What goes on when the lights go out
Sleep is complex. Scientists are constantly researching its biological functions, how it plays a role in mental and physical health, and how we can get better-quality sleep.
Sleep is also bit of a mystery.
How we can appear dead to the world yet our bodies and brains are still awake and working? How is it possible to climb a tree while sleepwalking or eat an entire cheesecake in our sleep?
If we’re capable of doing extreme things like that while we’re snoozing, then surely firing off a sneeze is plausible. Isn’t it?
We’ve asked experts to explain the possibility of sneezing in your sleep, including when it can occur, at what sleep stage, and more.
Why do we sneeze?
Sneezing is not a pointless bodily function, it does have a purpose.
It’s how your nose kicks irritants out of the nasal passage. When an irritant enters the nose, the sneeze team sends alerts to the throat, eyes, and mouth to close.
At the same time, your chest muscles contract and compress your lungs while your throat relaxes. Then—achoo!—the air, saliva, and mucus are propelled out of your nose and mouth.
Interruptive as sneezing can be—especially when you’re giving a work presentation or during a heartwarming scene at the movie theater—you should just let it out because trying to hold in a sneeze isn’t a good idea.
If you feel a sneeze coming on, grab a tissue. No warning? Sneeze into your elbow. If you’re infected with a contagious illness like flu or Covid-19, you can easily spread germs to others if you don’t cover your sneeze.
What can make you sneeze?
What your nose sees as a foreign invader—dander from the cute pup you petted on your walk or the scent of the laundry detergent aisle—might not make any sense to you. But anything that irritates or aggravates your nose could cause one random sneeze.
Sometimes, the irritants aren’t cleared on the first sneeze. Instead, you might sneeze over and over as your nose tries to clear away irritants.
Sneezing can be due to these common culprits:
Allergies to pollen, hay fever, mold, pet dander, dust mites, and cockroaches
Nasal sprays
Common cold or the flu
Deviated septum
Nasal polyps
Stepping into the bright light
Dry air
Hormonal changes
Tobacco smoke
Pregnancy
What happens during sleep?
To answer that, it helps to understand what happens to your brain and body while you’re in the land of nod.
When you sleep, your brain goes through sleep stages divided into two phases: non-rapid eye movement (REM) sleep and rapid eye movement (REM) sleep.
Adults spend about 75 percent of the sleep cycle in NREM and 25 percent in REM. But the process isn’t uniform. You could repeat the cycle four to six times during the night.
Stage 1
Non-REM sleep when you’re just starting to doze off. During this short period of relatively light sleep, your heartbeat, brain waves, breathing, and eye movements slow.
As your muscles relax, twitches in your body, like in your foot or hand and fingers, might occur.
Stage 2
This is a period of light, non-REM sleep before you enter deeper sleep. Your heart rate and breathing slow down, and your muscles relax even further.
Brain wave activity slows further, and you’re pretty much unaware of your surrounding. There are still some sudden bursts of brain activity called “sleep spindles.”
Stage 3
This stage is the deep, non-REM sleep we covet and desperately need to feel energized for the day ahead. It occurs in more extended periods during the first half of the night.
Your muscles are relaxed, and your heartbeat and breathing slow to their lowest levels during sleep. Brain waves become even slower.
It’s would be difficult for someone to wake you at this stage. If they do, you’ll feel dazed and confused.
Stage 4
This sleep stage, also called REM, typically occurs about 90 minutes after falling asleep, and it’s when most of your dreaming occurs.
Your mind may be active during this stage, but your arm and leg muscles become temporarily paralyzed.
“We have near-complete muscle atonia—at least in terms of skeletal muscles that help us move about,” says Spencer Dawson, an Indiana-based licensed clinical psychologist who is board certified in behavioral sleep medicine.
This keeps us from acting out our dreams and helps keep us from hurting ourselves or our sleeping partner. (Though some sleep disorders can make it possible. More on that later.)
Brain wave activity is mixed and closer to that of wakeful state. Your heart rate and blood pressure are also near waking levels, while your breathing becomes faster and irregular.
At what stage of sleep does sneezing occur?
You won’t sneeze during REM sleep, even if you’re sneezing in your dreams.
Remember, the body is practically lifeless and unable to move during REM sleep. This is called REM atonia, in which the signals to the motor neurons of the body are cut off.
“Any functions that require movement of the muscles will not happen while our body is ‘paralyzed’ during REM sleep. So the ‘response’ arm in the sneezing reflex will not be triggered while you are in your deepest sleep,” says Katherine Green, MD, medical director of the UCHealth Sleep Medicine Clinic in Aurora, Colorado.
That said, it’s possible to think you sneezed while you slept or to sneeze during lighter sleep stages. Nasal irritation may be enough to wake you up briefly, then you sneeze.
If you quickly go back to sleep, you might think it happened while you were sleeping.
“Brief awakenings are typically not remembered, but that research has not been on awakenings that are as stimulating as sneezing,” says Dawson, who is also an assistant clinical professor and associate director of clinical training in the Department of Psychological and Brain Sciences at Indiana University in Bloomington.
Can someone else’s sneeze wake me up?
It depends on how you perceive a sneeze. “Sensation is the basic physical/physiological process by which light, noise, touch, smell, and taste stimulate nerves, which is basically an automatic response,” says Dawson.
Yet how we actually perceive stimuli while we sleep is altered a bit. For example, familiar noises, such as the furnace or air conditioning, might not fully wake you up.
Your name being called, the sound of your dog about to throw up, or a very loud sneeze may be perceived as more important, causing you to wake up, even if the overall noise level is the same.
Can I smell things in my sleep?
If sneezing is suppressed during sleep, does your sense of smell take a snooze too?
“Smells can be consciously perceived only during lighter sleep stages of sleep,” Dawson says. But the sensation of smell doesn’t go away.
“Researchers have been able to strengthen memories during sleep by pairing a stimulus with a smell while a person is learning, then exposing them to that same smell while asleep,” he says.
Bodily functions that shut down during sleep
Many of our body’s basic actions and triggers are somewhat suppressed during sleep, such as hunger, thirst, urination, and defecation, says Dr. Green.
Still, your brain never sleeps. “If your body has to do any of these things badly enough, your brain will wake you from sleep,” she says.
That’s why you’ll sometimes wake up in the middle of the night to pee.
In some people, there is a loss or reduction of muscle atonia during REM sleep. It’s called REM behavior disorder (RBD), and it means that, unlike most people, you don’t have temporary paralysis of the arms and legs during REM sleep.
“In many cases, people with RBD may injure themselves or their bed partners due to moving about, flailing, or trying to hit someone or something in their dream,” explains Dr. Green.
Other sleep disorders, such as sleepwalking, sleep talking, and night terrors, can be dangerous to you and your bed partner and rob you of valuable snooze time.
Sleep is essential to overall good health. Don’t wait for sleep to get better. See your doctor for a proper diagnosis and treatment.
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