(WYTV)- Take a deep breath.

You’re using both nostrils but when you breath normally, one nostril is working more than the other, and they trade off. German physician, Richard Kayser, first described this effect in 1895.

A head and neck doctor at the Cleveland Clinic, Dr. Michael Benninger, says that we breathe about 75% from one nostril and 25% from the other, and they switch off around every two hours.

Bring your nose near a mirror and breathe…you’ll see the difference when you exhale. Doctors call this the nasal cycle. We typically don’t notice this unless we’re stuffy. Why does this happen?

There’s a theory: the alternating airflow allows each nostril to stay moist so no one side gets too dried out. You may notice your nasal cycle more when you sleep, especially if you’re a side sleeper, in that case, gravity will cause the lower nostril to become less congested.

Things aren’t quite the same when you have a cold that stuffs up both nostrils. In that case, your nasal cycle will have little effect.