At first, it looks like human artifice – a Photoshopped demonstration of ageing in action. But the image of truck driver William McElligott is actually a stark reminder of the destructive power of the sun. The left-hand side of the 66-year-old's face is deeply lined, pitted and sagging after 28 years of sun exposure through the side window of his lorry. The right-hand side, shaded by the cab as McElligott delivered milk around Chicago, is the taut, unblemished face of an apparently much younger man.

McElligott didn't notice the developing asymmetry for 15 years and only sought treatment when his grandchildren asked him about the "bumps" on his face. Doctors were shocked, and his image was published in the New England Journal of Medicine as a striking example of unilateral dermatoheliosis, or photoageing, caused by prolonged exposure to UV rays. The image demonstrates the danger to workers who might not regard themselves as at risk from the sun, according to Gill Nuttall, chief executive of Factor 50, a support group for people with skin cancer. Nuttall has written to Brendan Barber, general secretary of the TUC, urging unions to help raise awareness of the risks for workers, including those such as meter readers, taxi drivers and even sales reps who don't regard their job as being outdoors. "They don't perceive themselves to be in any kind of danger," she says.

She has seen severe sun damage on the hands of reps – exposed to sun through windscreens — who drive for a living because car windscreens do not protect from UVA rays. These rarely trigger obvious sunburn, unlike UVB rays, but cause most photo-ageing, and can also lead to skin cancer. Just as images of smoking-induced wrinkles have been used to appeal to the vanity of the young so charities hope that real images such as that of McElligott could shock people into protecting themselves. Skin cancer charity Skcin has used a similarly shocking illustration of the ageing effects of the sun in identical twins, one of whom worked outside all her life and one who worked in an office, in presentations. "It always generates a gasp," says Charlotte Fionda of Skcin. The image of McElligott might also have an impact on men who would otherwise not be worried by a few wrinkles, according to Fionda – provided people trust that the image is not fabricated.

"The ageing bit is the one thing that makes people more aware and likely to take action - because they think skin cancer will never happen to them," she says.

"The imagination is a very powerful thing," adds Nuttall. "It doesn't take much to imagine one's own skin in 20 years' time — William's story is one we are going to see again and again."