Why does my nose run in cold weather?
• This is caused by condensation and evaporation. In cold air there is not much water vapour but warm exhaled air is almost completely saturated with water vapour from its passage over the warm surfaces of the lungs and airways.
When the exhaled warm and moisturised air passes over the surface of the nasal mucosa that has been cooled by the cold air on its way into the lungs, it condenses, just as it does if you blow exhaled air towards the colder surface of a window pane or a mirror. As the nasal mucosa cannot take up all the moisture that condenses on it, the nose runs to get rid of the excess. The water running out of the nose is clear and clean condensed water, and is not a sign of an infection.
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In the Arctic this constant running nose is a nuisance until you learn either to avoid breathing through the nose or to breathe in through the nose and out through the mouth. In fact, the original Arctic mitten has a piece of soft fur on the back to wipe up the surplus water running out of the nose. After the water has frozen, the ice crystals can easily be shaken off.
“In the Arctic a constant runny nose is a nuisance, so you learn to avoid breathing through it”
The same condensation/evaporation problems arise when you are eating warm soup. Here the moist and warm air from the ingested soup will tend to condense on the nose mucosa and create the same condition. By carefully adjusting your breathing you may overcome the problem by regulating the direction of the airflow over the mucosa of the nose, or by simply only breathing through the mouth.
Leif Vanggaard, Hellerup, Denmark
• Apart from being the sense organ involved in smell, the nose is the main route by which air enters and leaves the respiratory pathway. Before it reaches the lungs it needs to be warmed, moistened and cleaned and all these conditioning processes begin in the nose.
As those of us who suffer from frequent nosebleeds are only too aware, superficial blood vessels in the nose serve to warm the air. If you peer up someone’s nose (perhaps do this when no one else is looking) you will see a number of large black hairs, which serve to filter out larger particles of dirt. Mucous secreted by glands lining the nose, aside from moistening the air, also trap smaller particles. The epithelial cells lining the nose have small hair-like structures called cilia on their surface, which beat to move the resulting mess towards the back of the throat where we swallow it, although the uncouth may choose to spit it out.
In cold weather the cilia on the epithelial cells beat less efficiently and the mucous dribbles out of the front of the nose rather than being shepherded backwards.
Similar ciliated cells line the windpipe, or trachea, where, along with mucous secreted by goblet cells, they trap dirt that has got through the nose and mouth. These cilia beat to move the material up towards the throat.
One of the reasons not to smoke is that it destroys these cilia, resulting in smokers developing a characteristic cough needed to move the impurities away from the lungs’ respiratory surfaces.
Ron Douglas, Saffron Walden, Essex, UK