Red hair is a striking feature, but curiosity often arises regarding the color of hair elsewhere on the body. Many people notice that hair on a redhead’s arms, legs, and eyebrows often appears significantly lighter, blonde, or even colorless. This observation leads to the question of whether the genetic trait responsible for red hair results in a uniform distribution of that color across every single hair follicle. The answer lies within the genetic code that controls human pigmentation.
The Genetics Behind Red Hair
The distinctive red hue is caused by a gene variant known as the Melanocortin 1 Receptor, or MC1R, located on chromosome 16. This gene provides instructions for making a receptor that plays a major role in determining the type of melanin produced by pigment-making cells called melanocytes. The MC1R receptor typically signals melanocytes to produce eumelanin, which is the dark brown or black pigment found in people with darker hair colors.
However, in redheads, the MC1R gene has a non-functional variant. This functional impairment means the melanocyte is unable to properly respond to the signal to produce eumelanin. Instead, it defaults to producing high levels of pheomelanin, a reddish-yellow pigment. The dominance of this pheomelanin over the suppressed eumelanin gives hair its copper, auburn, or ginger shade.
Why Body Hair Color Varies
A person with red hair on their head may have different colored body hair because the expression of the MC1R gene is not uniform across all hair follicles. The body possesses different types of hair, most notably terminal hair on the scalp and vellus hair on the body. The genetics controlling pigment production are regulated independently in these separate regions, meaning hair on the legs, arms, and chest may express the MC1R mutation differently than the follicles on the scalp.
Since red hair is characterized by low eumelanin, the body hair often appears lighter because it lacks both the dark pigment and a strong concentration of pheomelanin. If the hair follicle produces very little of either melanin type, the resulting vellus hair will be fine, translucent, and appear blonde or virtually colorless. This localized balance of the two melanin pigments varies from one follicle population to the next, explaining why a redhead may have bright red scalp hair but nearly blonde eyebrows or light chest hair.
Other Unique Traits of Redheads
The MC1R gene variant affects more than just hair color; it also influences several other physical and biological characteristics. The genetic change that causes red hair also leads to reduced eumelanin production in the skin, resulting in fair skin that is highly sensitive to ultraviolet light. This reduced pigment protection explains the high prevalence of freckles and the difficulty many redheads have with tanning.
The MC1R gene also has a role in the body’s pain perception system. Studies have shown that the mutation may alter how the central nervous system processes pain signals, leading to differences in sensitivity. Redheads may be more sensitive to certain types of pain, such as thermal pain from heat or cold. Anesthesia requirements are also impacted, as red-haired individuals often need higher doses of local anesthetics to achieve the same level of sedation. They have also been found to respond more effectively to opioid pain medications.