By Chiamaka Egwu
Even weak sunlight can damage human skin at the DNA level and potentially contribute to skin cancer over time, scientists have warned, challenging the belief that early morning and late afternoon sun exposure is largely harmless.
A landmark Australian study by researchers at QIMR Berghofer Medical Research Institute found that ultraviolet, UV, radiation doses too low to cause visible redness could still trigger measurable DNA damage in skin cells.
The findings were published in the scientific journal Photochemistry and Photobiology.
The researchers said the findings showed that the total dose of UV radiation received, rather than simply the intensity or duration of exposure, is critical in determining skin damage.
Study co-lead, Professor Rachel Neale, said people could receive the same amount of UV radiation either during a short period of intense sunlight or over a longer period when sunlight was weaker.
“You can get the same dose of UV radiation in a short time in the middle of the day or a longer time earlier or later in the day. Our research has shown it is the total dose that is important — it doesn’t matter how long it takes to get it,” Neale said.
The Low-Dose UV Study involved 58 people with light to olive skin. Researchers exposed an area of each participant’s back to different levels of UV radiation corresponding to conditions such as mid-morning and lunchtime sunlight over several days.
Skin biopsies were subsequently taken to assess DNA damage as well as molecular and immune responses.
Damage without sunburn
The researchers said they were surprised to find evidence of DNA damage regardless of whether the UV dose was delivered over a shorter or longer period.
Importantly, the exposure was not sufficient to cause the participants’ skin to turn pink, yet measurable DNA damage was detected.
Study co-lead, Professor David Whiteman AM, stressed that the finding did not mean cancer had already developed in the participants.
“Our lab results show these small, incremental doses of UV have caused some damage to the DNA in the skin cells, enough for the cells to then respond to the damage,” Whiteman said.
He explained that repeated episodes of incidental UV exposure could accumulate over time.
“Over months and years, these episodes of incremental, incidental UV exposure will have a cumulative impact on the skin and can lead to mutations that will initiate skin cancer,” he said.
The researchers examined molecular warning signs of skin damage, including p53, a protein that increases when skin cells are stressed or their DNA is damaged, as well as UV-induced DNA lesions.
Rethinking ‘safe’ sunlight
The study challenges the long-standing assumption that spending time outdoors when sunlight intensity is relatively low is necessarily safe for the skin.
However, the researchers stressed that their findings were not a call to avoid sunlight altogether, noting that sunlight also plays an important role in vitamin D production and overall health.
Instead, they said sun-safety guidance should increasingly reflect biological evidence about cumulative UV exposure.
Sunlight is classified as a complete carcinogen because it can both initiate and promote cancer. Current guidance recommends sun-protection measures when the UV Index reaches 3 or above.
The researchers said their findings also supported incorporating sunscreen into daily routines, particularly because people can accumulate UV exposure during brief and unexpected periods outdoors.
“Our aim is to give Australians accurate, trustworthy guidance,” the researchers said, adding that understanding whether sunlight considered “safe” is genuinely risk-free at the cellular level is important for effective prevention.
