It’s the season for fuzzy sweaters and heavy coats, as well as colds and flu. But what does cold weather have to do with catching a cold?

“Cold weather is just the straw that breaks the camel’s back in terms of having more stress and decreasing your immunity,” she said.

The dispute about whether cold causes colds stems from scientific debates in 19th-century France, LaGreca notes. For Louis Pasteur, who promoted the idea of germ theory in modern medicine, the virus was primary. However, Pasteur’s contemporary, Claude Bernard, argued that infections hinge not on microbes, but on environmental conditions that allow microbial invaders to flourish.

In the 20th century, scientists overwhelmingly supported Pasteur’s position. They focused on the pathogen as the root of illness and relied exclusively on microbe-destroying medicines—like antibiotics—for treatment.

However, emerging research on the microbiome and our evolving understanding of how the immune system works gives increasingly more credit to Bernard’s view that environmental conditions profoundly impact illness. It’s the same view that ancient Chinese medicine has held for centuries.

“The terrain is tremendously important, and that’s exactly how the Chinese thought about it,” LaGreca said.

To deal with the added stress of winter, ancient Chinese texts give lifestyle instructions about how to live healthfully during the season. When nature is cold, dark, and still, we are also encouraged to become more aligned with this yin energy. That means getting more rest and cultivating a gentler, more contemplative spirit.

However, such stress-minimizing advice can be hard to follow in our yang-dominant modern society, which demands we keep a fast pace all year long.

“We shouldn’t be keeping the same schedule, but that’s the world we live in,” LaGreca said.

These winter lifestyle recommendations are intended to preserve and strengthen something Chinese medicine calls wei qi, or defensive energy. Think of wei qi as a protective layer of energy that covers your entire body. It is often compared with the modern notion of the immune system.

Strong wei qi prevents the damaging effects of cold from invading the body, while weak wei qi leaves us susceptible to illness.

“It makes sense that there’s cross-talk between our immune system and emotions in ways that will protect us,” Miles said. “If your wei qi is deficient, you feel like you want to curl up, stay at home, and not be around people. But if you wei qi is prolific, you want to have a party and invite people over.”

One way to support wei qi function is by wearing warm clothes. Consider wei qi to be your base layer, while your sweater, scarf, and anything else you pile on help provide added insulation. The Chinese believe it’s especially important to keep the neck and abdomen covered because these areas are particularly vulnerable to the cold.

However, even the best coat can’t replace good wei qi. You can replenish your wei qi with rest and hot, nourishing meals. Miles recommends pungent and bitter foods (like garlic and shiitake mushrooms) to help strengthen wei qi.

Think about how a 50-degree-Fahrenheit day is considered balmy in Alaska, but unbearable in New Orleans. The reason is hormesis, a biological principle in which body function improves with small doses of something that would otherwise harm it. For example, too much weight can injure a muscle, but repeatedly subjecting that muscle to a little resistance can make it stronger. The same holds true with cold.

“We say that cold invigorates the yang, which means it calls it to the surface,” said LaGreca. “If you stay in the shower with cold water beating on you, at some point you’re going to feel some warmth come to the area as your body compensates for that cold.”

Using the hormetic principle to your advantage requires having a feel for how much cold you can stand. Taking on more stress when you’re already run down is foolish. But if your wei qi feels robust, spend some time outside.

This same sense of balance applies to physical activity. While winter is a time for rest, we can’t go totally lax. Miranda advises her patients to maintain a sustainable exercise routine.

“Even if it’s just walking for 10 minutes, that’s going to get the circulation going, but it’s also for stress relief,“ she said. ”When people are stressed, their immune system declines.”

Another wintertime habit to stay diligent about is washing your hands. This doesn’t boost your immune system, but it will minimize your exposure to the viruses and bacteria that can cause illness.

However, there’s no need to micromanage when it comes to protecting yourself. In Chinese medicine, paying attention to balance in all areas of life is the ultimate goal, and the main protector against illness.

“Just be mindful of things,” Miranda said.