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What is a pass gass? Why do farts smell?
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"Pass gas" (also called flatulence, passing wind, or farting) is the release of gas from your digestive tract through the rectum. Gas in the gut comes from two main sources:
- air you swallow (when you eat, drink, talk, or chew gum), and
- gases produced by bacteria in your large intestine as they break down undigested food (fermentation).
What gas is made of
Most intestinal gas is odorless and contains nitrogen, oxygen, carbon dioxide, hydrogen and sometimes methane. Only a small fraction of the gas contains smelly chemicals, but those are potent enough to make farts smell.
Why farts smell
Smell comes mainly from sulfur-containing compounds and other volatile organic compounds produced by gut bacteria when they digest certain foods or proteins. Common smelly compounds include:
- hydrogen sulfide (rotten-egg smell),
- methanethiol and dimethyl sulfide,
- indole and skatole (fecal, pungent odors),
- ammonia.
Factors that make gas smellier
- Diet: sulfur-rich foods (eggs, meat, onions, garlic, broccoli, cabbage, Brussels sprouts), high-protein meals, and some carbohydrates that ferment (beans, lentils) can increase smelly gases.
- Food intolerances/malabsorption: lactose intolerance, fructose malabsorption, or pancreatic insufficiency can leave food for bacteria to over-ferment.
- Gut microbiome: different bacterial communities produce different gases.
- Slow transit or constipation: allows more time for bacteria to produce smelly compounds.
- Certain medications or supplements can alter smell.
Is it normal?
Yes. Passing gas is a normal bodily function; many healthy people pass gas 10–20 times per day. It becomes a concern if it’s accompanied by severe abdominal pain, bleeding, unintentional weight loss, persistent diarrhea or constipation, fever, or sudden major changes — in those cases see a clinician.
How to reduce smelly gas
- Identify and limit trigger foods (especially sulfurous foods and fermentable carbs).
- Try alpha-galactosidase (Beano) for gas from beans/oligosaccharides.
- If lactose might be the issue, try lactose-free products or lactase supplements.
- Eat slowly to reduce swallowed air.
- Consider a low-FODMAP diet if you have IBS (work with a dietitian).
- Treat underlying problems (SIBO, infections, etc.) if diagnosed.
If you want, tell me what you’re eating and any other symptoms and I can suggest likely causes and next steps.
- air you swallow (when you eat, drink, talk, or chew gum), and
- gases produced by bacteria in your large intestine as they break down undigested food (fermentation).
What gas is made of
Most intestinal gas is odorless and contains nitrogen, oxygen, carbon dioxide, hydrogen and sometimes methane. Only a small fraction of the gas contains smelly chemicals, but those are potent enough to make farts smell.
Why farts smell
Smell comes mainly from sulfur-containing compounds and other volatile organic compounds produced by gut bacteria when they digest certain foods or proteins. Common smelly compounds include:
- hydrogen sulfide (rotten-egg smell),
- methanethiol and dimethyl sulfide,
- indole and skatole (fecal, pungent odors),
- ammonia.
Factors that make gas smellier
- Diet: sulfur-rich foods (eggs, meat, onions, garlic, broccoli, cabbage, Brussels sprouts), high-protein meals, and some carbohydrates that ferment (beans, lentils) can increase smelly gases.
- Food intolerances/malabsorption: lactose intolerance, fructose malabsorption, or pancreatic insufficiency can leave food for bacteria to over-ferment.
- Gut microbiome: different bacterial communities produce different gases.
- Slow transit or constipation: allows more time for bacteria to produce smelly compounds.
- Certain medications or supplements can alter smell.
Is it normal?
Yes. Passing gas is a normal bodily function; many healthy people pass gas 10–20 times per day. It becomes a concern if it’s accompanied by severe abdominal pain, bleeding, unintentional weight loss, persistent diarrhea or constipation, fever, or sudden major changes — in those cases see a clinician.
How to reduce smelly gas
- Identify and limit trigger foods (especially sulfurous foods and fermentable carbs).
- Try alpha-galactosidase (Beano) for gas from beans/oligosaccharides.
- If lactose might be the issue, try lactose-free products or lactase supplements.
- Eat slowly to reduce swallowed air.
- Consider a low-FODMAP diet if you have IBS (work with a dietitian).
- Treat underlying problems (SIBO, infections, etc.) if diagnosed.
If you want, tell me what you’re eating and any other symptoms and I can suggest likely causes and next steps.
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