A study of twins has confirmed the link between having moles and the increased chance of developing skin cancer.
Researchers from the Department of Twin Research at King's College London looked at the genetic codes of more than 1,500 adult female twins in the UK.
The study, published in the journal Nature Genetics, found that two genes which regulate the appearance of moles can double the risk of melanoma.
Scientists discovered that single-letter variations in the code associated with high mole counts were found in two genes linked to the cancer. Having two copies of the same two genes can double the chances of developing melanoma.
Professor Tim Spector, who heads the twins research team, said: "These novel genes regulating moles can lead to a doubling in melanoma risk.
"Twins have helped us over the last 13 years to find that moles are heritable and then isolating the gene regions, and now the actual genes involved."
It was already known that having a lot of moles is a major risk factor for the disease. Previous research from King's College had shown that genes influencing numbers of moles might overlap with those for melanoma.