Did you know your nose has a “cycle” in which your breathing alternates between nostrils? Your brain signals one side of the nose to become congested for a while, slowing down the flow of air on that side, then it clears, and the other side does the same. Most of us are completely unaware of this phenomenon, but it happens in up to 80% of adults.
The nasal cycle is controlled by the autonomic nervous system (ANS), the unconscious controlling system of the brain. And here’s the really fascinating part – it accomplishes this feat by dilating or constricting blood flow to structures inside the nose similar to the tissues found in the penis and clitoris (called venous cavernous tissue)! This is the tissue that swells during sexual arousal without us thinking about it.
The length of the nasal cycle, on average, is 2 ½ hours on each side but can be anywhere from 30 minutes to 6 hours. While most people have a nasal cycle, about 20% do not and they breathe through both sides equally all the time. The length of the cycle varies in different people and in the same person over time, and the length of the cycle changes over our lifetime, too. Most newborns have no nasal cycles at all, they increase with age until adulthood, then decrease again in the elderly.
The nasal cycle has several benefits:
It helps keep the nose moist. When one side becomes somewhat congested, the flow of air through that side slows down, reducing the drying action of the air passing through and allowing it to rehydrate. Essentially, this gives that side of the nose a rest while the other side takes over for a while.
The nasal cycle tends to be longer at night, lining up with our REM (dream sleep) cycle and with sleeping position. Some researchers have suggested this may be a mechanism to encourage us to turn over in our sleep to prevent bed sores.
The nasal cycle also helps our sense of smell. To experience a scent, tiny molecules need to connect with the olfactory organ in the nose. Some molecules attach easily and benefit from faster moving air to reach the organ of smell before sticking elsewhere in the nose. Others are less sticky and benefit from slower air movement that allows them time to attach to the olfactory organ as they pass it. So, having a fast and a slow side to your nose allows more scent molecules to reach and attach to the smell mechanism in the nose, improving your sense of smell. As I learned this, I couldn’t help thinking that smelling something awful means tiny molecules of the substance must have entered the nose in order to detect the smell… but ignore that thought and let’s move on!
The rate of mucous clearance is also affected by the nasal cycle, although it’s debated which part of the cycle helps more. Drainage of mucous is thought to help sweep out particles and bacteria that our noses filter from the air we breathe so they don’t accumulate, causing problems in the nose.
Of course, the nasal cycle has nothing to do with infection or nasal disease. It’s a normal function of the body that operates without our knowledge or awareness. However, it is noticed more often in people with underlying conditions such as a deviated septum, where the internal dividing structure of the nose is off-center. It’s important to be aware of the nasal cycle, however, when diagnosing a potential problem in the nose.
Why does your nose run when you’re outside in cold weather?
“Cold-induced rhinitis” or “skier nose” is probably caused by a combination of factors:
Cold air irritates and dries the nasal membranes. In response, the mucosal lining of the nose produces more mucous to protect the lining and keep it moist. Cold air also needs to be warmed to protect the lungs from damage and the nose itself needs to be protected too. So, your brain increases blood flow to the nose and dilates the blood vessels there to maintain the warmth and warming action of the nose as the cold air passes through. This blood vessel dilation causes loss of fluid into the nose – up to 300-400 ml daily!
Condensation is also thought to be a factor, although likely minor in comparison. Cold air holds less moisture than warm so, when the warm air you exhale contacts the cold air outside, small droplets of condensation can form when the warm air from your lungs meets the cold air outside, mixing with the mucous from your nose. You sometimes see this as frost on moustaches and scarves in chilly weather.
Pre-warming the air that reaches the nose can help prevent cold-induced rhinitis. This can be done by wearing a scarf over the nose and mouth when you go outside in winter and breathing through the scarf. It keeps the end of your nose warm too! Of course, if you wear glasses, this could create problems with fogging. Taking a tip from COVID mask suggestions, however, you could try placing a folded tissue under the top edge of the scarf to block your breath from escaping upward toward your glasses. Another idea would be to fold the scarf over 2 or 3 twist ties that can then be bent to help seal the upper edge. And, of course, you could try wearing your COVID mask as a face/breath warmer, perhaps with an extra scarf over top to increase the insulation. I’ve noticed that a mask alone worn outside in cold weather quickly results in the mask becoming damp because of condensation. I’ll experiment this afternoon when I take my daily walk to the mailbox…
Meanwhile, my hubby jokes, “Up your nose with a rubber hose might be an alternative!”
References:
The nasal cycle: a comprehensive review – Rhinology Online
Why does your nose run when it’s cold? – The University of Queensland, Australia, Faculty of Medicine
Cold Weather and Runny Noses – Verywell Health
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