Most Likely Causes (Ranked)
Foods high in sulfur (eggs, broccoli, cauliflower, cabbage, garlic, onions, red meat, beer, wine) are broken down by gut bacteria into hydrogen sulfide and methanethiol — potent rotten-egg smelling gases.
Lactose intolerance, fructose malabsorption, and gluten sensitivity cause undigested food to ferment in the colon, producing excess smelly gas. About 65% of adults have some degree of lactose intolerance.
Eating quickly, chewing gum, drinking carbonated beverages, and using straws increases swallowed air. While swallowed air itself is odorless, it changes gut transit time and fermentation patterns.
Antibiotics, illness, travel, or sudden dietary changes disrupt the balance of gut bacteria. Some bacterial strains produce more sulfur compounds than others.
SIBO (small intestinal bacterial overgrowth), IBS, Crohn's disease, celiac disease, or pancreatic insufficiency can all cause excessive, foul-smelling gas as part of broader digestive dysfunction.
How to Fix It
Adjust Diet
$0Works for most people within days.
- 1Reduce top sulfur foods for 1 week: eggs, broccoli, cauliflower, cabbage, garlic, onions, red meat.
- 2Add foods gradually back one at a time to identify your specific triggers.
- 3Eat slowly and chew thoroughly — less air swallowed, better initial digestion.
- 4Soak beans overnight before cooking — removes some of the gas-producing oligosaccharides.
Support Gut Health
$0-30Optimizes the bacterial balance.
- 1Take a daily probiotic — strains like Lactobacillus and Bifidobacterium can reduce gas and improve odor.
- 2Increase soluble fiber gradually (oats, psyllium) — feeds beneficial bacteria that produce less sulfur.
- 3Consider digestive enzymes (Beano for beans, lactase for dairy) taken before meals.
- 4Drink peppermint tea — relaxes gut muscles and can reduce bloating and gas.
See a Doctor
$50-300For persistent issues with other symptoms.
- 1Hydrogen breath test can identify lactose intolerance or SIBO.
- 2Celiac blood test (tTG-IgA) if gluten is a suspected trigger.
- 3Stool tests for infections or fat malabsorption.
- 4Most digestive conditions causing excess gas are very treatable.
When to Call a Professional
Gas with persistent diarrhea or constipation — may indicate IBS, IBD, or food intolerance.
Gas with significant bloating and abdominal pain — could be SIBO or other digestive condition.
Unintentional weight loss with gas changes — warrants medical evaluation.
Gas that starts after antibiotics and doesn't resolve — possible C. diff or persistent dysbiosis.
How to Prevent It
Eat slowly and chew well.
Identify your personal trigger foods and moderate intake.
Stay active — exercise promotes healthy gut motility.
Take probiotics regularly.
Cook vegetables well — cooking breaks down some gas-producing compounds.
Only 1% of Your Fart Actually Smells
The average fart is about 59% nitrogen, 21% hydrogen, 9% carbon dioxide, 7% methane, and 4% oxygen — all completely odorless. It's the remaining fraction of a percent — trace sulfur compounds like hydrogen sulfide, methanethiol, and dimethyl sulfide — that your nose detects.
Your nose can detect hydrogen sulfide at concentrations as low as 0.5 parts per billion, which is why even tiny amounts create a noticeable smell. This is actually a survival adaptation — hydrogen sulfide is toxic at high concentrations, so humans evolved extreme sensitivity to it.
Frequently Asked Questions
Yes. The average person farts 14-23 times per day. Most are small and odorless. Excessive gas (more than 25+ times daily) or very smelly gas may indicate a dietary issue or food intolerance.
Yes, for many people. Probiotics can rebalance gut bacteria to favor strains that produce less sulfur. Results typically take 2-4 weeks of consistent use. Look for multi-strain formulas with Lactobacillus and Bifidobacterium.
Food eaten during the day has had time to reach the colon where bacterial fermentation occurs. Evening gas represents the day's dietary choices. Also, lying down can release gas that accumulated during the day.
No. Held gas is eventually reabsorbed or released gradually. There's no medical evidence that holding gas causes harm, though it may cause temporary bloating or discomfort.