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 cold in, say, autumn, compared to the spring.