Outbreak of moles on right arm indicates a high risk of cancer
Having more than 11 moles on their right arm could mean a person has a higher risk of skin cancer, according to research.
Experts believe that the number of moles someone has on their right arm is the best indicator of how many moles they have altogether - and having more than 100 moles on the body is thought to be a "strong predictor" of a higher risk of melanoma.
People with more than seven on their right arm had nine times the risk of having more than 50 in total, while those with more than 11 were more likely to have more than 100 on their whole body.
Researchers at King's College London concluded that counting moles in a "proxy" body area such as the arm was a good marker of potential problems.
The study, funded by the Wellcome Trust, examined data from 3,594 female twins.
Nurses from St Thomas' Hospital, London counted moles on 17 body areas and recorded skin type, hair and eye colour and freckles, with results checked against a further study.
The area above the right elbow was particularly predictive of mole totals. Legs, too, were strongly linked with the final figure, while men's backs also highlighted a higher risk.
Dr Simone Ribero, the lead author, said the study would help GPs.
"The findings could have a significant impact for primary care, allowing GPs to more accurately estimate the total number of moles in a patient extremely quickly.
"This would mean that more patients at risk of melanoma can be identified."
People with white skin average about 30 moles, although some have up to 400.
The reason for the differences is unknown, as is the function of moles.
Previous research has shown that up to 60pc of an average person's susceptibility to moles is inherited.
Dr Claire Knight, health information manager at Cancer Research UK, said the study "could be helpful because we know that people with lots of moles have a higher risk of melanoma."
Other risk factors for melanoma include having red or fair hair, fair skin, light-coloured eyes or sunburn.
"But less than half of melanomas develop from existing moles. So it's important to know what's normal for your skin and to tell your doctor about any change in the size, shape, colour or feel of a mole or a normal patch of skin.
"Melanoma can develop anywhere on the body. It is most common on the trunk in men and the legs in women," said Dr Knight.
Malignant melanoma is the fifth-most common cancer in the UK; more than 2,000 people die from it per year.
The study has been published in the 'British Journal of Dermatology'.