Natural red hair occurs in approximately 1–2% of the global population, making it the rarest natural hair color.
Genetic Basis
- Autosomal recessive variants in MC1R (melanocortin 1 receptor) on chromosome 16.
- Loss‑of‑function variants → ↓ eumelanin (brown/black), ↑ pheomelanin (red/yellow).
- Highest frequency in Celtic populations (Scotland ~13%, Ireland ~10%).
Associated Traits
- Fair skin, freckling, UV sensitivity (↑ melanoma risk).
- Altered pain perception (↑ thermal pain threshold, ↓ opioid efficacy).
- Vitamin D synthesis efficiency in low UV environments (evolutionary advantage at high latitudes).
Demographic Note
Absolute numbers are declining due to global population mixing, but the allele persists. Red hair remains a striking example of recent human evolutionary adaptation.
