A new study has revealed why redheads should be wary of staying out of the sun if they want to avoid developing melanoma, a deadly form of skin cancer.

Genes that give a person red hair, pale skin and freckles heighten their odds of developing skin cancer, and the risk is equivalent to having 21 additional years of being exposed to the sun.

In the study, which was published in Nature Communications on July 12, researchers have found that gene variants linked with red hair and freckled skin were associated with increased number of mutations that can lead to skin cancer.

Researchers looked at tumor DNA sequences gathered from more than 400 individuals and found that the tumors of those who carry the red hair gene variant have 42 percent more mutations associated with sun damage compared with those who do not have this DNA.

"This figure is comparable to the expected mutational burden associated with an additional 21 years of age," the researchers wrote in their study.

Redheads, who comprise between 1 and 2 percent of the global population, have two copies of a variant of the MC1R gene, which plays a role in melanin pigmentation and influences a person's likelihood to have red hair, pale skin and freckles. These variant increased their vulnerability to get sunburn.

Exposure to the harmful ultraviolet rays from the sun or sunbeds is known to cause DNA damage, and scientists believe that the type of skin pigment that redheads have allow more UV to penetrate the DNA.

"People with red hair have a different type of melanin than people who don't have red hair — and the type of melanin that redheads have is less able to protect them from the sun," explained study researcher David Adams, from the Wellcome Trust Sanger Institute.

Non-cancerous cells also appear to accumulate mutations in the tumor more readily in those who carry these MC1R variants. These mutations can contribute to cancer gaining foothold, drive its growth or prevent DNA-repair genes from correcting the problematic mutation.

The research likewise found that the MC1R gene variation does not only increase the number of mutations linked to sunlight. It also increases the level of non-sun linked mutations in the tumors. Tumors with more mutations are likely to become fatal.

Study researcher Julie Sharp, from the cancer Research UK, said that the research provides evidence why red-haired people and those who have fair skin, those who burn rather than tan or those who have moles and freckles should be careful to protect themselves from the strong sun.