On the one hand, our nose is a passageway for pleasant aromas and life-giving oxygen, and on the other – a constant source of snot. In the winter months we more often observe the not-so-pleasant function of the nose. If you have ever encountered mucus escaping from your nose at sub-zero temperatures, then you are familiar with rhinorrhea brought on by the cold. Rhinorrhea is the fancy medical term for a runny nose, which can be caused by several different factors. It could be a cold, an allergy and so on, but let us get back to the subject. Snot in cold weather can be explained by two natural sciences: biology and physics. On biology and snot. As far as the body is concerned, your nose works «overtime» when it is cold outside, to make sure that the air we breathe is suitable for the sensitive tissue of the lungs. Otherwise we would constantly suffer from pneumonia. Moreover, cold air tends to be very dry, so in order to humidify it the nose increases its production of fluid. This often leads to an excess of mucus, which often tries to escape out of the nose. On snot and physics. The second, related reason is explained by a branch of physics – thermodynamics. A small part of every exhalation is water vapour. This can be seen at cold temperatures: when warm air from our body is expelled into the cold, it condenses into a cloud of tiny droplets, allowing us to «see» our breath. This same principle is partly responsible for a runny nose in the cold. When the warm air inside the nostrils meets cold temperatures, the moisture collects together, forming large, heavy droplets that contribute to the formation of mucus. And what about athletes. People who exercise in the cold are especially prone to a runny nose caused by low temperatures. Constantly dripping snot is a real problem for athletes, since wiping it away while competing for first place is practically impossible. The condition even has a name – «skier's nose» (which, admittedly, sounds much cooler than «snotty face syndrome»).