Scientists Finally Prove Why Cold Weather Makes You Sick

Scientists may finally be able to confirm the widely-held suspicion that bad weather can make you sick.

While the common cold’s name seems to imply that cold weather is responsible for the nose-running, throat-burning misery, the scientific community has been unable to establish exactly how a chill in the air might lead to the sniffles—until now. Just last week, a team of scientists from Yale University announced their discovery that lower temperatures weaken the nose’s first line of immune defenses.

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New research reveals that cold weather makes it harder to fight off a cold infection.

The researchers started out by modifying a strain of rhinovirus—the kind of virus that causes most colds—to infect mice. (The modification was necessary because most cold viruses that infect humans don’t seem to infect rodents). They then tested how well the cells that line mouse airways fought off the virus at different temperatures, finding that cooler temperatures meant a more sluggish immune response and a greater susceptibility to infection.

Here’s Carl Zimmer, reporting for the New York Times on Thursday:

At body temperature, the cells responded with a sophisticated defense, sending out warning signals to uninfected cells around them. Those cells prepared an arsenal of antiviral proteins, which they used to destroy the rhinoviruses.

But at a relatively cool 91.4 degrees Fahrenheit, Dr. Iwasaki and her colleagues found, things changed.

The neighboring cells only managed a weak defense, allowing the rhinoviruses to invade them and multiply. This result pointed to an explanation for why rhinoviruses plague humans at low temperatures: In cool conditions, the immune system somehow falters.

Previously, scientists thought the association between winter and colds might be more behavioral than biological: an increased number of people sharing air inside warm spaces could lead to more transmission of the virus. This study adds biological evidence to mix, revealing that cold weather actually hampers our defenses against rhinovirus infection.

More work will need to be done to demonstrate that this phenomenon is true for living animals as well as for cells in a dish—and then to demonstrate it in humans—but this study nevertheless provides an interesting clue to the mysterious connection between cold, and colds.