I think he's asking about the common trap people seem to fall into where, trying to keep heat in, they shut down air changes too far. Human breath puts a surprising amount of moisture into the air, and cooking can too. If you let that build up and have a cold wall it can build up a film of damp very quickly and if it's left damp and cool it can encourage mould. That kind of bad air quality is far worse than a bit of a chill.