Is everything we know about suncream wrong?
Hippocrates was a great advocate of the sun's healing properties. In the mid-20th century, after sunlight was shown to treat rickets, 'sunray therapy' - via ultra-violet lamps - was even widely championed across the UK as an antidote for everything from throat infections to acne.
But in recent decades, a cloud has been cast over the sun's health benefits. It began with Australia's Slip! Slop! Slap! campaign in 1981, which encouraged the public to slip on a T-shirt, slop on some suncream and slap on a hat to reduce the country's rising rates of melanoma, the deadliest form of skin cancer, linked with UV radiation.
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The campaign worked, was mimicked across the world, and created a billion dollar industry: global sales of suncare reached €14bn in 2015 and are predicted to hit €22bn by 2024. And gone are the days of buying factor 15: sales of factor 50 are rising and you can now buy SPF100, as well as face creams and make-up that also contain SPF.
But are suncreams as healthy as they seem? Researchers from the US Food and Drug Administration (FDA), led by Dr David Strauss, recently found that chemicals in suncream can make their way into the bloodstream at levels up to 419 times what is considered safe. The study was small - just 24 people - but their findings have led to plans for a larger trial.
The researchers looked at four active ingredients found in many suncreams, including oxybenzone, octocrylene, avobenzone and ecamsule. They found the chemical oxybenzone, which absorbs UVA rays, reached plasma concentrations of up to 209.6ng/mL, despite the FDA recommending products contain no more than 0.5ng/mL to prevent cancer.
"I'm aware of the paper," says Dr Andrew Birnie of the British Association of Dermatologists. "I read it and then I read the headlines, and then I sighed because there's a risk that what people will take away from this study is not to use suncream because it causes cancer, when the reverse is true. So we need a degree of balance."
The study involved huge doses of suncream, equivalent to applying it across some 75pc of your body, every two hours, for two weeks
"In practice, few people do this, and if they do, they [only] do it for two weeks. Even then, the body is very good at filtering out bad things. So this study isn't a major concern for me at this stage, although there are plans for more research," says Dr Birnie. "We have known for years that certain chemical sunscreen filters are 'lipophilic' and thus are absorbed easily into the skin - this is one of the reasons they are so good at filtering UV light," says Paul Banwell, a consultant plastic surgeon and founder of Melanoma And Skin Cancer Unit in the UK.
"Similarly, we have also known that they are absorbed into the body. Previous studies have shown no adverse effects from this and the American Academy of Dermatology have declared that oxybenzone is safe to use.
"It's similar to the burnt toast theory: burnt toast was linked to cancer, but in reality, you'd have to eat an awful lot of it to see an increase in risk. Likewise, this study used excessive amounts of sunscreen with repeated applications - very much over and above what would be considered normal for sunscreen use. The bottom line is that sunscreen is the single most important factor in skin cancer prevention that we have available to us."
There's also the issue of vitamin D, which is made when the skin is exposed to sunshine - with many Irish people having low levels, which some experts link to our overzealous approach to sun safety.
"For years, public health advice has been to stay out of the sun and wear a high factor suncream at all times to cut the risk of getting skin cancer, and for good reason," says dietitian Helen Bond. "However, most of us spend a lot of time in offices during daylight hours, meaning our skin is never exposed to the stronger UVB rays needed to make vitamin D. Consequently, we don't make enough to stay healthy all year round."
That matters because virtually every cell in the body is affected by vitamin D: as well as maintaining healthy bones and teeth, it promotes healthy muscle function and strong immunity. "On top of this," says Bond, "there has been a lot of new research suggesting it may help protect against some cancers, Type 1 diabetes, cardiovascular disease, age-related macular degeneration, mental decline and rheumatoid arthritis.
"There's no one-size-fits-all on the precise level of sun exposure you need to top up your vitamin D. But experts suggest exposing our hands and face, unprotected, to the sun for 15 minutes a few times a week during spring, taking care not to burn. And in the summer, for 10 to 15 minutes at least three times a week. As with all other areas of health, a little balance - or in this case, a little sunshine - is good."