Home heating and humidity may also play a role in winter health, Dr. Spinner said. Running the heat to keep the house warm also dries it out — and can dry out our sinuses, too. “When you don’t have good nasal mucus flow, it’s harder for the immune system to work against the virus,” he said.
Research also suggests that low indoor humidity may promote the transmission of flu. With high humidity, flu viruses expelled in a sneeze, for example, tend to attach to water molecules and may drop out of the air before they can trigger a new infection. In a dry room, those flu viruses often continue to float around until they reach their next victim.
There are also some scattered laboratory studies that suggest being cold might weaken the immune system, making us more vulnerable to those viruses. A 2017 study found that immune cells that are chilled are less effective at fighting off viruses, at least in a lab dish, making it “easier for the virus to infect,” said Dr. Prasert Auewarakul, a co-author and professor of virology at the Faculty of Medicine Siriraj Hospital, Mahidol University in Thailand.
In a 2005 study by other researchers, college students whose feet were soaked in cold water for 20 minutes a day were more likely to get sick than those not exposed to the cold. And research in mouse cells suggests that rhinovirus, the common cold virus, replicates faster at cold temperatures, Dr. Auewarakul added.
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