Red hair is a natural genetic variation, making it one of the rarest hair colors globally, found in 1 to 2 percent of the world’s population. While relatively uncommon, red hair is most prevalent in individuals of Northern and Northwestern European ancestry. Its presence is determined by specific genetic factors.
The Genetic Blueprint of Red Hair
The science behind red hair centers on pigments called melanins, which determine hair, skin, and eye color. There are two types of melanin: eumelanin, which produces brown and black pigmentation, and pheomelanin, responsible for red and pink hues. Individuals with red hair have higher levels of pheomelanin and lower levels of eumelanin in their hair and skin.
This unique balance of pigments results from variations in the Melanocortin 1 Receptor (MC1R) gene. The MC1R gene provides instructions for a protein that plays a role in signaling the production of both eumelanin and pheomelanin. When the MC1R protein is activated, it leads to the production of eumelanin. However, certain genetic variants in the MC1R gene can lead to an altered or less functional receptor. This deactivation causes melanocytes, the cells that produce pigment, to produce more reddish pheomelanin instead of darker eumelanin, resulting in red hair.
Inheritance Patterns and Your Chances
The inheritance of red hair follows an autosomal recessive pattern. This means an individual needs to inherit two copies of the variant MC1R gene—one from each parent—to express the red hair trait. If a person inherits only one copy of the variant gene, they will likely not have red hair, but they become a “carrier” and can pass the gene to their offspring.
This recessive inheritance explains how parents who do not have red hair can still have a red-haired child. If both parents are carriers of the MC1R gene variant, even if they have darker hair colors, there is a 25% chance their child will inherit two copies of the variant and thus be born with red hair. If one parent has red hair and the other is a carrier, there is a 50% chance their child will have red hair. When both parents have red hair, their children are almost certain to have red hair because they will inherit two copies of the variant gene.
Unique Traits Linked to Red Hair
Red hair is accompanied by other physical characteristics, largely due to the same genetic variations in the MC1R gene. Fair skin and freckles are associated with red hair because the altered MC1R function also reduces the production of eumelanin in the skin, leading to lighter pigmentation and a reduced ability to tan. This lighter skin also results in increased sensitivity to ultraviolet (UV) light, making redheads more susceptible to sunburn.
Beyond skin and freckles, there are other associations. Research suggests that individuals with red hair may have different pain sensitivities. Some studies indicate a higher pain tolerance for certain stimuli, while others suggest increased sensitivity to thermal pain or a need for higher doses of some anesthetics. Additionally, redheads may be more efficient at synthesizing Vitamin D under lower light conditions, possibly an evolutionary adaptation for populations in northern climates where sunlight is less intense.