Nearly naked and immersed in ice cubes up to the neck, two Chinese men recently duked it out in a cold-endurance contest for two hours. My low-temperature-loving grandfather, a member of the polar bear club, used to plunge regularly into freezing Finnish waters as a form of leisure. No matter the weather, my son, too, seems happy to storm the playground, sweating under his Siberian hat, while my own toes have been frozen for months. Why are some people so much heartier in the cold?
The Web variant on this is, of course, "Why are women always cold?," a perennially popular Google search. Men gripe about their female colleagues who want the office toasty. There are even dual-control heated blankets that allow couples to dial up two different temperatures for the night. Yet the data on men and women are full of curlicues, as the New York Times noted in 2009, even when it comes to simple body temperature. Some studies suggest that women have slightly higher core temperatures than men but also slightly colder hands. These papers don't deal with how men and women react to freezing cold, though. Other research immerses intrepid subjects in chilly baths, and one small example suggests that gender isn't the key to how people respond. Instead, body fat and the body's surface-area-to-volume ratio are. Still, none of this speaks to perception, which is a big part of heartiness. How cold you feel, and whether it bothers you, researchers say, also depends on factors like how tired you are, whether you're hungry, or whether you've come from a cold place—making it idiosyncratic and variable, even in a single day. Then again, according to some of the same researchers, both men and women may increase their endurance by taking cold showers or running around half-naked in the snow, in case that sounds appealing.
Normal body temperature was defined in the 19th century, when German physician Carl Reinhold August Wunderlich compiled roughly a million armpit temperature readings from 25,000 patients. He reported an average measure of 98.6 degrees Fahrenheit for healthy adults. Wunderlich also noted that women tended to have slightly higher body temperatures than men. In the early 1990s, researchers in Maryland took the oral temperatures of 148 patients and in the Journal of the American Medical Association agreed with Wunderlich's gender difference, finding that women's body temperature was, on average, 0.3 degrees higher than men's (98.4 degrees for women versus 98.1 degrees for men).
Then came a twist: A few years later, researchers in Utah argued that women have warmer hearts but colder hands. In work published in the Lancet, physician Han Kim and his colleagues surveyed 219 men and women, from babies to octogenarians, and measured the temperatures in their ears and on their fingernails, which they took to be measures of core and hand temperature, respectively. They reported that for women, core temperature was on average 0.4 degrees higher than for men (97.8 degrees instead of 97.4 degrees). But hand temperature was 2.8 degrees lower (87.2 degrees instead of 90.0 degrees). These findings come with caveats: Core temperature also varies with age, levels of fitness, and, for women, menstrual status, which could have influenced the authors' averages. Still, their findings make some physiological sense. Women do tend to have more body fat, which holds in heat and yet, counter-intuitively, may make the extremities colder, says Mike Tipton, a physiology professor at the University of Portsmouth. (He says that fatter people also tend to have colder hands.)
But what about how people react when exposed to a drop in temperature? For the purposes of search and rescue, Canadian researcher Peter Tikuisis and his colleagues wanted to model how people would fare when trapped under an avalanche or in a freezing stream. So they immersed 11 women up to their necks in chilly water, monitored their rectal temperatures, and compared the results to previous work with 14 men. They found that the rate at which rectal temperature dropped was related to peoples' body fat as well as their surface-area-to-volume ratio. People who are smaller, as women on average are, tend to have higher surface-area-to-volume ratios, which means they're likely to lose heat and to experience drops in core temperature more quickly. Still,if a man and woman were matched for both measures, they should have the same response to cold, says Tikuisis. Of course, his study was small, as others of its kind have been. (Are you lining up to volunteer?)
So what does this mean for how cold we feel or how merrily we go forth on a freezing January day? Our perception of cold may depend mostly on changes in skin temperature, which starts dropping first when we step outside. People feel cold well before their core temperatures dip, says Tikuisis. So if women tend to start with colder hands, as the Lancet paper suggests—or if they shunt blood more readily from the extremities to the core, as some researchers believe—they might feel uncomfortable faster.
At the same time, feelings of cold and howls of protest probably also depend on all those other variables related to hunger and tiredness. In other words, even if gender is somewhere in the mix, so are lots of other particulars. What explains, say, the swimming phenom Lynne Cox, who covered more than a mile in Antarctic waters wearing only a bathing suit? Some of us relish the feel of snow on naked skin, or at least condition ourselves to be utterly stoic. Others of us, male and female, will hug a space heater and count the days till spring.