Picture courtesy Prof. James McInerney
With temperatures soaring this week, it’s definitely time to slap on the sunscreen, particularly for those with fairer skin and red hair. But where does red hair come from, what is its genetic basis and where is it most common?
Most people with red hair have two recessive alleles (alleles are different forms of the same genes inherited from your parents) for the gene coding for the MC1R protein. These ‘homozygous recessive’ individuals produce a higher level of the yellow-reddish phaeomelanin pigment to those with two dominant alleles (homozygous dominant) or one dominant and one recessive (heterozygous), where the brown-black eumelanin is more prominent.
Humans can vary more than 100-fold in their sensitivity to the harmful effects of sunshine, in the form of UV radiation, due primarily to skin pigmentation. Individuals with fairer skin are more sensitive to UV and more susceptible to most forms of skin cancer. On the other hand, they are less likely to be Vitamin D deficient and more likely to benefit from UV treatment for skin disorders such as psoriasis.
Recent research has also shown a link between red hair and sensitivity to pain, with the mutated MC1R protein the likely culprit. It seems that redheads feel pain differently to others, with one 2005 study revealing them as being more sensitive to thermal (heat) pain and another finding they require larger doses of anaesthetic, while a third study demonstrated an increased resistance to certain physical pain (e.g. pinpricks).
As you can see from the distribution map, large parts of Ireland, Scotland and Wales have a population with >10% red-headed individuals, with the frequency decreasing as you travel away from these islands. However, you may not have realised that red hair is common in parts of Russia, and even further afield in Turkey and the Middle East.
If you’re interested in finding out more, check out the original paper linking MC1R with red hair and fair skin and the more recent The Genetics of Sun Sensitivity in Humans.