Research on identical twins could pave the way for new treatments for skin cancer.

The study, carried out at St Thomas' Hospital, London, suggests that a tendency to develop the potentially fatal form of skin cancer known as melanoma may be inherited.

Until, it has been thought that melanoma, characterised by a dark, uneven mole on the skin, was in part caused by over-exposure to solar radiation.

However, the study, at the hospital's twin research unit, found that identical twins were more likely to have a similar number of moles than twins who are not identical.

The researchers were surprised to find that the degree of similarity in the number of moles increased with age - even when the subjects were exposed to different environmental factors.

The researchers studied 450 pairs of twins, of which 127 were identical.

They counted the number of moles and measured the amount of freckles they had on a scale of 0 to 100.

Once the identical twins reached the age of 50, there was an increased similarity in the number of pairs of individual moles.

It was estimated that 84% of moles that appear after this age are inherited.

The researchers suggest that once people reach a certain age some genes become more active, and this may trigger a susceptibility to skin cancer.

Dr Veronique Bataille, honorary consultant dermatologist at the Twin Research Unit, study said: "The study has shown that genetic factors are important in the number of moles you have as an adult and these genetic factors become more important as people get older.

"Sun exposure still has a part to play as it may also affect the way genes work in producing moles."

Dr Tim Spector, director of the Twin Research Unit, said: "More research needs to be done with larger numbers of twins but proving that moles are gene related is a crucial step towards uncovering genes important in skin cancer, which may lead to earlier diagnosis and new treatments."

Professor Rona Mackie, an expert in skin cancer from the University of Glasgow, said it was important that people with a family history of melanoma did not panic.

She said only 5% of people with melanoma had been shown to have a family history of the disease.

She said: "You do not inherit melanoma, you inherit a tendency to develop the disease.

"The advice remains the same: be careful about over-exposure to the sun, do not get sunburned, know your moles and show any new or changed pigmented lesion to your doctor."

Malignant melanoma is the least common, but most aggressive form of skin cancer.

Early treatment is vital as it accounts for the vast majority of deaths from skin cancer.