What Is the Normal Nasal Cycle and What Does It Do at Night?

What is the nasal cycle?

The inside of each nostril is lined with tissue that can swell or shrink as blood flow changes. Over a period of several hours, the lining on one side becomes a little more swollen while the opposite side shrinks. Then they swap. This automatic rhythm is called the nasal cycle.

Medical reviews describe the nasal cycle as a normal, alternating change in resistance between the two nasal passages that helps the nose warm, humidify and filter air more efficiently.

In most healthy people, the cycle:

• Takes about 2–6 hours per side
• Continues all day and all night
• Is so subtle that you don’t notice it when you’re upright and active

Why do you feel the nasal cycle more when you lie down?

When you lie flat, especially on one side:

• Blood flow shifts toward the lower side of the body and head.
• Veins in the lower nasal passage can swell more easily.
• The side you are lying on becomes naturally more congested, while the upper side opens.

This is why “one nostril blocked when sleeping on side and why it often switches sides when you roll over.

Sleep-medicine resources point out that lying down often makes congestion worse because of changes in blood flow to the nose and sinuses.

For most people, this is uncomfortable but completely normal.

Why Does Only One Nostril Feel Blocked—And Is That Normal?

Why one nostril gets blocked when sleeping on one side

When you sleep on your right side, for example:

• Blood pools more on the right side of your nasal lining.
• The right inferior turbinate (a bony structure covered in tissue) swells slightly.
• Airflow decreases on the right, and you mainly breathe through the left nostril.

If you flip to your left, the process reverses. This is why people often ask me “why does my nose switch sides when congested at night?”

It’s common for one side of the nose to feel more blocked than the other at any given time, and that side-sleeping can make this more noticeable by causing mucus to pool on the lower side.

When is one-sided congestion considered normal?

It’s usually normal if:

• It changes sides depending on posture.
• It improves when you sit or stand up.
• You don’t have constant blockage on the same side during the day.
• You have no alarming symptoms like severe facial pain, repeated nosebleeds, or loss of smell.

In that setting, the one-nostril issue at night is most likely nasal cycle and gravity, not a major disease.

How Do Allergies, Colds and Sinusitis Make Nighttime Blockage Worse?

The story changes when you add inflammation.

How common are nasal congestion and sinus issues in the US?

Nasal congestion and sinusitis are extremely common in American adults:

• A CDC analysis reports 28.9 million U.S. adults—about 11.6%—have diagnosed sinusitis.
• Large surveys suggest roughly 14% of U.S. adults have been diagnosed with chronic or recurrent nasal congestion or rhinosinusitis (PMC).
• Allergic rhinitis (hay fever) affects about 7.7% of U.S. adults each year, or around 19 million people,

So if your nose feels stuffy most nights, you’re not alone.

Why do allergies and colds matter more when you lie down?

Nasal congestion occurs when the tissues and blood vessels in the nose swell due to infections (like colds, flu or sinusitis), allergies or irritants such as smoke and pollution.

When those tissues are already swollen from:

• Seasonal allergies,
• Indoor allergens like dust mites or pet dander, or
• a viral cold or sinus infection,

Then lying on your side adds another layer of swelling. The result:

• One nostril may become completely blocked, not just mildly restricted.
• You may notice postnasal drip and cough when mucus drains backwards.
• If you already have chronic sinusitis, pressure and pain can increase.

The CDC notes that sinus infections often involve inflammation and fluid buildup in the sinus cavities, causing congestion and runny nose—symptoms that typically feel worse when lying down.