Hair Colour

Hair colour is determined by melanin pigments within the cortex: eumelanin (brown/black) and pheomelanin (red/yellow). Their ratio, density, and distribution create the visible shade.

Biology

  • Melanocytes in the follicle bulb transfer melanin into growing hair.
  • Greying (achromotrichia) reflects reduced pigment production with age and oxidative stress.
  • Genetic variations in the MC1R gene can lead to red or auburn hair.
  • UV radiation can alter pigmentation, increasing eumelanin production in some cases.

Colour chemistry & practical notes:

  • Permanent oxidative dyes use ammonia (or alternatives) and hydrogen peroxide to open the cuticle and either remove natural melanin (lightening) or deposit oxidation products in the cortex; this process increases porosity and weakens the fibre if repeated.
  • Semi‑permanent dyes deposit pigment on or near the cuticle and do not require peroxide; they fade over weeks and are less damaging.
  • Bleaching (high‑concentration peroxide) removes melanin entirely and is the most structurally damaging process; reconstructive treatments and careful timing reduce cumulative harm.

Practical detail: bleaching is performed with peroxide developers (commonly 10–40 volume / ~3–12% H2O2) often combined with persulfates and alkaline agents to accelerate lift. Aftercare includes toning to neutralise warm undertones, purple conditioners/shampoos, and regular moisture/protein treatments. For an expanded guide see Hair Bleaching.

  • Hair porosity influences dye uptake: highly porous hair takes dye more readily (use lower developer strength), low‑porosity hair may require more aggressive preparation.

Care after colouring:

  • Use colour‑safe, low‑sulphate cleansers, regular conditioning, and UV protection to slow fading.
  • Bond‑rebuilding salon treatments (e.g. formulations that claim to restore disulphide bonds) can improve manageability after chemical processes but do not fully return fibres to their pre‑bleach strength.

Pigment Types

  • Eumelanin: Responsible for black and brown shades. Higher concentrations result in darker hair.
  • Pheomelanin: Produces red and yellow tones. Found in higher amounts in red and blond hair.

Notes on red hair

  • See Red Hair for a dedicated discussion of pheomelanin‑rich hair, MC1R genetics, health implications (UV sensitivity, skin cancer risk) and practical care notes for preserving red tones.

Natural Hair Colours

Hair colours range from black, brown, blond, and red to grey and white. The Fischer–Saller scale categorizes these shades:

  • Black: High eumelanin content, common in populations near the equator.
  • Brown: Medium eumelanin levels, with variations like chestnut and auburn.
  • Blond: Low melanin levels, often found in Northern Europeans.
  • Red: High pheomelanin content, rarest globally, most common in the British Isles.
  • Grey/White: Caused by a lack of melanin, often due to aging or stress.

Care & Styling

  • Permanent dyes and bleach work by opening the cuticle and altering cortex pigment; they increase porosity and can weaken fibres.
  • Semi‑permanent dyes and glosses coat or slightly penetrate the cuticle with less damage.
  • UV protection and hydration are essential for maintaining vibrant colour.

Writing Tips

  • Use colour to signal mood or identity shifts (a copper rinse after a breakup, the first silver strands embraced).
  • Pair colour with texture and movement for vivid imagery: “inky coils,” “sun‑caught chestnut,” “storm‑silver waves.”
  • Highlight cultural or genetic significance of hair colour in character development.

Example

"Under the platform lights her curls flashed auburn—amber at the tips, darker at the roots where new stories were growing."

See also