Scientists Solved the Mystery of Why Some People Shiver in the Cold While Others Wear Shorts

Shuffling outside in three layers and a parka to pick up mail or take out the trash on a winter afternoon, you notice your neighbor is running the same errand in a sweatshirt and shorts. Just the sight of this gives you the chills, as if you weren’t shivering already. Could there be some freakish biological reason that, unlike your neighbor, you can hardly even imagine yourself in something that isn’t heavyweight and lined with fleece when the sky is threatening snow?Like with plenty of other quirks of our daily lived experiences, the answer to that question is yes.Your tolerance of the heat or the cold may actually be determined at a molecular level. Researchers Peter McNaughton and Bruno Vilar of Wolfson Sensory, Pain and Regeneration Centre at King’s College London exposed mice to different temperatures and saw that female mice preferred higher temperatures than males. The mice were given a choice of two heated metal plates, and the females scurried to the warmer plate at 100.4°F (38°C) while males would crawl towards the cooler control plate kept at 91.4°F (33°C). It was only when the researchers began to alter certain genetic mechanisms that the mice changed their preferences.“Human females have a lower surface temperature and a higher central temperature than males and prefer a higher ambient temperature,” McNaughton and Vilar said in a study recently published in The Journal of Physiology. “Although the comfort temperature varies significantly among species, a sex difference in thermal preference is consistent in most bird species and in mammals such as mice.”The answer lies in ion channels, tiny pores in cell membranes that let electrically charged particles called ions flow in and out. Two of them, TRPM2 and TRPM8, work as temperature sensors. Among other functions, TRPM2 regulates adaptations related to heat, while TRPM8 is activated by cold. Mice were allowed to feel out the heated plates for half an hour and usually showed a final preference halfway through the time they were given. There was no significant difference between male and female mice when they had to choose between the control plate and one at a cooler temperature of either 82.4°F (28°C) or 73.4°F (23°C). Both the male and female mice preferred the control plate to anything cooler. But then things began to get heated.Distinct preferences began to appear when the mice had the opportunity to decide between the control plate and a warmer alternative. Most females began shifting over to the warm plate and spent more time there, while males, whose preferred ambient temperature is known to be about the same as that of the control plate, apparently found that more tolerable. Upping the temperature of one plate to 109.4°F (43°C) had the same effect. The biological females preferred an average temperature of 96.8°F (36°C) while males’ average preferred temp was 89.42°F (31.9°C). Core body temperature doesn’t explain the difference. Male and female mice have the same core temperature, but the females still went looking for more heat.Genetic experiments helped show what drives the difference. When researchers deleted TRPM2 in male mice, the males suddenly moved toward the warmer plate, just as the females did. Deleting TRPM2 in females barely changed anything. TRPM8 played a much more significant role. When it was blocked with an injection or deleted entirely, both female and male mice stopped avoiding the cold and readily moved onto the cooler plate. This shows that TRPM8 is essential for sensing cold. A third channel, TRPV1, turned out to matter only for detecting intense heat.Hormones explain part of the difference, and testosterone seems to be the main one. Lowering testosterone in male mice shifted them toward the females’ preference for warmth, and giving females extra testosterone made them more averse to heat. Estradiol and progesterone, the main female sex hormones, had no effect. Even so, testosterone didn’t account for the whole gap between the sexes.“The simplest explanation of these observations is that TRPM2 and TRPM8 are expressed in different peripheral thermally sensitive nerve terminals,” the researchers said, “where they drive the generation of action potentials that convey thermal sensation to the [central nervous system].”Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.