more and more absorbing molecules get stuck, and as you lose sunscreen to sweating or swimming, your protective lotion becomes useless and it's time to squeeze more out of the bottle onto your skin.
And even when sunscreen molecules do successfully release the stored energy and return to the proper energy state, it isn't always in the form of heat, or vibrational energy. "It can react and potentially generate radicals," Stavros says. "These can be very harmful." The free radicals could cause skin rashes (essentially, a sunscreen allergy) or further damage the DNA in your skin cells.
One big question to researchers like Stavros who are working to develop better sunscreens is why, exactly, the compounds that are supposed to absorb radiation either fail or suddenly spew out free radicals. So far, science hasn't been able to provide answers. "We have known for decades that molecules interact with light and absorb this radiation. Some molecules are very good filters of UV and these molecules were used in formulations," Stavros says. "Much of the work is trial and error based, albeit with standardized testing, but it is not unsurprising given the complexity of the processes at the molecular level."
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Scientists are now delving into how these molecules operate using high-energy lasers to identify energy states and determine how the molecules respond to radiation. But to achieve broad UV protection, the sunscreen you buy could be made from any of several different classes of chemical absorbers, and each one functions differently. Once those compounds are understood on an individual basis, scientists will then need to analyze how these chemicals work in concert when they're mixed together in a sunscreen formulation, which raises the complexity by orders of magnitude. "This is pretty much the tip of the iceberg," Stavros says. "We really lack a molecular understanding of the highly complex and even simple blends, and to achieve such understanding—which will then enable us to facilitate design of new and improved sunscreens—will take many years."
At the same time, some new ideas about how to protect humans from the sun are inching closer to reality. A good portion of innovation has stemmed from the observation that plenty of plants and animals live under the open sky with no need for sunscreen, and don't seem to suffer the harmful effects of UV rays. By identifying the compounds that provide natural sun protection to, say, algae or fish, researchers hope to create commercial products with those same benefits.
One source of natural UV absorbers are cyanobacteria, which use photosynthesis for energy but are distinct from algae. The bacteria produce their own amino acids to protect from UV damage, with some studies showing that the compounds are effective enough to prevent 90 percent of UV rays from penetrating the organism.
Another option might be to skip smearing on sunscreen entirely and instead take a pill. The pill would be effective for longer than a sunscreen lotion, and because it would affect your whole body, you wouldn't have to worry about missing a spot or finding someone to rub the cream on your back.
It's an idea that's been around for a long time, which is why people in the studies mentioned earlier took a beta-carotene antioxidant supplement. And you may see antioxidant supplements on the shelves now that claim to protect your skin against free-radical damage. Those aren't a substitute for sunscreen—at least not yet.
But the amino acids produced by cyanobacteria and other organisms might just be effective enough to one day make a true pill-based sunscreen. One compound, called gadusol, works as both an antioxidant and a UV absorber. "It is believed that gadusol is non-toxic and can be taken orally, which seems more convenient, has systemic effects, and the compound cannot be easily washed by water," says Taifo Mahmud, a professor of pharmaceutical sciences at Oregon State University. Mahmud published a study last year detailing how gadusol could be produced on an industrial scale by cultivating it in yeast.
Although scientists have been exploring this area for years, it will probably be even longer before a gadusol sunscreen pill is developed. And it may turn out that a better lotion is still the best solution. "There is no study on its absorption, distribution, metabolism, and excretion in the body. So, we don't know if the compound will be absorbed and distributed to the skin or not," Mahmud says. "So, for now, lotion is still the most feasible option."
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