This article is part of a special issue investigating key questions about skincare. Find the full series here.
Even if we live far from the equator, we are often told to apply sun protection factor (SPF) lotions year-round to protect our skin from premature ageing and wrinkles. But is this backed up by solid science?
Just of US adults use SPF creams as part of their daily routine, according to one survey. That is clearly a problem in the summer, when the sun is brightest. While we may not show signs of burning, UV rays can penetrate the deeper layers of skin and damage it. Besides contributing to wrinkles, this can lead to skin cancer 鈥� and people who wear sunscreen are at a much lower risk of this.
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Photoageing is a cumulative effect that adds up over the decades
However, these rays are much weaker in winter at more northerly or southerly latitudes, and the benefits of SPF must be balanced against the costs. , an emeritus professor of photobiology at Newcastle University in the UK, points out , for example. SPFs can also have an environmental cost, with some studies showing that they can wash into the oceans, where their component chemicals can be absorbed by corals and other marine life, harming them.
Diffey to calculate how much UV light a typical person living at different latitudes in the northern hemisphere is exposed to every day of the year, taking into account the fact that most people living in more northerly places work indoors and spend considerably less time outdoors in the colder, winter months.
He concluded that for a person living at latitudes of 45掳 north and higher, which includes vast swathes of North America and Europe, almost all UV exposure comes during the summer months, making sunscreen during winter unnecessary. 鈥淭here鈥檚 no point using a sunscreen when it鈥檚 not doing you any good, and all it鈥檚 doing is potentially increasing the risk to yourself and the environment,鈥� he says.
Snowballing effects
As London sits at a latitude of 51掳 north, Diffey argues that people there can safely go without sunscreen from October to early April. 鈥淥n a typical winter鈥檚 day, an indoor worker in the UK gets the equivalent of about 1 minute of summer sunbathing,鈥� he says. Residents in New York, which lies at around 40掳 north, can only go SPF-free from November to February, according to Diffey鈥檚 calculations. And those living at latitudes of 30掳 north or lower should wear sunscreen all year.
While other experts agree that the potential for sun damage is much lower in the winter compared with summer, they argue that even small effects can become a problem over time. 鈥淧hotoageing is a cumulative effect that adds up over the decades,鈥� says at the Leibniz Research Institute for Environmental Medicine in Germany. 鈥淪o, if you use a product which provides protection against UVA and you do this every day, then by 40 you will look significantly younger than somebody who didn鈥檛 do this.鈥�
, a dermatologist at McGill University in Montreal, Canada, agrees that the benefits of using SPF in winter outweigh any potential risks. Sunlight triggers the production of in the skin, but the amount produced at higher latitudes at this time of year is negligible, he says 鈥� and it can easily be remedied with supplements. Anyone with a family history of melanoma, with very fair skin or who is taking immunosuppressants or medications that make you more sensitive to UV light should always wear sunscreen, he advises.
鈥淚 have patients who are 104 and they鈥檙e getting skin cancer, not by frying on sun loungers, but just by doing regular activities,鈥� says Litvinov. 鈥淪o, if you鈥檙e fair-skinned and you want to live to [that age] then, by golly, you should be more robust in terms of your sun protection measures.鈥�
