The nasal cycle: why one nostril is often blocked

If one nostril feels more blocked than the other, that's usually the nasal cycle at work. Tissue inside your nose swells on one side and shrinks on the other, and the two sides switch back and forth over a few hours. It's normal, and most of the time you don't notice it.

What is the nasal cycle?

A 2016 study in PLOS One explains that airflow is greater in one nostril than the other because erectile tissue temporarily narrows one nasal passage more than the other. The side that's narrower alternates, and that pattern is called the nasal cycle.

Cleveland Clinic describes the same thing in terms of the turbinates, structures lined with blood vessels that help regulate airflow and filter particles. They swell and shrink in turn on each side. In the words of Cleveland Clinic's Dr. Michael Benninger, "every four to six hours, one side of the nose becomes more congested, and the other side decongests."

What makes one side swell?

One side of the nose swells because of uneven blood flow, which is how the 2016 PLOS One authors explain the physical mechanism. Erectile tissue at the front of the septum and on the lower turbinate fills with blood on one side more than the other, and that swollen tissue partly blocks the passage. The nervous system is involved, with blood vessels narrowing on one side while they widen on the other, though the authors note it may not be the only driver.

When the researchers sprayed a decongestant into one nostril of a volunteer, scans showed the tissue on that side shrinking and airflow rising as it did, which confirmed they were measuring the swelling itself. Decongestant sprays aren't a nightly tool, though. Decongestant spray rebound explains why.

How long does each phase last?

The 2016 study recorded airflow through each nostril separately for 24 hours in 33 healthy, right-handed adults. On average, the cycle was shorter while people were awake, at about 2 hours, than while they slept, at about 4.5 hours. People spent slightly longer with the left nostril dominant than the right.

The researchers also found that slower breathing was linked to a stronger cycle, meaning a bigger difference between the two sides.

The range between people was wide. Everyone in the study had a cycle, but the length of time one nostril stayed dominant ran from 15 minutes, the shortest the analysis could detect, to more than 10 hours. Earlier studies the authors reviewed put the switch anywhere from 25 minutes to 8 hours, with most falling between 1.5 and 4 hours while awake. So if your timing doesn't match the textbook, that's not a sign anything is wrong.

Over a whole day, the left and right sides came out roughly even on average, though some individuals leaned more to one side than the other.

Does the cycle change while you sleep?

Yes, the nasal cycle changes while you sleep. In the 2016 recordings, the nostrils switched less often during sleep, but the difference between the two sides was larger. In other words, sleep tends to bring longer, more lopsided phases, which may be part of why one blocked side can feel so obvious when you wake in the night.

Body position adds to it. The authors note earlier research showing that the longer you lie on one side, the stronger the effect becomes, and that it can flip the cycle so the upper nostril stays the open one. A practical upshot is that if the nostril on the pillow side is blocked, rolling onto your other side often lets it open up again over time.

What is the nasal cycle for?

Nobody is completely sure what the nasal cycle is for. The 2016 authors cite earlier work suggesting the alternation helps condition the air and clear out trapped particles and mucus. Other researchers have linked it to protection against infection. Their own theory is about smell. Because each nostril has a different airflow at any moment, each one is better at picking up different kinds of odors, which may widen the range of smells you can detect overall.

Why is my nose blocked at night while sleeping?

Your nose feels blocked at night because lying down narrows it a little, and the side you sleep on can make one nostril feel more blocked. Those two effects stack on top of the normal nasal cycle, which is why a blocked side is easier to notice in bed.

Lying down makes the whole nose a little narrower. A 2022 meta-analysis in The Laryngoscope, which pooled nine studies with 291 people, found that lying down increases nasal resistance and reduces nasal airflow. The effect was larger in people who snore or have sleep apnea than in healthy people, and the authors called this finding of utmost importance for those groups.

Which side you lie on matters as well. The 2016 study found that lying on one side was linked to greater airflow through the opposite nostril. Cleveland Clinic puts it in practical terms: it's common for the nostril facing down on the pillow to feel stuffy when you sleep on your side, and if that eases soon after you get up and move around, side sleeping is a likely cause.

Why is my nose stuffy at night? covers other common causes of night-time congestion.

Why does a cold make one side worse?

A 2021 review in Clinical Otolaryngology describes how infection with respiratory viruses increases the swings of the nasal cycle, which causes congestion and blockage on one side. The author points out that common respiratory viruses replicate well at the cooler temperature of the upper airways, around 32°C, but less well at body temperature, 37°C, and that congestion warms the lining of the nose. His conclusion is that congestion linked to the nasal cycle may act as a defence against respiratory viruses.

Cleveland Clinic makes a similar point from the patient's side: allergies, illnesses and colds can speed up congestion, so the normal cycle that usually goes unnoticed becomes obvious.

When is a blocked nostril not the nasal cycle?

A blocked nostril is probably not the nasal cycle if it stays on the same side. A blockage that comes and goes and switches sides fits the nasal cycle. One that stays on the same side and doesn't go away is different. Cleveland Clinic lists several other causes of one-sided blockage, including:

• A deviated septum, where the wall between your nostrils is off-center.
• Chronic inflammation and nasal polyps.
• Irritants such as smoke, strong odors, chemicals and dry indoor air.
• A foreign object in the nose, which is especially worth checking for in small children.

If one side is always blocked, see a doctor so they can look inside your nose and find the cause.

What can help when one side is blocked at night?

For general congestion from a cold or allergies, Cleveland Clinic suggests sleeping on your back with your head slightly raised rather than on your side. It also mentions humidifiers, hot showers, saline spray and neti pots as ways to ease congestion. Our guide on how to unblock your nose before bed goes through these in more detail.

Can you still use mouth tape and nasal strips?

Yes, most people can still use mouth tape and nasal strips with the nasal cycle. A partly congested nostril is a normal part of the cycle, and the other side is open at the same time. What matters is whether your nose as a whole lets you breathe comfortably with your mouth closed. The two-minute nose test is a quick way to check before bed.

If it does, mouth tape works as usual as a simple reminder to keep your lips together while you sleep. Our first-week guide shows how to start gently. If your nose feels tight overall at night, not just on one side, nasal strips are worth a look, and how nasal strips work explains what they do.

If you use mouth tape, skip it on nights when your nose feels blocked and wait until you can breathe comfortably through your nose again. That includes colds, when the cycle swings harder than usual. For more on this, see our nasal breathing articles.

If you want to try nasal strips, our pick is TitanAir Nasal Strips.

* This content is for informational and educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any disease or health condition. Talk to a qualified healthcare provider about your health.