Any virus or bacteria usually enters the body through the nose. The tip of the nose then detects the germs quickly, long before they are detected by the nose itself – ie by the main part of our olfactory organ – according to one research result.

At this point, the immune cells that are permanently present in the nose begin to make billions of copies of themselves. These are called extracellular vesicles or EVs for short. ‘EVs may not divide like other cells, but they behave like little mini versions of cells specifically designed to kill viruses,’ Dr. says Benjamin Blair, director of the ENT department at the Massachusetts Eye and Ear Institute. “EVs act as decoys, so if you smell a virus, that virus sticks to those decoys instead of entering the body.”

When attacked, the nose ramps up EV production by about 160 percent, the study found, and is therefore — under average temperatures — well-armed for common viruses and bacteria. However, when the temperature drops to just above freezing point, things look different.

To simulate this, the research team exposed four study participants to a temperature of about four and a half degrees Celsius for 15 minutes and observed their nasal cavities. “We found that exposure to cold air can drop the temperature of the entire nose by up to five degrees Celsius.” This is enough to shut down the immune benefits of the tip of the nose, Blair explains. 42 percent of EVs got damaged in this cold.