Tiny chemical differences in how our skin reacts to ultraviolet light could explain why redheads are more likely to suffer skin cancer, say US scientists.
Redheads should take extra care to avoid sunburn
The answer lies in the skin and hair pigment melanin, the team from Duke University, North Carolina, believe.
People with ginger hair have pigment that is chemically different from that of people with darker hair, they found.
This difference might explain why people with red hair burn easily and are prone to sun damage.
Professor John Simon from Duke University will present the findings at the 230th national meeting of the American Chemical Society in Washington DC at the end of August.
His team, along with colleagues from at the Funjita Health University in Japan, used a special microscope and an ultraviolet (UV) laser to see what was happening to the pigment-containing structures in hair, called melanosomes, from redheads and black-haired people.
They measured something called the oxidation potential of the red and black melanosomes.
This is how likely chemicals are to activate oxygen by taking up electrons.
Such changes are known to be linked to cell damage and cancer.
They found that the red melanosomes were much more reactive than the black melanosomes.
This would suggest that it takes less of a trigger, namely UV rays in sunlight, to make potentially harmful cellular changes in people with red hair.
Professor Simon explained: "Activating oxygen can produce compounds called radicals that put oxidative stress on cells. Such stress could ultimately lead to cancer and other diseases."
He said his work "links the red pigments to possible oxidative stress through their electrochemical properties."
Dr Steven Rotter, dermatologist and spokesman for the US Skin Cancer Foundation, said: "This helps to clarify at a molecular level something we have known for years.
"We know that people with red hair are less protected inately because of the pigment in their skin but we had not know exactly why."
He said that not only did people with red hair have less protective pigment than people with darker hair, but the pigment they did have appeared to be more likely to react to produce harmful agents associated with cancer.
Ed Yong, science information officer for Cancer Research UK, said: "It is well known that red or fair-haired people have a higher risk of skin cancer, and this study provides us with a possible explanation for this."
He advised people with red hair and fair skin to take particular care to avoid sunburn and to protect their skin by avoiding the sun in the middle of the day, seeking shade and covering up with a T-shirt and sunglasses and using sunscreen of at least factor 15.