I GREW up in Queensland, Australia, which is, to put it mildly, a very sunny place – and, to put it bluntly, the skin cancer capital of the world, with a higher incidence per capita than anywhere else. As a pale-skinned person, I have experienced a blistering case of sunburn more times than I would like to admit and I know that for Caucasian people, even one instance more than doubles the risk of getting melanoma, the deadliest form of skin cancer. Sunscreen, then, is my constant friend.
Lately, however, I have been worrying that being sun-smart may have unintended consequences. I have heard that the chemicals in sunscreen could be harming coral reefs, and maybe even our own health. So I was curious – not only about the extent to which these concerns are really justified, but also whether science is any closer to producing safer and more effective sun creams.
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I found that although the evidence for sunscreen’s harmful effects is patchy and conflicting, a new generation of preparations is emerging from laboratories. Many are based on compounds found in algae, plants and even coral, and they are being formulated in ways that promises to solve the problems with today’s products. In one case at least, there is even the prospect of a sunscreen you truly won’t have to laboriously reapply throughout the day.
When sunshine beats down on us, we are getting a dose of two types of skin-damaging ultraviolet light, called UVA and UVB rays. The former are the less energetic of the two, but penetrate deeper into our skin, where they can create chemicals called reactive oxygen species (ROS). These compounds, sometimes also called free radicals, are highly chemically reactive and they damage crucial enzymes in the skin as well as support structures, such as those made of the protein collagen, leading to premature skin ageing. The more energetic UVB rays, meanwhile, directly distort the shape of DNA. If too much of this occurs, it can lead to genetic mutations and skin cancer.
All this happens to some extent any time our skin is exposed to the sun. People with black or darker skin have more natural protection because their dermal cells contain more melanin, the body’s sun defence mechanism. But whatever your skin colour and whether or not you tan or burn, excessive sun exposure can be damaging. “UV-based DNA damage can accumulate over time even without sunburn,” says at the University of Queensland.
The symptoms of sunburn – the pain, redness and hot sensation – aren’t a direct result of the UV rays, but rather due to your immune system kicking in. Cellular messaging summons an influx of cells to clean up and repair the damage, and blood vessels leak into the spaces between cells, causing swelling and redness. The inflammatory reaction peaks after one or two days, which is why the pain can increase long after you go inside.
Chemical or mineral defences
To avoid this sorry state sunscreen is a must, especially as covering up with clothing often isn’t practical. Sunscreen comes in two basic types. First, there are mineral sunscreens that contain zinc oxide and titanium dioxide and protect skin partly by reflecting away UV rays. They are often recommended for people with sensitive skin, largely because the particles of these chemicals are too big to penetrate the skin. However, they can feel heavy to wear and leave a noticeable white residue, particularly on darker skin. These might sound like minor gripes, but if discomfort discourages you from wearing sunscreen, that is a major problem.
Then there are chemical sunscreens, which use carbon-based molecules as their active ingredient. Common examples include avobenzone, oxybenzone and octocrylene. These molecules absorb UV rays and radiate their energy away as heat. Alongside them, chemical sunscreens also often include molecules called antioxidants that can neutralise free radicals that damage the skin.
Chemical sunscreens tend to feel lighter and don’t whiten skin and, as such, they dominate the market. But the small size of the molecules means they can penetrate the skin. That presents several potential problems. It means chemical sunscreens can irritate the skin and they may become less effective as the molecules are absorbed.
The big worry is that chemical sunscreens might cause health problems when absorbed into the bloodstream. Animal studies and preliminary human data indicate that . “There are still many issues with multi-component sunscreen formulations,” says .
In most countries, sunscreens are treated like cosmetics, but in the US they are regulated like medicines by the Food and Drug Administration (FDA) and are subject to more scrutiny. The FDA recognises mineral sunscreens as safe, but, in 2019, it updated its guidance to say more information is needed on chemical versions. This means that the FDA doesn’t have enough data on the long-term effects of these compounds in the bloodstream to pronounce them safe.
But this doesn’t mean the chemical formulations are unsafe either. On the other hand, UV damage is conclusively harmful, so dermatologists don’t want people to stop using sunscreens. “At present, there is no convincing data to show that chemical sunscreens are harmful for human health,” says dermatologist at the University of Texas at Austin. Any such potential threat should also be set against the very real risk of cancer. In the UK alone, melanoma cases have reached an all-time high of 17,500 per year, according to recent figures from Cancer Research UK.
Environmental concerns
When it comes to environmental concerns, the main one is that sunscreen kills coral reefs. But while show that sunscreens are toxic to coral, scientists say this pales into insignificance compared with the damage done by pollution, invasive species and climate change. The other thing is that these studies don’t mimic how sunscreens spread from skin to reef water and onto corals, and they use massively higher concentrations of sunscreen ingredients than have ever been measured on an actual reef.
