A runny nose often disappears during sleep, leading many to wonder why nasal passages quiet down during rest. This article explores the physiological reasons behind this change in nasal function.
What Causes a Runny Nose When Awake
The nasal passages are lined with specialized cells that constantly produce mucus. This mucus acts as a protective barrier, trapping inhaled particles such as dust, pollen, and microorganisms. When irritants or allergens enter the nose, the body’s immune response can trigger inflammation, leading to increased blood flow and heightened mucus production.
Tiny hair-like structures called cilia line the nasal passages, sweeping this mucus and trapped particles towards the back of the throat, where it is typically swallowed. When awake and upright, gravity assists this process, helping mucus drain downward and, when excessive, out of the nostrils. Exposure to cold air can also stimulate nerve endings, leading to increased blood flow and mucus secretion as the body attempts to warm and humidify the incoming air.
How Sleep Affects Nasal Function
One significant factor influencing nasal drainage during sleep is the change in body position. When lying down, the effect of gravity on mucus flow is altered; instead of draining out of the nostrils, mucus tends to accumulate and drain backward down the throat, a process known as post-nasal drip. This internal drainage means the mucus is still being produced and moved, but it is not visibly running from the nose.
The body’s autonomic nervous system also undergoes a shift during sleep, with the parasympathetic nervous system becoming more dominant. This system is responsible for “rest and digest” functions, which can lead to changes in blood vessel constriction and dilation within the nasal passages. Reduced sympathetic nervous system activity, which often triggers nasal congestion and a runny nose in response to irritants while awake, contributes to a less active nasal response during rest.
During sleep, exposure to environmental irritants and allergens is often minimized, especially if sleeping indoors. This reduction in triggers lessens the need for the nasal passages to produce excessive mucus. The body’s overall metabolism and circulation also slow down, potentially reducing inflammation and swelling in the nasal passages. Mucus consistency can also change slightly during sleep, sometimes becoming thicker due to less hydration, which may make it less prone to free flow from the nostrils.
When a Runny Nose Might Still Occur During Sleep
Despite the general tendency for nasal drainage to decrease during sleep, a runny nose can still occur. In cases of severe illness, such as a cold or flu, or intense allergic reactions, mucus production can be so excessive that it overwhelms the body’s ability to internally drain it. This can lead to visible nasal discharge even while lying down.
Mucus production continues, often resulting in post-nasal drip, which can cause throat irritation or coughing during the night. Conditions like sleep apnea or chronic snoring can also sometimes irritate nasal passages due to altered airflow dynamics, potentially leading to increased mucus production or congestion. Environmental factors, such as extremely dry or cold bedroom air, can also irritate the nasal lining, stimulating some mucus production during sleep.
Upon waking and returning to an upright position, gravity causes any accumulated mucus to drain more readily from the nostrils. This explains why a person might wake up with a feeling of congestion or experience a sudden onset of nasal discharge shortly after getting out of bed.