Why Your Nose Runs in Cold Weather

Step outside on a January morning and your nose starts leaking within minutes. The physiology behind it has two parts, and neither one is a cold.

The first is simple condensation. You exhale air at roughly 37°C and close to 100 percent humidity. That air hits the inside of your nostrils, which are only a degree or two warmer than the outside, and the water vapor drops out onto the mucous membrane like steam on a cold window. Some of it pools and runs.

The second is an active response called cold-induced rhinorrhea. Cold, dry air irritates the nasal lining. Receptors fire, blood flow to the nasal turbinates increases, and the mucosa releases a thin, watery fluid to humidify the incoming air before it reaches your lungs. The nose is, structurally, an air conditioner: a long turbulent passage designed to warm and wet whatever you breathe. When the task is hardest — cold, dry winter air — production ramps up.

Outdoor winter air in most of the northern hemisphere has a lower absolute humidity than the Sahara. Your nose is compensating in real time. The system is efficient enough that air arriving at the trachea is within a few percent of body temperature and fully saturated, regardless of how dry it was outside.

The condition has a formal name — cold-induced rhinitis, or 'skier's nose' — and it affects most people. Antihistamines don't help; the trigger isn't allergic. A small body of trials finds modest relief from ipratropium nasal spray, which blocks the nerve signal that opens the secretory tap.