A gene variant carried by people with red hair, pale skin and freckles may boost skin cancer risk even without exposure to the Sun's rays, researchers said Tuesday.
The risk, rather surprisingly, is also higher for people who possess the genetic DNA signature but not the tell-tale physical traits, reported the international team.
The findings, published in the journal Nature Communications, are based on a genetic analysis of skin cancer tumours from more than 400 people.
Read: Suspicious pigment spots more common on darker skin
It revealed that tumours from people with a redhead variant of the MC1R gene had 42 percent more mutations – the equivalent of 21 years of additional sun exposure in people without it.
Though most gene mutations are innocuous, the more that occur, the more likely a normal human cell will be to change into a cancer cell.
The findings suggested that people with an MC1R variant are more susceptible to mutagenic processes, such as UV exposure for example, that can trigger skin cancer, known as melanoma.
"This work is significant because its conclusions apply to a high proportion of the population, those people that carry at least one copy with a genetic variant in MC1R," study co-author David Adams of the Wellcome Trust Sanger Institute told AFP.
Read: Blue-eyed people may face higher melanoma risk
In some countries, such as England and Ireland, this could be as much as a third of the population – though only about one or two percent of all people have red hair.
Many of those at risk will not even know that they carry the variant, said the researchers.
Redheads burn more easily
Redheads receive one copy of the gene variant from each of their parents. But people who get a copy from their father or mother alone, will probably not have ginger hair – and may remain oblivious of their particular genetic makeup.
It has long been known that redheads burn more easily in the sun and are more susceptible to the mutagenic effects of UV light – thus also at higher risk of skin cancer.
But the new study suggests there are more ways, "possibly UV-independent" in which MC1R variants can increase the risk of melanoma, said Adams.
Read: Can orange juice raise your melanoma risk?
It also revealed for the first time, the risk to non-redhead carriers of the gene variant.
"These people should exercise extra care when going out in the sun as they might be highly susceptible to UV radiation and other mutagenic mechanisms, something that many people carrying MC1R genetic variants don't realise," said Adams.
People with red-haired relatives have a higher chance of carrying an MC1R variant, and should take extra care, said the team.
It was not clear whether the mutations mean that melanoma in redheads is more or less severe.
What is skin cancer?
Symptoms of skin cancer
Types of skin cancer