Winter is the time for topping up faded tans. But taking to a sunbed can be even riskier than sunbathing, warns Janet Fricker
Monda Bell has large blue eyes, white-blond hair and a broad Tennessee accent. From a small town near Memphis, she is proud of her good looks and slim figure. Yet the skin on her back, arms and legs could belong to a woman in her fifties rather than a 33-year-old secretary. It has suffered the effects of photoageing - skin damage caused by sunlight.

Monda was, by her own admission, a sunbed freak. For eight years, she regularly used a tanning bed before going on holiday to Florida with her husband. With her fair skin, she knew she would burn easily and felt she needed to take precautions. "I would use the sunbed once or twice a week for a couple of months to get a base tan so that I wouldn't burn when I got there," she recalls.

An ageing skin is the least of her problems: Monda has had more than 19 operations to remove skin cancers from her back, face, stomach and legs. Her skin is so disfigured by surgery that she never leaves the house without make-up. She attributes her problems to the damaging effects of the tanning beds.

Now is the time that many people think of using a sunbed to "touch up" their summer tan and boost morale in the dark days of winter. But despite the "feel-good" effect of a tanned skin, dermatologists fear that a tan is a sign that skin damage has already occurred. Doctors are seeing more and more cases of photoageing in young people who use sunbeds regularly.

"I have patients of 35 who use sunbeds with skin characteristics normally seen in women of 60," says Professor Rex Amonette, clinical professor of Dermatology at the University of Tennessee, Memphis. "Their skin is beginning to sag; it appears loose with considerable freckling and many more wrinkles than you'd expect."

Monda is one of many people labouring under the misconception that acquiring a "base tan" before going on holiday will protect them from the sun's rays. But it was probably Monda's "base tan" that contributed to her skin damage. New evidence suggests that even a mild tan is the skin's response to overdoses of ultraviolet (UV) radiation.

Professor Barbara Gilchrest of the Boston University Medical School attached small fragments of DNA to the shaved backs of guinea pigs. This mimics the repair process that occurs after UV exposure where the damaged DNA is excised by certain enzymes. Within a few days the animals developed a tan.

"Our work implies that tanning arises through DNA damage," says Professor Gilchrest. "It seems that DNA fragments trigger certain enzymes which induce the production of the pigment melanin."

Melanin is a complex molecule that absorbs UV radiation, giving rise to the brownish colour of a tan. It is estimated to provide sun protection comparable to an SPF of 2 to 4. "But the initial DNA damage outweighs any of these protective effects," says Professor Gilchrest.

The problem is that by producing mutations in the DNA, UV light may damage proteins that regulate cell division and repair, leading to abnormal cell growth, which may ultimately cause tumours and skin cancers. In practical terms, Professor Gilchrest's findings imply that even a gentle tan is dangerous.

Doctors in the US and Britain are noticing a disturbing trend of skin cancer in young patients. This year, the Department of Health, the British Medical Association and the Academy of Dermatology issued warnings against the use of tanning beds. Evidence is mounting that the risks include skin cancers, premature ageing, dry skin, cataracts and damage to the immune system. In an article in the American Academy of Dermatology Journal, Professor Amonette, the academy's president, concludes: "Given the risks, the use of tanning beds for cosmetic purposes cannot be recommended."

For Monda, the first sign that something was wrong came three years ago when she noticed anitchy patch on her back. Her doctor thought she had eczema but when the condition persisted he referred her to Professor Amonette, who diagnosed a basal cell carcinoma. This was the start of a catalogue of operations.

"I get depressed because whenever I go back for check-ups, they seem to find more cancers," she says. So far, the doctors have found only squamous and basal cell carcinoma, but there's always the fear that they might find a malignant melanoma. She was very distressed by the four operations on her face, one of which involved cutting off an eyebrow and stitching it back on again. The surgery has left scars and there have been other costs: "When I came home after having a cancer cut off my face, my seven-year-old son Bradley was so frightened that he wouldn't come into the room," she says.

Studies have yet to quantify the number of cases of cancer directly caused by sunbeds. But Professor Amonette has already seen more than 30 young patients with skin cancers he relates directly to their use. He believes that since the beds have only been used for the past 10 to 15 years, we are only seeing the "tip of the iceberg".

Dermatologists fear that indoor tanning lamps may prove even more damaging to the skin than natural sunlight. The difference is that indoor tanning relies primarily on UVA radiation, while an outdoor tan relies primarily on UVB radiation. Researchers are only beginning to unravel the biological differences between UVA and UVB, but evidence suggests that UVA, the longer wavelength radiation, penetrates into the deeper layers of the skin, getting through to the dermis. This may have a more detrimental effect.

A study by Dr Robert Lavker, of the University of Pennsylvania in Philadelphia, found that people exposed to repeated low UVA doses showed greater skin damage than those receiving comparable doses of sunlight. Skin biopsies showed the UVA subjects had a greater inflammatory response in the dermis, and that their elastin fibres had greater deposits of lysozyme, an enzyme linked to sun damage.

Despite mounting evidence against the use of sunbeds, many people remain reluctant to give them up. Even Professor Amonette understands the attraction. "A real euphoria accompanies tanning beds. They're warm, comforting and produce the same effects as light therapy in seasonal affective disorder."

Although familiar with her ordeal, many of Monda's friends are undeterred. One has already had a skin cancer excised, but still goes to a tanning salon.

"A tan makes her feel happy," says Monda, "and she'd rather live for the present than worry about the future."