Why Don't We Sneeze When We Sleep?

Sneeze is a reflex action of our body in response to a foreign matter or irritant in our nasal mucosa (the membrane which lines our nose). It is a sudden, involuntary ejection of air from our mouth and nose caused by an irritation in our nostrils. It expels air from the nose and mouth forcibly in a spasmodic, involuntary, explosive action mainly resulting from an irritation in the nasal mucus membrane. Note that sneezing is one of the most powerful reactions shown by the human body, as its spray can reach as far as 3 feet away from your nose.

When we sneeze, something probably tickles or irritates the inside of our nose. Sneeze, scientifically termed as sternutation, is the body’s natural way of eliminating this irritation from the nose. Here are the causes which can lead you to sneeze:

• Allergic rhinitis: Allergies are one of the most common causes of sneezing. You may be allergic to mold, dust, dander, pollen and hay fever. During this allergic reaction, histamines are released by the allergic cells in the nasal mucus membranes, leading to a sneeze. Rhinitis is when the mucous membranes enlarge due to this allergic reaction. Oral and nasal antihistamines can be effective in stopping sneezing caused by allergies.

• Infection: An infection in the respiratory tract, such as the common cold, can cause sneezing. A cold causes production of mucus, which ultimately stimulates the nerves in your nasal mucus membranes. If the cause of your sneeze is the cold, then antihistamines won’t be able to stop it. You would need help of certain medicines that can dry up your nasal secretions, but even these might not leave until the virus passes.

• Irritants: Pepper, perfumes, strong odors, tobacco smoke and other such chemical irritants can trigger sneezing. Bright light may also cause sneezing by creating a reflex connection between nose and eyes, stimulating nerves in the nasal mucus membranes.

The best remedy is to stay away from allergens and irritants which cause you to sneeze. Try to prevent infections by improving your immunity and staying away from people who are already infected.

Sneezes work by expelling mucus from your nose containing the irritants or foreign particles, cleansing your nasal cavities in the process. When we are awake, nerve cells inside the nose get stimulated due to allergens, particles and illness. This sends reflex signals to the brain to initiate a sneeze. We sneeze whenever an irritant stimulates certain parts of our nasal tissue. When the sinuses and areas inside the nasal cavity are stimulated, our brain receives a signal. It gets a message and sends signals to the central nervous system, causing our throat, chest and face muscles to sneeze.

When we sneeze, the palatine uvula and the soft palate depress, the back of our tongue elevates and it partially closes the oral passage. In doing so it gives way for the air to eject from the lungs and expel through the nose. Because the oral passage is partially closed, most of the air passes out through the mouth only. The extent and force of the air being expelled varies.

It is impossible to sneeze during sleep, likely due to something called REM atonia. It is a state of the body in which motor neurons remain static and the brain does not receive any reflex signals. It is our body’s natural system to keep us at rest. Even if your nasal passage is stimulated with some external factors, you will wake up from your sleep in order to sneeze. This means that when you sneeze, you are at least in a partially awake state.

In theory, we should actually sneeze more while we are asleep. This is because mucus membranes tend to swell while we are lying down. But because there is not much movement and air flow to stir up particles in our nose, the stimulants do not come in contact with our membranes. We continue sleeping without any disturbance. You won’t sneeze even if these are your worst allergy days. The brain needs stimulation in order to trigger a sneeze reflex. So, during sleep, our brain section that is responsible for sending sneeze signals to the body become inactive. Still, if you need to sneeze while you are asleep, you will have to wake up first and then sneeze.

In addition to these, there are certain external factors which prevent us from sneezing during sleep. While we are in bed, we are not exposed to as many irritants which make us sneeze. There may not be as many pets around and there shouldn't be the kind of irritants which make us sneeze in the places we sleep. And if we sneeze due to photic sneeze reflex, we are probably sleeping in a dark room and we are not exposed to bright lights like sun. Sunlight can also help us wake earlier, helping us to keep a healthy sleep cycle^[1] and help reduce the chance of sneezing due to poor immunity.

Basically, there are two stages of sleep, REM and non-REM. REM stands for Rapid Eye Movement, and REM sleep makes up around 20-25% of our night’s sleep. This is the stage when we dream the most. Our eyes move around under the eye lids and the brain waves are similar to the time when we are awake. Non-REM sleep is a deeper, more peaceful stage of our sleep. Let’s see what happens during these two stages of sleep:

• During non-REM stage of sleep, the cerebral cortex and thalamus in our brain activate one another to keep everything quiet and block all sensory input. Although things are not blocked completely, it becomes tougher for the stimuli to reach the brain. If the stimulus is strong enough, it may pierce through that state of stupor and we wake up. If we sneeze while asleep, it is because an external stimulus caused sneezing and we have to wake up first to sneeze.

• On the other hand, REM sleep prevents sneezing in a different manner. While we are dreaming, our brain puts our body on a lockdown and keeps us from actually doing what we are dreaming of. While sneeze is a strong and coordinated activity of the muscles, some muscles may get paralyzed and it becomes impossible to sneeze.

Now that you have understood the mechanism of sneezing and that it is impossible to sneeze while we are asleep, another important question raised is why do we sneeze in succession. Often we can sneeze 2, 3, 4 or more times in a row. The reason for this may be because the irritant did not clear from the nose in just one sneeze and it had to repeat itself in order to remove the irritant completely from the nose. A person suffering from a cold usually sneezes only once, but those suffering an allergic reaction might be more likely to sneeze several times in a row.

20-35% of people are affected with photic sneezing reflex, who tend to sneeze when they look directly into a strong light source. There is a nerve near your optic nerve, known as trigeminal nerve, which is responsible for giving motor neuron control and facial expression. When you directly see bright light, like a tube light or the sun, the brain receives signals from the optic nerve to contract the pupils. During this phenomenon, the trigeminal nerve senses an electrical signal and mistakes it to be an irritant inside the nose. The result is a sneeze.

As your eyes are normally closed when sleeping, this shouldn't be much of a factor. Even if you are one of the 10% of humans who are able to sleep with their eyes open^[2], your brain will not be signalling the photic reflex while sleeping.

This article is merely informative, oneHOWTO does not have the authority to prescribe any medical treatments or create a diagnosis. We invite you to visit your doctor if you have any type of condition or pain.

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