Good Question: Why Does Your Nose Run When It's Cold?
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Audrey from Zimmerman asks: Why does your nose run when it's cold?
On a normal day, the human nose can produce about one liter of mucus. We don't know it, though, because most of it gets swallowed.
Our lungs don't like cold air because it's too much of a shock to the system. So, when we step outside into the cold, there's an increased blood flow to the nose. That causes extra mucous to form, which is used to warm up and humidify the air before it reaches the lungs.
Some of what people might consider as part of a runny nose is also water. The warm air a person breathes out condenses in the cold air, making little droplets of water.