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Does sunscreen actually prevent melanoma?

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Slapping on sunscreen is a summer ritual. But are we doing it right? Does it actually prevent melanoma? And what about the claims of “poisonous chemicals”?

We put a lot of faith in sunscreen. On bright summer days, we slap it on and head outdoors, trusting it will protect us from burning or, worse, developing melanoma, New Zealand’s fourth most common cancer.

Melanoma kills 300 of us each year, so the creams, sprays and lotions, produced for the most part by cosmetics companies, are matters of life or death. So it might come as a nasty surprise to learn there has long been a lack of conclusive evidence proving they ­actually do prevent melanoma. The ­cosmetics ­companies certainly haven’t been testing for that and the scientific community has also found it presents difficulties.

Early observations actually reported a higher incidence of melanoma among ­sunscreen users, but there was a problem with the methodology: people with fair skin, those most likely to use sunscreens, are also at greatest risk of melanoma.

“The same thing would happen with hats,” says Australian scientist Adele Green. “Those at high risk are more likely to wear them. But no one in their right mind would think hats cause cancer.”

Green, who is based at Queensland’s Medical Research Institute, has dedicated her career to finding ways to combat skin cancer, and in the early 1990s rose to the challenge of designing a randomised trial to establish whether sunscreen helped prevent melanoma. In a study of 1621 residents of Nambour in Queensland, she randomly assigned study participants either to a ­control group, who were allowed to wear as much or as little sunscreen as they liked, or to a group whose members were given an unlimited free supply and instructed to apply it every morning.

Australian skin cancer scientist Adele Green. Photo/Tony Phillips

The trial ran for five years and the groups were monitored for another 10, at which point the daily users had half the rate of melanoma seen in the control group. Skin ageing was also measured in those under 55 at the start of the trial: the daily users showed 24% less ageing over the five-year period.

“You’re never going to build anything on just one study,” says Green. “But it was a missing piece of the jigsaw.”

The findings are encouraging, but the data on compliance is problematic: Green asked those who had free bottles to return them after three months. The bottles were then weighed to assess how much had been used and the participants sent a fresh supply. Clearly this method of measurement wasn’t going to work with the control group, who were applying sunscreen at their own discretion, so throughout the trial they were asked how frequently they were using it. The trouble is these methods rely to an extent on the honesty or diligence of participants.

Only recently have we been able to cut unreliable humans out of the equation, with the development of animal models. At Ohio State University, molecular biologist Christin Burd has managed to engineer a mouse with genetic mutations similar to a human precancerous lesion, which has allowed her to test the ability of a sunscreen to prevent melanoma.

“It’s really challenging to do these kinds of studies,” says Burd. “A lot of variables come into play. In the US, there are about 30 or 40 different sunscreens with different active ingredients. And then there are the various types of product – lotions, sprays and lip balms.”

Burd chose to test spray-on sunscreens with an SPF (sun protection factor) of 30+, which contained a range of active ­ingredients. These were applied to the mice before 40 minutes of UV exposure. All of the sunscreens were found to delay melanoma onset and reduce tumour incidence.

“It was different for every sunscreen but it was significant for all of them,” says Burd. “One [sunscreen] was even able to negate the effects of UV light completely. I went and bought myself some of that.”

It was then realised the container ­dispensed a larger quantity of lotion than other bottles. This turned out to be a major factor in how well a sunscreen performed and also one of the biggest variables. Even within the same brand, the output through the nozzle was different between bottles. “And as you used the bottle, it changed depending on whether you were at the beginning, middle or end,” says Burd.

US molecular biologist Christin Burd.

Two flavours

Sunscreens fall into two categories: the chemical type absorb UV radiation and release the energy as heat, and  the mineral-based ones –  containing zinc oxide or titanium di­oxide, for example – have particles that reflect UV from the skin (some combine the two). Mineral products used to have an obvious whitening effect on the skin, but in recent years the particle size has been reduced to make them more wearable.

Not many mineral sunscreens are available in spray-on formulas so Burd tested only one and it was among the poorer ­performers. She also trialled a zinc-based cream marketed as a rash treatment rather than a sun protector and it was one of the best. That has led her to theorise that larger particles are better at reflecting light. It may also be that the zinc in the spray-on product wasn’t dispersed consistently throughout the product. Burd can’t say for sure without further testing.

Her initial study used UVB light and now Burd is seeking funding to complete a study with UVA, which doesn’t burn skin but does penetrate more deeply and inflicts long-term damage (it also penetrates through cloud and glass).

Her mouse models have potential beyond that. Burd wants to look at the way the sun changes the immune system and the structure of the skin. She could use mice to explore the chemicals in sunscreens and whether some are better or worse for us than others. And she would like to widen the net, testing more formulas, to find which is the safest and most effective.

“The other question I want to examine is the exact spectrum of light that causes melanoma,” she says. “It may be that specific wavelengths are the most dangerous and we could develop sunscreens targeted at those. So that’s our future aim, to look at small portions of the UV spectrum to see if they have any effect on melanoma risk.”


