That first cold spell of the season always feels especially harsh.
If you’ve ever wondered, from beneath several layers of clothing, whether you were overreacting to those frigid early fall days, take solace. It may not just be in your head: The human body takes time to acclimate to the cold.
“We kind of get a global response over time over the winter so that a 50-degree day in, say, February, feels glorious, whereas at this time of year it feels chilly,” said John Castellani, a physiologist who specializes in cold weather research at the United States Army Research Institute of Environmental Medicine in Massachusetts.
Some experts argue that the shift in perception is mostly psychological, but others, including Dr. Castellani, say there’s more to it: The evidence suggests that the body grows to tolerate the cold over time.
Here’s a brief look at what we do and don’t know about how the body responds to the lower temperatures of autumn.
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We’re all snowflakes
As anyone who has fought over the thermostat knows, people experience temperature differently, sometimes dramatically so.
A variety of factors explain why. Studies have found, for example, that larger people shed more body heat in the cold than smaller ones because they have a greater surface area over which to lose it. People with more fat beneath their skin lose less heat because it serves as insulation. And older people can have more difficulty with frigidity than the young.
Psychology can play a substantial role, too. As can behavior: Humans excel at limiting their exposure to wintry conditions, which can dull the effects of the cold.
“There’s a classic saying that ‘man in the cold is not necessarily a cold man,’” said Mike Tipton, a professor of physiology at the University of Portsmouth in Britain who studies temperature regulation in the body. “We wrap up, we heat our houses, we wear clothes and we recreate our tropical origins next to the skin.”
How the body responds
When the temperature drops, sensors in the skin known as thermoreceptors detect that change and send signals to the hypothalamus, a small, versatile region of the brain sometimes referred to as the body’s thermostat.
To maintain a safe core body temperature, the hypothalamus may then direct the body to do one of two things. The main response is a process known as vasoconstriction: the tightening of blood vessels on the body’s periphery to shunt warm blood away from the extremities and skin and back toward the core. The body may also shiver to generate heat.
“When the skin senses cold temperatures, its first response really is to protect the inside,” Dr. Castellani said.
How the body adjusts
Over time, though, those responses can change.
Studies of people throughout the world have found that those frequently exposed to the cold simply begin to tolerate it more by shivering or constricting blood vessels less.
Indigenous populations in the Australian and African deserts and the Arctic, for example, have been found to have a less pronounced response to the cold than those not subjected to the same frigid conditions. (Temperatures in the deserts often plummet at night.)
The same has been found even among people subjected to the cold in more limited ways. For example, fishermen and fish filleters who work long hours with their hands in cold water have been found to have higher hand temperatures when their hands are placed in frigid water compared with control subjects. Similar effects have been found among slaughterhouse workers who routinely handle slabs of cold meat.
That, Dr. Castellani said, explains how a person in a cool climate might adapt to winter over time.
“We experience that cold air on our cheek all winter long, and basically that skin doesn’t constrict as much,” he said. “We’ve habituated in that area, and because the skin’s a little warmer that’s why it feels warmer. That’s why the cold October day feels much colder than that same day in February.”
