What Determines Hair Color? Melanin, Genetics, and Aging

The Pigment System

Hair color comes from melanin produced by melanocytes in hair follicles. Two types:

• Eumelanin: Brown/black pigment. High concentration = black/dark brown. Low = blond.
• Pheomelanin: Red/yellow pigment. High concentration = red hair. Present in all hair but usually masked by eumelanin.

Genetic Control

• MC1R gene (chromosome 16): Primary regulator. Variants → red hair, fair skin, freckles.
• Multiple genes: HERC2, OCA2, TYR, TYRP1, SLC24A4, KITLG, others — polygenic inheritance.
• Ethnic patterns: East Asian/European variants differ. African populations: high eumelanin diversity.

Natural Color Spectrum

• Black: High eumelanin, dense granules
• Brown: Moderate eumelanin
• Blond: Low eumelanin, sparse granules
• Red: High pheomelanin, low eumelanin (MC1R variants)
• White/Gray: Melanocyte depletion (aging) or absence (albinism/poliosis)

Modifying Factors

• Age: Melanocyte stem cell exhaustion → graying (typically 30s-50s). Stress may accelerate.
• Sun: UV bleaches melanin → lighter tips (photomelanosis).
• Health: Thyroid, B12 deficiency, vitiligo, chemotherapy can alter pigment.
• Chemical: Dyes, bleaches, permanents alter artificially.

Structural Color

Some animals (birds, butterflies) use nanostructure, not pigment. Human hair is purely pigmentary.