HOW HAS the sun, long seen as a source of life and wellbeing, come to carry a health warning? Thanks to public health campaigns, skin cancer is now widely perceived as sun cancer. Yet the relationship between exposure to sunlight and the risk of skin cancer seems more complex and controversial than the Department of Health and others would have us believe.

Perhaps 85 per cent of skin cancers in Britain are basal-cell or squamous-cell carcinomas. These are definitely related to the sun’s UV rays; they are also easily treated and rarely serious. The other form of skin cancer — malignant melanomas, or moles that become cancerous — is far more dangerous. Although melanomas account for a relatively small percentage of skin cancers in the UK, they cause the vast majority of deaths: around 1,650 in 2001.

Malignant melanomas are the focus of public anxieties and campaigns about avoiding exposure to the sun. Yet they are the form of skin cancer least clearly explained by the effects of sunlight alone. Most melanomas appear on areas of the body that are exposed to the sun only intermittently. Among men, more than a third develop on the trunk; among women, almost half are found on the legs. In Brisbane, Australia, an office worker is more likely to develop a melanoma than a brickie toiling in the sun.

It could be argued that this is because a brickie becomes acclimatised to the sun’s rays, whereas an office worker is more likely to get sunburn on holiday. Just last week, after a young student died of a malignant melanoma, doctors claimed that her cancer could have been triggered by one day’s severe sunburn.

This view has also been used to explain the fact that melanomas often appear on parts of the body exposed to sun only intermittently. But it is nonsense, according to Professor Jonathan Rees, head of the dermatology department at Edinburgh University: “The data doesn’t support it. I think the sunburn issue is misleading.”

In the 1990s, leading medical researchers questioned whether there was a melanoma epidemic, or whether the apparent increase was more a product of increased surveillance and removal of “suspicious” moles that would previously have been left alone. Sam Shuster, who was professor of dermatology at Newcastle University at the time, argued that “melanomas are being invented, not found” as a result of “an ill-conceived propaganda exercise”. These critics met with such hostility from the medical authorities that few others have risked the charge of heresy. Instead, the discussion has been dominated by a skin cancer industry that has every interest in talking up the problem.

Rees was among those Nineties sceptics. He remains convinced that “there is little hard evidence to support these public health campaigns in the UK”.

Malignant melanoma remains a relatively rare condition in the UK, killing 856 men in 2001, a rate of 30 per million of the population, compared to a rate of 712 per million for lung cancer. It ranked 17th in the UK men’s cancer league table, just below mesothelioma (cancer of the chest lining) and multiple myeloma (cancer of the plasma cells in the bone marrow). But there are no shrill public campaigns around those conditions.

“If you’ve got a malignant melanoma,” Rees says, “it’s a big problem. But for society, it is not that big a problem. Most of us can only cope with worrying about so many things at once. Is this really the risk we want people focusing their attention on?” He sees the dramatic data on the epidemic of melanoma as “very suspicious”. “One of the best epidemiologists in Australia discovered that in New South Wales recorded rates had gone up by 40 per cent in a year. Well, cancer rates do not go up by 40 per cent. And the mortality rate has not increased.”

Rees does not deny a link between the sun’s UV rays and skin cancer. “There are two key determinants of skin cancer: skin colour and ambient UV radiation,” he says. “If your skin is jet black, it does not matter where you live. If you are pale-skinned, it does. It is not just a question of exposure to UV; what’s important is the particular pattern of exposure, and the different susceptibility of different people.

“If you look at the extremes, it’s clear. If we all lived underground in caves there would be fewer skin cancers, and if we all moved to Brisbane there would be more. But in the middle, where most of us live, the picture is far less clear. And it is uncertain, even if you could alter people’s behaviour in the way some would like, to what degree that would alter cancer rates. It is one thing to work out the cause, but trying to engineer a solution is much harder.”

The link between an episode of severe sunburn and cancer doesn’t stand up, Rees says. “This has been used as an example of what is called recall bias. In the US they followed half a million nurses from age 17. Some of them got a melanoma, and when they asked these people ‘did you ever get sunburn?’, of course they said yes. But when they went back and looked at what these nurses had said before they got it, there was virtually no association with sunburn.”

So what is a sensible attitude for pasty Brits to take to the sun, sun protection and skin cancer?