Redheads have a genetic mutation which means their melanocytes have a faulty version of a key receptor and therefore cannot make dark pigment to get a tan. .

The end result is that gingers produce more opioid signals than people with other hair colours and complections and therefore have an elevated pain threshold. .

Redheads have a genetic mutation which means their melanocytes have a faulty version of a key receptor and therefore can not make dark pigment to get a tan.

Dr David Fischer led a previous study which found fiery-haired people cannot create dark pigment and tan as a result of a loss of functionality in melanocytes. 

Gingers, the rarest of human hair colours, like all people have a receptor on their melanocytes called melanocortin 1 which sticks out from the surface of the cell. 

Gingers, the rarest of human hair colours, like all people have a receptor on their melanocytes called melanocortin 1 which mediates production of dark skin pigment

This leads to a hormone level different to people of other complection and results in an elevated pain threshold (stock)

This therefore enhances the impact of  other hormones — not made by the skin pigment cells — which boost the effect of the pain-quashing opioid receptors.