Receptor · Melanocortin 1 receptor

MC1R — the pigment switch

The receptor on melanocytes that decides between protective brown-black eumelanin and reddish pheomelanin. Its weak variants explain red hair and fair skin — and carry an independent melanoma risk.

By melanocortin.com editorialLast updated 2026

Pigment is the system made visible — the one receptor that turns a hormone into a shield, and the colour of a person into an act of protection.

Tissue
Melanocytes (skin & hair); immune cells
Key ligands
α-MSH, ACTH (agonists); agouti signalling protein (antagonist)
Signalling
Gs → cAMP → PKA, driving the pigment regulator MITF toward eumelanin
Accessory protein
None obligatory
Gene
16q24.3
Function
Switches melanocytes from red/yellow pheomelanin toward brown/black eumelanin — the master control of pigmentation and UV response.
When it fails
Loss-of-function variants drive red hair, fair skin, and raised melanoma risk.

MC1R is the melanocortin system's contribution to how you look — and to how well your skin defends itself against the sun. Sitting on the surface of melanocytes, it is the master switch that sets which kind of melanin those cells produce.[1]

The pigment switch

Melanocytes can make two broad classes of pigment: eumelanin, the brown-black pigment that absorbs UV and protects DNA, andpheomelanin, a reddish-yellow pigment that is a poor sunscreen and can itself generate damaging free radicals. When α-MSH (or ACTH) activates MC1R, the receptor — coupled to Gs — raises cyclic AMP, drives the pigment master-regulator MITF, and shifts production toward eumelanin.[2] When MC1R signalling is weak, the balance tips toward pheomelanin: the visible result is red or blond hair, fair skin that burns rather than tans, and freckling.[2]

The system also has a built-in brake. Agouti signalling protein antagonises MC1R, lowering its activity — the same mechanism that produces banded coat colour in other mammals.[1]

The melanocortin pigment switchα-MSH activates the MC1R receptor, switching melanocytes from pale UV-vulnerable pheomelanin to dark protective eumelanin — darkening a lizard and tanning human skin so eumelanin absorbs UV before it damages DNA.α-MSHMC1Rmelanocyteeumelaninthe protective pigmentThe demonstrationThe translationmelanophores disperse pigment — dark in minutesUVeumelanin absorbs UV — shields DNApheomelanin · fair, UV-vulnerableeumelanin · tanned, UV-protective
One molecule, one switch. α-MSH activates MC1R, flipping melanocytes from pale pheomelanin to dark eumelanin — the signal that darkens a lizard in minutes is the same one that tans human skin, where eumelanin then absorbs UV before it reaches DNA.

The "red hair" variants

MC1R is one of the most variable genes in the human genome. A handful of strongly penetrant loss-of-function alleles — classically R151C, R160W, and D294H — are associated with the red-hair, fair-skin phenotype. These variants largely fail because the mutant receptor is mis-trafficked and under-expressed at the cell surface, so less signal gets through even when α-MSH is present.[3]

Why it matters: skin cancer risk

Carrying red-hair-colour MC1R variants raises the risk of cutaneous melanoma and of non-melanoma skin cancers — and the effect persists even after accounting for fair skin and red hair, pointing to a contribution beyond visible pigmentation.[2] Part of the explanation is that pheomelanin amplifies UV-induced DNA damage, and may even contribute to melanoma formation through oxidative damage in the relative absence of UV.[2] Strong MC1R signalling, by contrast, supports not just eumelanin synthesis but also DNA repair and antioxidant defences in melanocytes.[2]

Beyond pigment: pain and anaesthesia

One of the strangest facts about MC1R is that a pigment gene reaches into the nervous system. Because the receptor is also active in neural tissue, red-hair variants track with measurable differences in how people experience pain and respond to anaesthesia. In a controlled study, red-haired women needed about 19% more of the anaesthetic desflurane than dark-haired women to block a response to a painful stimulus.[5] And people carrying two variant MC1R alleles show altered responses to certain opioid painkillers — an effect first mapped in mice, then confirmed in humans, and partly sex-specific.[6]The mechanisms are still being untangled, but the headline is clear: the "redhead" receptor is not only about colour.

Beyond pigment: immunity and therapy

MC1R is not confined to the skin. It is also expressed on immune cells, where melanocortin signalling is broadly anti-inflammatory — one reason the receptor is of interest well outside dermatology.[4] Therapeutically, the α-MSH analogue afamelanotide is an MC1R agonist used to raise protective eumelanin in erythropoietic protoporphyria; see the therapeutics section for that entry, and the overview pillar for how MC1R fits the wider system.

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Common questions

What does the MC1R gene do?

MC1R is the receptor on pigment cells that decides which type of melanin they make. Strong signalling produces brown-black eumelanin that absorbs UV and protects DNA; weak signalling — as with the red-hair variants — produces reddish pheomelanin, giving red or blond hair, fair skin that burns, and freckling.

Why do people have red hair?

Red hair comes from loss-of-function variants of MC1R, classically R151C, R160W and D294H. With MC1R signalling weakened, melanocytes default to reddish pheomelanin instead of protective eumelanin — the pigment behind red hair and fair, freckled skin.

Does MC1R affect skin-cancer risk?

Yes. Red-hair MC1R variants raise the risk of melanoma and other skin cancers, and the effect persists even after accounting for fair skin and red hair. Pheomelanin offers little UV protection and can add oxidative DNA damage, while strong MC1R signalling supports DNA repair and antioxidant defences in melanocytes.

Is it true that redheads need more anaesthetic?

There is real evidence for it. People with red-hair MC1R variants have been shown to require more general anaesthetic and to respond differently to some painkillers, because MC1R is also active in the nervous system. It is a striking example of a "pigment" gene reaching well beyond the skin.

References

  1. 1.Cone RD. Studies on the physiological functions of the melanocortin system. Endocr Rev. 27(7):736–49. 2006. link ↗
  2. 2.Nasti TH, Timares L. MC1R, eumelanin and pheomelanin: their role in determining the susceptibility to skin cancer. Photochem Photobiol. 91(1):188–200. 2015. link ↗
  3. 3.Beaumont KA, et al. Altered cell surface expression of human MC1R variant receptor alleles associated with red hair and skin cancer risk. Hum Mol Genet. 14(15):2145–54. 2005. link ↗
  4. 4.Ramachandrappa S, Gorrigan RJ, Clark AJL, Chan LF. The melanocortin receptors and their accessory proteins. Front Endocrinol (Lausanne). 4:9. 2013. link ↗
  5. 5.Liem EB, Lin CM, Suleman MI, et al. Anesthetic requirement is increased in redheads. Anesthesiology. 101(2):279–83. 2004. link ↗
  6. 6.Mogil JS, Wilson SG, Chesler EJ, et al. The melanocortin-1 receptor gene mediates female-specific mechanisms of analgesia in mice and humans. Proc Natl Acad Sci USA. 100(8):4867–72. 2003. link ↗