Why Do You Fart in Your Sleep? The Science of Nighttime Gas

Written by the Nuvirox Research Team

Short answer: yes, and it’s a completely normal side effect of how your anal sphincter behaves during sleep, not a sign anything is wrong. Digestion doesn’t pause when you close your eyes. Gut bacteria keep breaking down food residue in your colon around the clock, generating the same nitrogen, carbon dioxide, hydrogen, and occasionally methane that account for gas during the day. What changes at night is the muscular gatekeeping.

What actually relaxes while you sleep?

The clearest data on this comes from a classic manometry study that measured pressure inside the anal canal continuously while healthy subjects fasted, ate, and slept. Researchers found that average anal canal pressure was similar across all three states, but the pattern of pressure changed: propagating colonic contractions were sharply suppressed during slow-wave sleep and essentially eliminated during deep sleep, then picked back up during REM sleep and waking (Orkin BA, Hanson RB, Kelly KA, Phillips SF, John D. Human anal motility while fasting, after feeding, and during sleep. Gastroenterology. 1991;100:1016-23. PMID 2001798.). The practical translation is that the sphincter isn’t simply "off" at night — it fluctuates with sleep stage, and phases of lighter sleep and REM appear to be when gas is most likely to pass.

Why don't I usually wake myself up?

Two things line up in your favor. First, the pressure changes involved are typically small and gradual rather than sudden. Second, your sense of smell becomes measurably less sensitive during non-REM sleep — the arousal threshold for odors rises, so mild-to-moderate smells often don’t register strongly enough to wake a sleeping brain. That combination is also why a bed partner is sometimes more aware of nighttime flatulence than the person producing it: their own arousal threshold and sleep stage at that exact moment determine whether they notice, which is part of why it can feel inconsistent from night to night even with an unchanged diet.

What Human Research Actually Shows

Orkin et al., Gastroenterology, 1991. In 19 healthy subjects, continuous anorectal manometry over 8 hours of sleep documented that while average pressure was similar to waking levels, propagating colonic contractions and phasic sphincter changes were markedly reduced during slow-wave sleep and increased again with REM sleep and arousals (Orkin BA, Hanson RB, Kelly KA, Phillips SF, John D. Human anal motility while fasting, after feeding, and during sleep. Gastroenterology. 1991;100:1016-23. PMID 2001798.). This remains one of the only controlled physiological studies directly measuring what the sphincter does overnight, rather than relying on self-report.

Honest counterweight. There is very little rigorous research specifically on nighttime flatulence frequency or what predicts it — most of what circulates online about "13 to 21 times a day" figures traces back to general daytime gas-production estimates, not sleep-specific counts. We haven’t found a controlled study that directly counted overnight flatus episodes with objective measurement, so claims about exact nighttime frequency should be read as reasonable inference from the manometry data above, not a directly measured statistic.

What This Doesn't Explain — and When to See a Doctor

For the overwhelming majority of people, this is not a medical issue and doesn’t need treatment. It becomes worth mentioning to a doctor if it’s accompanied by abdominal pain, noticeable bloating, diarrhea, blood in stool, unintended weight loss, or a fairly sudden and sustained increase in frequency — those combinations can point toward lactose intolerance, small intestinal bacterial overgrowth, or other digestive conditions that are worth ruling out, rather than nighttime gas being the problem in itself.

What actually changes how much gas you produce

Diet is the biggest lever: beans, cruciferous vegetables, onions, carbonated drinks, and sugar alcohols (found in some "sugar-free" products) are common contributors because they reach the colon partly undigested, where bacteria ferment them into gas. Eating your last meal earlier, chewing more slowly (less swallowed air), and identifying your own trigger foods through a short elimination trial tend to help more than anything targeted at sleep itself.

Frequently Asked Questions

Is it worse for people who sleep on their side?

There's plausible anatomical logic — side-sleeping can change how gas pools and moves through the colon — but this hasn't been rigorously tested in controlled studies, so treat it as a reasonable theory rather than an established fact.

Does everyone do this, or is it more common in some people?

The physiological mechanism (intermittent sphincter relaxation during sleep) appears to be universal human physiology, though how much gas any individual produces depends heavily on diet and gut microbiome composition, which varies a lot person to person.

Could this be a sign of a food intolerance?

It can be one clue among several. If nighttime gas is new, frequent, and paired with bloating or discomfort — especially after dairy — it's worth considering lactose intolerance or another digestive cause and mentioning it to a doctor rather than assuming it's just normal variation.

Does it affect sleep quality?

Not directly, for most people — the process itself doesn't typically cause arousal. If bloating or cramping accompanies it, however, that discomfort can disrupt sleep, which is a separate issue from the gas passage itself.

Does everyone produce the same amount of gas, or does it vary a lot?

It varies substantially based on diet, gut microbiome composition, and how much air a person tends to swallow while eating or talking. Two people eating identical meals can produce noticeably different amounts of gas because the bacterial populations fermenting that food in each person's colon aren't the same.

FROM NUVIROX

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The Bottom Line

Nighttime flatulence is an ordinary consequence of how the anal sphincter behaves across sleep stages, not a symptom to worry about on its own. It’s one of several involuntary processes the body runs overnight without your input — alongside things like nighttime muscle clenching, which follows a very different but equally automatic mechanism. If bloating is part of your nightly pattern, our piece on why you feel bloated after a bad night of sleep digs into the gut-sleep relationship in more depth, and if dairy seems to be a trigger, see how lactose intolerance disrupts sleep.

References

1. Orkin BA, Hanson RB, Kelly KA, Phillips SF, John D. Human anal motility while fasting, after feeding, and during sleep. Gastroenterology. 1991;100:1016-23. PMID 2001798.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.