The Biology of Hair Color
Hair color emerges from specialized cells called melanocytes within hair follicles. These cells produce pigments known as melanin, which determine the specific shade of hair based on their type and amount.
There are two primary types of melanin: eumelanin and pheomelanin. Eumelanin is responsible for black and brown shades, with higher concentrations leading to darker hair. Pheomelanin contributes to red and yellow tones.
The ratio and quantity of these two pigments determine a person’s natural hair color. For example, high levels of eumelanin result in black or dark brown hair. A balance of eumelanin and pheomelanin can lead to lighter brown or blonde hair, while red hair results from a higher proportion of pheomelanin and lower levels of eumelanin.
The Genetic Basis
Hair color is largely determined by an individual’s genetic makeup, with multiple genes influencing the final shade. The Melanocortin 1 Receptor gene (MC1R) is one of the most significant genes involved, playing a central role in regulating the balance between eumelanin and pheomelanin production.
Variations or changes within the MC1R gene can alter how melanocytes function. Certain MC1R variants are less effective at converting pheomelanin into eumelanin, leading to an accumulation of pheomelanin.
Inheriting two copies of a specific MC1R variant correlates with red hair. However, genetic expression is not always straightforward, as other genes can interact with MC1R, modifying the final hair color.
Explaining Regional Variations
Having brown hair but a red beard illustrates how genetic instructions are expressed differently across the body. While the MC1R gene may carry a red-associated variant, its influence is not uniform across all hair follicles.
Each hair follicle contains genes that can be activated to varying degrees. The MC1R gene, even with its “red” variant, may be expressed more prominently in facial hair follicles compared to those on the scalp.
Consequently, melanocytes in the beard might produce a higher proportion of pheomelanin. This localized difference in gene expression leads to the red color.
Although the differential expression of the MC1R gene is the primary explanation, other factors play minor roles, such as hormonal influences that could subtly impact pigment production in specific areas like the beard. Ultimately, the core reason lies in localized genetic instructions that govern melanin synthesis in different hair follicles across the body.