Melanin filters out UV radiation, but the melanin in hair follicles, particularly in light hair, actually increases the sun damaging effects of UV rays and causes cell death in the hair follicle, said Douglas Brash, principal investigator and professor of therapeutic radiology, genetics and dermatology at Yale School of Medicine.
Brash said he had been curious why people with dark hair and fair skin were not as vulnerable to skin cancer as fair skinned blondes and redheads. "I wondered if it was related to the melanin," he said.
Brash's laboratory used mice engineered with pigmentation for yellow or black hair, as well as albino mice with no pigment at all. The researchers then irradiated the mice with UV rays that are about the same as what breaks through the ozone layer, affecting humans.
The cell death was concentrated around the hair follicles, which are the only location of melanin in mice. Dying cells were particularly pronounced in the yellow-haired mice and was absent in albinos.
"What this tells us is that melanin is not only good for you, it also can be bad. It depends on the color of your particular melanin," Brash said. "Even red melanin can vary widely, depending on whether your ancestors were Irish, Swedish or Dutch, and some of these variations are known to be associated with greater risk for skin cancer."