In any case, new developments could alleviate the concerns. One proposal is to take chemical sunscreen agents and encapsulate them in tiny, bubble-like structures that stick to skin. That way, the sunscreen wouldn’t be able to penetrate the skin or wash off easily – which would also save you from having to reapply quite so often. Biomedical engineer at Yale University and his team have invented a non-penetrating sunscreen by encapsulating avobenzone and octocrylene in bioadhesive nanoparticles. In 2018, a study , and the group is now running a designed mainly to check the cream’s safety.
Besides using existing ingredients in smarter ways, researchers are also looking at new sunscreen molecules, many of which come from nature. One surprising example is lignin, one of the main biochemicals in trees and most other plants, which is UV-protective and a highly renewable resource. Its dark colour can stain skin and fabrics, though, so researchers are still exploring how it can be chemically tweaked to make it suitable for slathering on our bodies at the beach.
Inspired by nature
Inspiration also comes from the sea. Twenty years ago, microbiologist at King’s College London gazed out at Australia’s Great Barrier Reef and wondered why the corals didn’t appear to get sunburn. It turns out that corals and other organisms like algae produce their own natural sunscreens called mycosporine-like amino acids (MAAs). Long and his colleagues were the first to demonstrate that palythine, an MAA extracted from a red seaweed, . Palythine also has antioxidant properties and can even stimulate a cell’s own antioxidant defences. “These are amazing molecules,” says Long. There are no MAA sunscreens on the market yet, but studies that added MAAs to commercially available versions .
Perhaps the most innovative new sunscreen idea takes inspiration from the body’s own sun protection, melanin. Polydopamine (PDA) is a synthetic molecule that mimics the chemical structure of melanin and has been shown to protect skin cells in similar ways. “PDA has huge potential as a UV-protecting material, [working] as natural melanin does in the living organism,” says at the University of New Hampshire, who has been studying natural and synthetic melanins and their applications for over a decade.
The reason PDA is so useful is that it acts as both a UV filter and a free radical scavenger, so sunscreen formulators wouldn’t need to add extra antioxidants. Yiwen Li and at East China Normal University are working on how to disperse PDA nanoparticles in gels. They recently produced a non-penetrating PDA gel with a very high sun protection factor (SPF) of more than 100 that for 6 hours in tests on mouse skin. The process to start a human clinical trial is under way. PDA sunscreens could be available on the Chinese market in the near future, Li and Cheng reckon, but the path to certification elsewhere – especially in the US – could take longer.
All of which sounds promising. Some mornings, though, I wonder if there might be an easier way to protect against the sun than slopping on lotion – like taking a sunscreen pill, for instance.
There is already a drug called afamelanotide () that effectively turbocharges the skin’s tanning ability. It works by stimulating a hormone that, in turn, triggers skin cells to release melanin when exposed to sunlight. The drug-induced tan screens out some skin-damaging UV wavelengths. However, it is currently only prescribed for people with photosensitivity conditions and it isn’t a pill – it is injected as an implant under the skin and needs topping up every two months or so.
For those just looking for a sunscreen top-up, researchers are investigating the photoprotective properties of certain vitamins and botanicals. These include classic candidates like carotenoids (pigments found in tomatoes, among other places) and green tea polyphenols. Early studies , by preventing DNA damage and by boosting immune responses, or a combination of these mechanisms.
Fern extracts
Then there is the curious case of an extract from the tropical fern Polypodium leucotomos. Dermatologist at the University of Alcalá in Madrid, Spain, has been studying this extract, called PLE, since the 1990s. When taken in supplements or applied topically, PLE has been shown to protect skin against DNA damage, neutralise free radicals and prevent the depletion of certain skin cells, a recognised cause of skin cancer.
Popping a PLE pill will never be equivalent to applying sunscreen. González did a study in 1997 that found a dose of about 1000 milligrams of the extract equivalent to an SPF of just 3. But he says that people with fair skin or those with a high risk of photoageing could use it as part of a daily skincare regime and it could help stave off the effects of low-level sun exposure.
That makes me wonder about vitamin D. This crucial nutrient is largely created in the body in a way that depends on sun exposure, which suggests that constantly shielding ourselves could worsen the deficiency many of us already have. A of several studies, however, found that using suncream isn’t correlated with lower levels of vitamin D.
Personally, although it is good to know that we might soon have some new and better options when it comes to sunscreen, for now I will keep slip-slap-slopping on the stuff we already have. After all, the best kind of sunscreen is the one you actually use.
Larissa Fedunik is a science writer based in Sydney, Australia
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