Redheads sunburn easily, but that may not be the only reason they are at high risk of skin cancer. New research suggests the pigment that colors their skin may set them up for cancer-spurring sun damage even if they do not burn.

More than 1 million Americans develop some form of skin cancer each year. Among those most at risk are people with light skin, hair and eyes, a combination frequent in redheads. They are particularly prone to sunburns, a risk factor for anyone, especially if the burns occur in childhood.

Scientists long have wondered if something else plays a role in redheads' high risk. One theory focuses on melanin (search), the skin pigment that darkens with sun exposure to provide either a tan or freckles. People with red hair have a chemically different type of melanin than people with dark hair.

Duke University (search) researchers on Sunday reported the first direct evidence that those melanin differences indeed may be a culprit. It turns out that redheads' melanin is more vulnerable to a type of DNA-damaging stress from the sun's ultraviolet rays.

To study the question, Duke chemistry professor John Simon (search) turned to hair. It is very difficult to cull melanin from human skin, but the pigment is the same in hair. He bought naturally red and black hair from wig makers and, for a broader sample, offered to pay for red-haired Duke students' haircuts in return for the clippings.

Using a special laser and microscope, Simon analyzed how the pigments reacted as they absorbed either ultraviolet B rays (search) associated with sunburn, or ultraviolet A rays (search), which can penetrate and damage skin even without a burn.

Both UVA and UVB light caused a photochemical reaction with the redheads' pigment, called pheomelanin. The reaction creates oxidative stress, where oxygen molecules called free radicals are formed that damage DNA and cells in ways that, over time, can accumulate to spur cancer.

In contrast, only UVB light caused that oxidative reaction with the pigment from black hair, called eumelanin, Simon reported.

His research, funded by the government and Duke, was presented at a meeting of the American Chemical Society (search).

"There has been speculation for years that pheomelanin could be a key pathway" in skin cancer formation, said Dr. Martin Weinstock of Brown University, a spokesman for the American Cancer Society (search). "The thought is that eumelanin does a reasonable job of protecting against UV and pheomelanin might in fact aggravate damage."

While more research is needed, Simon said in an interview that his study reinforces some practical advice: Slather on sunscreen that promises to protect against both UVA and UVB rays.

All sunscreens work against UVB, but it can be hard to tell how much UVA protection "broad-spectrum" ones offer. The Food and Drug Administration is working on long-delayed labeling guidelines that promise to one day help consumers figure that out.

And what about blondes? They harbor some of the same pigment as redheads, Simon said.