Redheads may have more to worry about than sun exposure when it comes to melanoma as research suggests a risk of the skin cancer independent of harmful ultraviolet rays.
Red-haired and fair-skinned people have long been considered at most risk of the sun's damaging effects because they are prone to sunburn, but recent research has explored whether certain skin pigments can lead to melanoma without UV rays.
In a newly-published study, US researchers used mice genetically similar to humans and which were red hair and fair-skinned, or with dark skin or albino colours. They found more cases of melanoma in red-headed mice than in the other two types, because of mechanisms independent of UV light.
"We were particularly interested in understanding the mechanisms underlying melanoma formation in the context of the fair skin genetic background," study leader and cancer biologist David Fisher told science journal Nature.
"There is something about the redhead genetic background that is behaving in a carcinogenic fashion. It means that shielding from UV would not be enough."
At the centre of the research was pheomelanin, a form of the skin pigment melanin typically produced by people with red hair.
The red-yellow pheomelanin was less effective at protecting skin from UV damage than eumelanin, found in people with darker hair.
The difference between the two was caused by a mutation in the gene MC1R.
Dr Fisher told the journal he and his team were left "shocked" when half of the ginger mice had developed melanoma before the scientists could expose them to UV light to monitor differences in melanoma development.
It suggested that the pigment was a cause of melanoma, and that risk could be related to the pigment-production process in melanin-containing cells called melanocytes.
The effect was not seen in the pigment-free albino mice.
The team concluded that although protection from UV radiation was important, additional strategies could be needed for optimal melanoma prevention.
Tauranga-based dermatologist Paul Salmon said medical professionals had for years questioned how melanoma could develop independently of UV rays.
"But we do know that UV radiation is obviously by far the biggest influencing factor in whether you end up with melanoma or not - there's no doubt about that."
Cancer Society of New Zealand skin cancer control promotions adviser Barb Hegan said said people needed to be sun-smart no matter what their hair colour.
The findings
* People typically with red hair and fair skin produce pheomelanin, a chemically different type of the skin pigment melanin than eumelanin, found in those with darker hair.
* Pheomelanin is less effective at protecting skin from damage from UV rays than eumelanin. The difference in the two is caused by a mutation in the gene MC1R.
* But a new study suggested the pigment itself was a cause of melanoma, and that risk could be related to the pigment-production process in melanin-containing cells called melanocytes.
Melanoma in NZ
* New Zealand and Australia have the highest melanoma incidence rates in the world.
* Melanoma is the fourth most common cancer in New Zealand, with more than 2000 cases per year.
* In 2008, 317 people died from melanoma in New Zealand - 202 men and 115 women.
Melanoma Foundation of NZ