A study of hundreds of women has revealed that those who avoided the sun's rays looked up to 20 years younger than they actually are.

However, other supposed rules for a youthful complexion, from drinking lots of water to sleeping well and exercising regularly, failed to hold back the hands of time.

Only keeping out of the sun, and wearing sunscreen when this wasn't possible, made a difference, the American Academy of Dermatology's annual conference will hear today.

The intriguing finding comes from a study of 231 women of all ages who were quizzed about their lives, including whether they were sun-worshippers.

When researchers from Massachusetts General Hospital in the US - commissioned by skincare firm Olay - guessed how old the women were, they found those who took care in the sun tended to have aged more slowly.

A lucky four had so few wrinkles and age spots, and such a glowing complexion, that they appeared to be a full two decades younger than they really were.