Bad news for fair-skinned red-heads: wearing a hat and sunblock and sitting in the shade won't necessarily protect you from skin cancer. Studies in animals suggest the risk remains regardless of exposure to ultraviolet light.

David Fisher at Massachusetts General Hospital in Boston and colleagues introduced a gene linked with melanoma - the most dangerous form of skin cancer - into mice engineered to be albino, or to have either red or black hair.

The team had planned to study the incidence of melanoma after exposure to UV light - known to be particularly damaging to the fair skin that often accompanies red hair. But before they could start, the red-haired mice developed tumors.

"It was a big surprise," says Fisher.

To test whether it was the MC1R gene, which gives both mice and humans red hair, or the red pigment itself that was involved, the team created albino-red hair hybrids: mice with an MC1R gene but whose hair was white. Hybrid mice were protected from melanoma, says Fisher, indicating the pigment itself plays a role.

"Red pigment has a capacity to cause oxidative stress," he says, which might lead to genetic mutations (Nature). Discovering the mechanisms involved may lead to protective strategies that go beyond shielding the skin from UV, Fisher adds.