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La Republicca May 30, 2026 | Heat and the Red-Hair Gene

February 6, 2026

“Those Who Have It Feel Temperature More”

By Elena Dusi, Rome

What if Sinner’s Achilles heel were actually his red curls?

To explain his sudden loss of energy, attention has turned to a study linking the MC1R gene—the gene associated with fair skin, freckles, and red hair—to the ability to tolerate heat.

Watching Sinner struggle under the sun at Roland Garros, both Boris Becker and Jim Courier recalled how much they themselves suffered during extremely hot matches.

The study on MC1R dates back to 2005 and arose from observations made by several anesthesiologists. They noticed that patients with red hair required more anesthetic to become unconscious.

Researchers at the University of Louisville recruited 30 red-haired volunteers and 30 dark-haired volunteers. They exposed the participants’ fingers to painful hot and cold stimuli and found that those with dark hair had greater tolerance.

“This does not demonstrate that people with red hair are less resistant to heat during sports, nor that they are more susceptible to heat stroke,” explains Daniel Sessler, who led the study and is now Professor of Anesthesiology at the University of Texas in Houston.

What does it demonstrate, then?

“People with red hair are more sensitive to painful stimuli caused by heat or cold and are generally more resistant to anesthetics and sedatives. There is no evidence that heat during physical exercise causes them to fatigue more quickly. However, that possibility cannot be ruled out either.”

So do they suffer more from heat during sports or not?

“We do not know. We only observed effects on the skin. At the cutaneous level there is indeed greater sensitivity to temperature and pain. But no one has ever conducted an experiment to determine whether the effects of the MC1R gene also influence the body’s ability to regulate temperature during intense physical exertion.”