Although the subject of ‘sneezing during sleep’ has not been extensively studied, most sleep researchers and neuroscientists agree it is physically impossible for people to sneeze while they are sleeping.
For all intents and purposes, humans should sneeze frequently during the night. Our mucus membranes swell when we lie on our back, stomach, or side; swollen mucus membranes are a common cause of sneezing. However, the body suppresses sneezing impulses through a process known as rapid-eye movement (REM) atonia, which occurs during certain periods of sleep. The neurotransmitters that normally detect allergens and other irritants shut down during REM atonia, thus preventing the involuntary urge to sneeze.
Why Do We Sneeze?
Sneezing, also known as sternutation, refers to the involuntary expulsion of air from the lungs through the nose and mouth. Most sneezes occur due to irritants affecting nasal mucus; sneezing essentially cleans out the nose and throat when these irritants are detected.
The biological process for sneezing is as follows:
- Foreign particles enter the nasal cavity, traveling past the nose hairs before reaching mucus membranes in the nasal passageway.
- These particles trigger the release of histamines, organic compounds that are primarily made up of nitrogen particles
- Histamines irritate nerve endings in the nasal mucus membranes
- The irritation causes signals to be sent to the brain
- The brain redirects the signals to the pharyngeal and tracheal muscles, which create larger openings in the nose and throat
- The sneeze occurs
Sneezing utilizes muscles and muscle groups throughout the body. Common causes for sneezing include:
- Allergens, such as dust and pollen
- Non-allergen particles that still irritate the nasal cavity
- Illnesses, such as influenza and the common cold
- Sudden exposure to bright light, such as leaving a darkened building and walking outside during the day; this phenomenon is known as the photic sneeze reflex, and it affects up to 35% of the population
- Snatiation, a relatively rare genetic disorder that triggers sneezing during digestion after filling meals.
Sneezing is rarely dangerous. However, the expulsion can produce up to 40,000 aerosol droplets that can spread infectious diseases. For this reason, physicians urge people to cover their mouths and nose when sneezing, and to wash their hands with soap and water after the sneezing has subsided.
What Is REM Atonia and How Does It Affect Sneezing?
Sleep in humans is facilitated through an internal timekeeper known as the circadian clock. The circadian clock is based on natural sunlight. A sleep-inducing hormone called melatonin is released at night once the sun goes down; then, in the morning, the melatonin tapers off and the sleeper feels more alert.
Following the circadian rhythm, the sleep cycle in humans is composed of five distinct stages: four stages of non-REM sleep (75% of the cycle) and one stage of REM sleep (25% of the cycle).
- Stage 1 is characterized by light, easily disrupted sleep. The eyes move slowly and muscle activity is reduced, although some sleepers experience sudden muscle contractions.
- During Stage 2, eye movement completely ceases and the brain waves become slower. Body temperature decreases and the heart rate slows as the body prepares for deep sleep.
- As the body enters Stage 3, delta waves — slow-moving brainwaves — are interspersed with rapid brain waves. This dynamic causes deep sleep to begin, and represents the transition between non-REM and REM sleep. Parasomnias, such as sleepwalking and bedwetting, are most likely to occur during this stage.
- In Stage 4, the delta waves take over completely; this is also known as slow wave sleep. Waking during Stage 4 can lead to heavy disorientation.
- Stage 5, also known as REM sleep, occurs as the brainwaves begin mimicking responses to waking activities. The eyelids remain closed but the eyes dart quickly from side-to-side. The bulk of dreaming takes place during Stage 5.
The first five-stage cycle lasts roughly 90 minutes, and successive cycles last 100 to 120 minutes. As a result, humans may experience anywhere from four to seven sleep cycles per night.
As we discussed earlier, REM atonia — which exclusively occurs during Stage 5 — causes all neurotransmitters to shut down. As a result, the motor neurons that trigger sneezing are not stimulated, regardless of whether or not the sleeper’s nasal cavity is exposed to irritant particles.
If REM atonia prevents sneezing during Stage 5, then why don’t we sneeze during the other four stages of the sleep cycle? This is where the science gets tricky. In the non-REM stages, two parts of the brain — the thalamus and cerebral cortex — activate one another in order to suppress sensory reactions such as sneezing. However, excessively strong stimuli can still trigger sneezing responses. When this occurs, the sleeper will wake up and then sneeze. So while we do not sneeze while sleeping, we are still susceptible to the sneeze reflex during the non-REM stages and may wake up as a result.
How to Prevent Sneeze Reflexes During the Night
Sleepers can exercise the following precautions before going to bed in order to curb the need to wake up due to sneezing during the night:
- Keep the bedroom clean and vacuum frequently in order to eradicate dust and other allergen particles
- Never keep clothing on your bed; pollen particles, a common allergen for many, cling to most fabrics
- Avoid reading bound books in bed, as these are often breeding grounds for mold; iPads and e-readers can be better substitutes, although some studies have noted that the blue light these devices emit can negatively affect sleep quality
- Clean pillows regularly ? pillow cases and interior fill can be hotbeds for dust mites; in order to completely eradicate particles, consider freezing your pillow for roughly 12 hours two to four times per month
- If your pet sleeps in bed with you, consider laundering your sheets, blankets, pillowcases and other bedding at least once per week