When you go into the cold, changes in the water pressure of capillaries in your nose are triggered by the interaction between signalling chemicals and receptors that also involved in inflammation. These are the same signalling pathways that cause these symptoms in hayfever.

How cold weather triggers these pathways is not clear, but it involves the activation of so-called capsaicin receptors. The fact that this sounds like capsicum is no accident – these receptors are responsible both for the burning sensation in your nose when you suck in a noseful of cold air and for the dripping nose you get when you eat a hot curry.

Believe it or not, the formal diagnosis of rhino-rrhoea, literally translates from the ancient Greek into ... nose-runny.

As you'll notice as the weather gets cold, a runny nose can come about from walking from a warm environment out into the cold. Although it's a common phenomenon, there is no formal explanation.

The runny nose seems to occur in order to maintain a certain balance in the humidity and temperature of the mucous layer lining your nose. Mucus is important for trapping dust, pollen and bacteria that might otherwise end up in your lungs, but it only works if it's damp and sticky.

Damp mucous layers condition the air that enters your lungs to prevent those linings drying out.

Scientists have probed the proboscis of willing subjects, and found surprisingly that the relative humidity of the nasal cavity remains consistently at around 100 per cent, regardless of the temperature of the air inhaled.

This humidity is maintained because of water vaporisation by the nasal mucosa, which channels through a dense network of capillaries. Temperature is important, because cold air has a much lower absolute humidity than warm air.

Inhaling cold air causes a sudden drop in the water capacity of the nasal cavity. Since nasal mucosa are not so quick to adapt, it pumps water to the surface that cannot be absorbed by the air.

Water drops bead from these capillaries by osmosis (where molecules pass through a membrane). That water is your runny nose.

Response by: Dr Michele Cavazzini, postdoctoral medical researcher

Brought to you by the Fuzzy Logic science show, 11am Sundays on 2XX 98.3FM. Send your questions to askfuzzy@zoho.com