Animal testing

Cosmetics companies have shown interest in Burd’s research, but she says most are hampered by the fact that, in response to pressure from their customers, they have stopped testing their products on animals and they can’t make an exception for sunscreen, even though its function is far from purely cosmetic.

“Consumers have to ask for better testing,” says Burd, who believes now may be the time to rethink our attitude to this potential ­lifesaver. “They think it is tested and shown to prevent cancer, and that’s not true; the data is limited. There is a place for cosmetic sunscreen, but there needs to be a movement to have some tested for ­medical purposes so people who are at high risk know they can rely on them.”

It’s not as if sunscreens aren’t tested, but questions arise over how often and to what standards the testing is done. In 2014, Consumer NZ independently tested 12 sunscreens and found seven of them didn’t meet their SPF label claim. Chief executive Sue Chetwin says a major issue was cosmetics companies were relying on old results.

“There is no pressure on them to keep ­testing the batches to make sure the SPF hasn’t changed,” she says. “One company was still relying on results from 2009. Another problem, we believe, is a reliance on overseas labs’ [results], although that is hard for us to prove. Essentially we think there should be proper auditing of these labs.”

Some regulation may be beneficial, too. “It astounds us that sunscreens are still classified as cosmetics,” says Chetwin. “Pretty much anything goes here.”

Companies are “en­­couraged” to meet the voluntary Australian and New Zealand standard for sunscreen, but they are free to sell products here that meet European or US standards – or no standard at all. Meanwhile, in Australia, sunscreen is regulated as a therapeutic product.

Chetwin says Consumer NZ would like to do more independent testing but, having lost Ministry of Health funding, it is looking for other ways to pay for what is an expensive process. “We’re the only ones out there that are doing it, and in a country like New Zealand, that is at such high risk of melanoma, it just seems a no-brainer.”

Photo/Getty Images

The producer of our second-highest-­selling sunscreen is Daffodil Enterprises, the commercial arm of the Cancer Society. It chose to meet the Australian and New Zealand standard, but the real-life situations in which we rely on sunscreen are difficult for it to replicate in a laboratory.

“Scientists don’t don togs and play volley­ball or all these other things we do in our sunscreen – as fun as that would be,” says Daffodil’s general manager, Fiona Mawley.

Instead, the testing of UV protection levels involves a minimum of 10 volunteers, between the ages of 16 and 70, with skin ranging from naturally fair to light brown. They have a measured amount of the product applied to a marked-out area of skin. It is evenly spread and allowed to dry for 15-30 minutes before the skin is exposed to a solar simulator (resistance to water and sweat are tested using spa baths and exercise bikes).

Compare all that with the haphazard way most of us slap on our sunscreen and it is already clear why the protection we get may not match what it says on the bottle. Companies report consistently finding that, when consumers complain of getting sunburnt, poor application is at the root of the problem.

“The average person should use a 35ml application (about seven tea­spoons) for the whole body – we suspect most use far less than this,” says Mawley.

Sunscreen that has chemical active ingredients must be applied at least 20 minutes before exposure to the sun and needs to be reapplied at least every two hours to maintain the protection rating shown on the bottle. Again, in the world outside the lab, we’re often not playing by the rules.

Some people have become spooked by  scare stories about chemical filters. Five years ago, supermodel Gisele Bündchen infuriated experts by saying of sunscreen, “I cannot put this poison on my skin.” She was launching her own skincare line at the time and later, on her blog, clarified her original statement, saying she did use sunscreen but tried to choose “more natural options”.

More recently, TV’s My Kitchen Rules chef Pete Evans told his 1.5 million Facebook followers that people who used sunscreen were “covering themselves in poisonous chemicals”.

Some sunscreens’ active ingredients can cause allergies and there have been concerns about chemical UV filters acting as hormone disruptors. A 2010 study by Swiss scientist Margret Schlumpf showed in lab tests that a number of chemical filters mimicked the effect of oestrogen and also found six out of eight of the filters she analysed in human breast milk.

This information has been jumped on by well-being websites with a fondness for headlines that shout about “killer sunscreen”, despite the fact Schlumpf didn’t recommend people stop wearing sun protection altogether since there is no proof the chemicals harm health and plenty of evidence  UV radiation causes cancer. However, she was concerned about the danger that strict protection against skin cancer may cause in vitamin D deficiency and how best to find a balance.

Solar D’s Mathew Collett.

Vitamin d problem

Up to 90% of the vitamin D we need is formed in the skin through exposure to the sun – specifically UVB rays. It is also found in foods such as fatty fish, liver and eggs, but it would be hard to get enough through eating those things. Low levels of the vitamin have been linked to a number of conditions, including some cancers and dementia, and it is vital for bone health.

Most people don’t need a huge amount of sun exposure to produce adequate vitamin D. In fact, the body switches off production once levels have been topped up. In this country, just a few minutes of exposing the unprotected face, arm and legs in the summer months is enough, and in the winter a daily walk or other activity is advised (physical activity has been associated with increased vitamin D levels).

