Despite the huge resources invested in researching the "fountain of youth", most anti-ageing remedies are little better than expensive moisturisers, Chris Griffiths, professor of dermatology at the University of Manchester, said.
The exceptions are sunscreens with a protection factor of over 15, which not only protect but help to reverse the damage caused by the sun, and creams containing retinoic acid, the treatment developed for acne, which has been shown to fill out a blotched and wrinkled skin.
Professor Griffiths told a conference on ageing and image in London yesterday that the most effective measures to prevent premature wrinkles were to give up smoking and cover up in the sun.
Natural or "intrinsic" ageing, determined by a person's genetic inheritance and chronological age, shows itself in a skin that is smooth, unblemished and only finely wrinkled. It is seen at its purest in people who spend their lives permanently and completely protected from the sun.
The effects of natural ageing, which vary from person to person, are aggravated by environmental effects - "extrinsic ageing" - including sun exposure (photo-ageing), smoking and, possibly, a high- fat diet.
These leave the skin with extra melanin, the pigment that turns it brown, and less collagen, the substance that gives the skin its strength and elasticity. By contrast, natural ageing reduces rather than increases the level of melanin and causes only a slight loss of collagen.
Professor Griffiths said: "In the skin, natural ageing doesn't manifest itself until you are really very old. Most of the problems to do with appearance are due to photo-ageing. So if you can avoid sun exposure you can keep your skin in pretty good shape."
Microscopic examination of the skin showed it had the capacity to repair itself after sun damage - provided it was not subjected to further assault from the sun. Using a high- factor sunscreen could therefore create circumstances in which the natural process of repair could begin."The message is that it is never too late to use a sunscreen," he said.
The discovery that retinoic acid could help to repair skin damage was made accidentally more than a decade ago. Middle-aged women using the cream to treat late onset acne found it also reduced their wrinkles. Studies have since shown it stimulates collagen production, which is severely reduced in sun-exposed skin, and blocks enzymes that break down collagen.
Retinoic acid is only available on prescription, although a number of anti-ageing creams contain retinol (vitamin A), which is broken down on the skin to retinoic acid, but in a much lower concentration.
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The Secrets Of Youth
t Choose your parents carefully - genes influence how rapidly you age
t Stay out of the sun, wear a hat or use a high-factor sunscreen
t Don't smoke
t Avoid animal fats and eat plenty of fruit and vegetables (skin-damaging free radicals in the fats are mopped up by anti-oxidants in the fruit)
t Use a basic moisturiser
t Drink red wine (although unproven, its anti-oxidant properties may help to neutralise damaging free radicals)
t Use a cream containing retinoic acid (only available on prescription) or the less effective retinol (available over the counter).