At any given moment, if you’re breathing through your nose, the lion’s share of the air is going in and out of one nostril, with a much smaller amount passing through the other. Every few hours, your autonomic nervous system — which takes care of your heart rate, digestion and other things you don’t consciously control — switches things up and your other nostril does all the heavy lifting for a while. No one is sure why the nasal cycle occurs, but the popular theory is that it has to do with allowing moisture to build up on one side so that it doesn’t get too dry. Most people aren’t even aware of the nasal cycle, though it could become more noticeable during sleep. If a person lies on their right side, for example, gravity will cause that lower nostril — the right one — to become more congested. If the cycle has designated the right nostril to be naturally more congested at the time, that’s no appreciable effect. However, if the nasal cycle has made the left nostril more congested and the right nostril is congested because of side sleeping, breathing may become difficult and cause the person to wake up. Although your nose may feel stuffy when you have a cold, that’s not due to the nasal cycle. In general, both nostrils are congested when you’re sick, so you’re going to have trouble breathing through your nose no matter where you are in the cycle. There are ways to decongest both nostrils at once, which can temporarily lead you to breathe more equally out of them until the nasal cycle resumes. Medications such as nasal decongestant sprays, as well as exercise, can have the same effect.