Some New Zealanders have been found to be vitamin D-deficient, particularly in more southern areas over the winter months. The high-risk groups for deficiency are darker-skinned ethnicities and the elderly. For these people, and anyone else concerned, there is now an alternative to taking supplements. Solar D is a new-generation sunscreen designed to protect the skin from damage while still allowing synthesis of vitamin D.

When applied properly, a normal SPF30 sunscreen reduces the capacity of the skin to produce vitamin D by almost 98%. Research commissioned by Solar D’s makers found its adjusted formula allows 50% more production. Now in its second summer on sale in New Zealand, Solar D permits increased transmittance of UV radiation from 290-300nm (UVB) while maintaining high levels of protection from UV radiation outside that range.

“We’re going into our third summer in Australia and we haven’t had a single ­complaint of people being burnt,” says Solar D’s founder and managing director, Mathew Collett. “We can prove the science behind it. We know there is a certain ray and we know it lets in that ray. We don’t guarantee people will produce vitamin D as that is a therapeutic claim we can’t make.”

Testing in an independent laboratory, comparing Solar D with 11 other sunscreens, found some did the exact opposite. They ­filtered out the rays we use to produce vitamin D and let through some of the harmful ones.

Our ageing skin

Opponents of sunscreen note skin cancer is on the rise even though sunscreen is being used more than ever. But our ageing population had high sun exposure during their youth and now, as their immune systems are flagging, the cumulative damage is showing.

In a bid to prove it’s the early years of sunscreen use that are crucial, scientists at the Texas Biomedical Research Institute have developed another animal model – this time using opossums. Infant opossums treated with an SPF15 lotion showed 90% fewer pre-malignant lesions than those that didn’t get any sun protection. This difference occurred even under low doses of UV light that caused no reddening of the skin.

Researchers speculate it is particularly important sunscreens be used consistently in childhood and infancy, because skin cells are dividing much more rapidly than in adulthood, and it is during cell division that the cells are most susceptible to UV-induced damage.

That doesn’t mean that, if you are older, you don’t need to bother with sunscreen or it is too late to get any benefit. Palmerston North dermatologist Louise Reiche says her 20 years of clinical practice have shown her how important sunscreen is later in life.

“When patients take the sun protection advice on board, it’s ­phenomenal,” she says. “Even though they might be at high risk and I may be excising skin cancers every month, when they start wearing hats and being diligent about sunscreen, they stop growing as many skin cancers and their skin starts looking younger and healthier. I’m seeing that happen first-hand and I’m seeing it more quickly now because sunscreens have improved and are broader-spectrum and higher SPF.”

Palmerston North dermatologist Louise Reiche.

False confidence

A danger of sunscreen is it gives fair-skinned people the confidence to spend far longer outdoors than they should.

“There is a misbelief that sunscreen is the ultimate protection,” says Reiche. “Years ago, we called it sunblock, but we stopped that because it doesn’t block the sun, it’s a filter. You still get sun coming through.”

Lab tests have shown SPF15 sunscreens filter out 93% of UVB rays, whereas SPF30 protects against 97% and SPF50 against 98%. But New Zealanders tend to spend all day outside and sunscreen can’t cope with that, says Reiche. She encourages people to cover up with high-UPF (ultraviolet protection factor) protective clothing, sunglasses and hats, and to use sunscreen on the bits left exposed.

“If you hold up a garment to the sun and can’t see any light coming through, then the sun probably can’t [penetrate it],” she says. “But the advantage of UPF-rated clothing is new-technology fabrics provide airflow as well as sun protection.”

A suntan, once thought of as healthy, is now known to be a sign of DNA damage. Some sun lovers, though, won’t have a bar of the pale-is-good message.

“I have a group of patients that had a lot of sun exposure in the 1950s and 1960s. Some say they still can’t help it, they love being out in the sun and having a tan; it has positive psychological effects. These people are addicted to tanning,” says Reiche. She is backed up by work at Harvard University, where scientists experimented with mice to prove sunlight stimulates the body to release endorphins, which trigger positive feelings.

Most of us, though, don’t fall into that camp. We might be a bit slapdash about application but we have the best intentions when it comes to protecting our skin and that of our families.

Ohio University’s Christin Burd says when she suntanned her genetically engineered mice for just 40 minutes without any sort of protection, they soon developed moles and the rate at which these became  melanomas was faster.

“That’s scary,” she says. “How many times do we think, ‘Oh, it’s just once; it won’t matter.’ But these mice got just 40 minutes.”

Burd, like the rest of us, wants to buy a product that is safe and effective, that cuts her risk of skin cancer, and has been developed and tested based on what people really apply.

“When I go into a store I have an anxiety attack with all these different options. You would never think something as simple as sunscreen could be so complicated.”

Photo/Getty Images

Sunsmart phone

Niwa data has been used recently in the development of a UV index (UVI) app called “uv2Day”. The app provides UVI forecasts, with and without cloud effects, throughout the day at the nearest location, or at other selectable locations. The app includes behavioural ­messages, and is useful for planning activities to optimise sun exposure throughout the year, and for educating the public on what the UVI means.

This article was first published in the January 7, 2017 issue of the New Zealand Listener. Follow the Listener on Twitter, Facebook and sign up to the weekly newsletter.