Exposing your skin to sunlight helps your body to produce vitamin D, which supports healthy bones. Credit: Leopoldo Smith Murillo/Getty
In Defense of Sunlight: The Surprising Science of Sun Exposure Rowan Jacobsen Scribner (2026)
From childhood, science writer Rowan Jacobsen learnt that sunlight is bad news and the main cause of skin cancer, and that its hazardous rays should be avoided. Yet, that’s a one-sided view, as he explains in his provocative book, In Defense of Sunlight. Regular doses of solar energy might benefit our lives, not imperil them.
As easily absorbed as sunlight itself, this vigorous text covers optics, biology, physiology and anthropology. Anyone interested in these fields should applaud its readability, although couch potatoes might find the contents dismaying. Jacobsen fumes at modern indoor lifestyles with the zeal of a “light evangelist”.
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How did we become afraid of sunlight? Well, apparently it wasn’t always so. Roman author Pliny the Elder considered sunshine “the most powerful of all remedies”, and the eleventh-century Arabic Canon of Medicine declared that it “invigorates the brain”.
By 1870, California was promoting itself as The Sanatorium of the World as a second influx of ‘gold rushers’ came to the state, this time to hunt for photons. Europeans later embraced nudism, and US beaches were like “public rotisseries”, and 1920s articles in prominent journals such as Nature and The Lancet established the health benefits of sun exposure. Heliotherapy was happening. And then it wasn’t.
Sunburn fears
During the 1970s, physicians became increasingly alarmed by rising rates of skin cancer. Ultraviolet B rays were initially deemed the radiation responsible, because they shoot energy directly into DNA, altering molecules and causing burns. Hence, early sun-cream products had filters designed to block UVB rays, but they allowed through longer UVA wavelengths.
By the 1980s, scientists had confirmed that UVA photons excite certain skin molecules into a highly charged state. To become stable, these molecules steal electrons from adjacent ones, resulting in molecular damage. Such cellular maiming can result in skin cancer, notably melanoma, the rarest but most serious type.
Early sun creams therefore gave a false sense of security. Users allowed themselves more time in the sun, being shielded against sunburn but not against the UVA that might provoke melanoma. Broad-spectrum sun creams, blocking both UVB and UVA, became more commonplace from the 1990s onwards.
Exposure to the Sun can enrich the skin with beneficial microorganisms that protect against UV radiation. Credit: Koen Suyk/AFP/Getty
Weighing up the pros and cons of sun-cream use poses a dilemma for Jacobsen. It has been effective in reducing the rates of treatable squamous cell and basal cell carcinomas, which form about 99% of non-melanoma skin cancer cases. But photobiologist Brian Diffey and other scientists say that the evidence that sun creams reduce melanoma rates efficiently is still lacking.
Genetics, a poor diet, skin type and sunburns in childhood can all increase the chances of developing melanoma. Jacobsen and Diffey cite factors such as latitude, time of day and time of year as considerations for when to apply sun cream. Many specialists champion clothing and shade as proven protectors, especially for fair-skinned children.
However, Jacobsen’s book analyses sunlight more than it does sun cream, and he goes on to offer many positive perspectives. One study he mentions analysed the skin of lifeguards at the start and end of a summer season during which they were heavily exposed to the sun1. By summer’s end, their skin was enriched with microbial “beneficial bugs” that protect against UV radiation. A square centimetre of human skin contains millions of microorganisms, some of which produce compounds that kill cancer cells without harming normal ones.
Beneficial rays
What is more, people’s over-reliance on vitamin-D tablets is debated. It’s true that rickets, a childhood condition that causes bones to weaken, was suppressed with the help of vitamin-D-fortified foods. However, the disease has risen again among children who spend a lot of time indoors and don’t get enough exposure to sunlight. For people with less than 20 nanograms per millilitre of vitamin D in their blood, taking a supplement won’t do them harm. But sunshine on skin produces vitamin D naturally, in the form of a hormone that helps calcium to get into our bones.
For natural vitamin-D production, skin-cancer specialist Rachel Neale advocates regular short exposures to sunlight, with as much skin bared as possible. Jacobsen therefore proposes that “ten minutes of naked cartwheels in the backyard might not be a terrible idea”.
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Science must also allow for holistic reflection, and Jacobsen observes that without solar energy we would be no more alive than a doorstop. Instead, “we are lumps of mud animated by light and having a conscious experience of the universe”. Going green is also encouraged; forest-bathing people in Japan linked woodland colours to contemplation long ago, and Harvard neuroscientist Rami Burstein found that green wavelengths relieve migraines.
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