Women often get cold more easily than men — a mouse study offers hints why

It's a common observation that women often prefer warmer temperatures and feel cold more easily than men do, and the same trend appears among females of other species. Now, a study offers new clues as to what drives this preference — and testosterone may play a part.

Skin carries sensors to detect heat and cold that influence each organism's decision to stay in or move out of an environment. The new study, published Oct. 28 in the Journal of Physiology, found that these sensors activate at higher temperatures in female mice, which appears to shift their preferred temperature roughly 7 degrees Fahrenheit (4 degrees Celsius) higher than that of male mice. Testosterone seems to influence this difference in activation.

"You could say it's just a cute observation of no particular importance," said study co-author Peter McNaughton, a pharmacologist at King's College London who studies pain, thermal sensation and thermoregulation. "[But] it's got practical ramifications," in that it might be important in designing buildings and spaces that accommodate people, he told Live Science.

A distinct temperature preference

Proteins in the skin's nerve endings activate in response to warmth or cold. "You can look at them like little electrical generators in the nerve endings," said Dr. Michael Caterina, a neuroscientist at Johns Hopkins University who was not involved in the research.

When activated, these proteins allow charged ions to enter sensory nerve cells, which, in turn, transmit electrical signals to the brain. The circuits a given nerve cell connects to determines our perception of heat or cold, Caterina told Live Science.

Beyond humans, it is known that many female animals, including mice and birds, prefer slightly warmer temperatures than their male counterparts do. So the researchers set up an experiment to investigate these differences.

They put 30 male and 27 female mice on two adjacent plates of different temperatures — one at 91.4 degrees Fahrenheit (33 degrees Celsius) and another that varied between lower and higher temperatures. A camera tracked the mice's movements and calculated how much time they spent on each plate.

Both male and female mice spent more time at the 91.4 F plate when the second plate was cooler. However, when put next to a plate measuring 100.4 F (38 C), female mice spent significantly more time on the warmer plate than male mice did. The average preferred surface temperature was approximately 89.6 F (32 C) for male mice and 96.8 F (36 C) for female mice.

"Since the top of the cage was completely open, there was no question of the air temperature affecting the mice," McNaughton said, so the preference was driven solely by the sensors in their skin. The researchers also measured the internal and skin temperatures of the mice and confirmed that there were no significant differences between the sexes on those fronts.

The role of testosterone

The scientists explored what would happen if they genetically deleted the warmth-detector protein. In male mice, this reduced their avoidance of the warmer plate, suggesting this protein normally sends a signal that discourages them from staying on warmer surfaces. The mice's preferred temperature also rose to about 95 F (35 C), closer to that of females.

In female mice, deleting or blocking the protein did not have any significant effect.

The team then tried eliminating or blocking the coolness-detecting protein, finding that males and females didn't avoid the cool plates as strongly as they did before. Female mice also spent less time on the warmer plates, but males' preference for the warmer plates didn't change.

"Females are a little bit more responsive to activation of the cold receptor," Caterina said, "and a little bit less responsive to activation of the warmer receptor." That's despite the temperature-sensing neurons in both sets of mice working identically, the team found.

The researchers suspected that sex hormones might help to explain this difference.

They gave a group of male mice a drug that blocks the production of testosterone. Weeks after the treatment, these mice spent more time on the 38 C plate than males with normal testosterone. Meanwhile, female mice given testosterone lost their preference for warmer temperatures.

Interestingly, giving male mice female hormones, including forms of estrogen and progesterone, did not affect their temperature preferences. And blocking the hormones in female mice also had no effect. These hormones are known to influence other aspects of temperature regulation in the body, though, such as heat dissipation through the skin; but in this case, they didn't seem to affect animals' perception of temperature.

"So it really seems as though testosterone is the most important determinant," McNaughton said. But these changes were only partial; testosterone did not completely reverse the differences between the sexes. "So there is something else going on that we weren't able to identify," he added.

The exact mechanism for how testosterone impacts the sensor proteins is not clear. Because the effect happened over weeks, researchers suggested that it did not directly affect the temperature-sensing proteins. It might instead act indirectly by influencing the activity of genes, but further studies would be needed to confirm this idea.

Although the researchers did not conduct any tests in humans, McNaughton noted that the same sensor proteins are present in people and that studies with humans suggest that they behave in a similar way.

This research provides "valuable information" for understanding how the proteins responsible for sensing temperature work, Caterina said. Understanding these mechanisms could be useful for studying conditions like neuropathic pain, in which people's sensitivity to heat and cold is enhanced.

"What kinds of signals create our daily experiences around temperature is by itself very important," he told Live Science. "It's a big part of understanding ourselves as living beings."