Passing Gas (Flatulence)

What is normal?

Healthy adults pass gas an average of 10 to 20 times a day, with some normal people passing it more than 20 times. Gas production rises after meals and in the evening. Intestinal gas is mostly odorless nitrogen, oxygen, carbon dioxide, hydrogen and, in some people, methane. The smell comes from tiny amounts of sulfur compounds such as hydrogen sulfide.

People who feel they have "too much gas" often produce a normal volume but are more sensitive to it, as in irritable bowel syndrome.

Where intestinal gas comes from

Swallowed air

Everyone swallows some air. More air is swallowed when you:

• eat or drink quickly
• chew gum or suck hard candy
• drink through a straw or drink fizzy drinks
• smoke
• have loose dentures
• are anxious and breathe quickly

Most swallowed air is burped up (belching), but some travels through the intestines.

Bacterial fermentation

The large intestine hosts trillions of bacteria. When carbohydrates reach them undigested, they ferment, producing hydrogen, carbon dioxide and methane. The main culprits:

What makes gas smell worse

Sulfur-rich foods (eggs, meat, cruciferous vegetables, garlic, onions), some supplements, constipation and certain gut infections produce more hydrogen sulfide.

Medical causes of excessive gas

• Lactose intolerance: gas, bloating, cramps and loose stools 30 minutes to 2 hours after dairy.
• Irritable bowel syndrome (IBS): gas, bloating, belly pain relieved by a bowel movement, and diarrhea, constipation or both.
• Constipation: stool sitting in the colon ferments longer, producing more and smellier gas.
• Celiac disease: an immune reaction to gluten that damages the small intestine, causing gas, bloating, diarrhea, weight loss and anemia.
• Small intestinal bacterial overgrowth (SIBO): bacteria in the small intestine ferment food early, causing bloating and gas soon after meals.
• Fructose malabsorption.
• Infections: giardia causes foul-smelling gas, sulfur burps and greasy diarrhea.
• Medicines and supplements: metformin, acarbose, orlistat, fiber supplements, lactulose, and some GLP-1 medicines.
• Pancreatic insufficiency: poor fat digestion with pale, greasy, foul-smelling stools.

Gas with other symptoms

• Gas and bloating with a visibly swollen belly by evening: IBS, constipation or food intolerance.
• Gas with burping and heartburn: air swallowing or reflux.
• Gas with diarrhea after dairy: lactose intolerance.
• Gas with weight loss and loose stools: celiac disease, SIBO, pancreatic or inflammatory bowel disease. See a doctor.
• Sharp gas pains: trapped gas can cause sharp, moving pains that ease once it passes. Pain that is constant or severe is not just gas.

How doctors find the cause

A doctor will ask about diet, bowel habits and other symptoms, and examine your belly. A 1 to 2 week food and symptom diary is often the most useful tool. Tests are used when symptoms suggest an underlying condition:

• blood tests for celiac disease and anemia
• hydrogen breath tests for lactose or fructose malabsorption and SIBO
• stool tests for infections such as giardia, and for inflammation
• colonoscopy if there are red flags or you are due for bowel cancer screening

How to reduce gas

Diet

• Find your triggers: cut back on one suspected food group at a time for 2 weeks and see what changes.
• Introduce fiber gradually over several weeks so gut bacteria adapt.
• Soak and rinse beans, or use canned beans, which produce less gas.
• Try lactose-free dairy or lactase enzyme tablets with dairy.
• Avoid sugar alcohols in sugar-free products.
• A low-FODMAP diet, done with a dietitian for a few weeks and then gradually relaxed, helps many people with IBS.

Habits

• Eat slowly with your mouth closed, and avoid gum, straws and fizzy drinks.
• Stay active. A walk after meals helps move gas through.
• Treat constipation with fluids, fiber and regular routines.

Over-the-counter options

• Simethicone may help gas bubbles combine and pass, though evidence is mixed.
• Alpha-galactosidase (taken with the first bite of beans or vegetables) breaks down the sugars in legumes.
• Lactase for dairy.
• Activated charcoal and charcoal-lined underwear can reduce odor. Charcoal can interfere with medicines, so check with a pharmacist.
• Probiotics help some people, but results vary.

Frequently asked questions

How many times a day is it normal to pass gas?

Most healthy people pass gas about 10 to 20 times a day, and up to 25 can still be normal. It increases after meals and with a high-fiber diet. Frequency matters less than whether it comes with pain, diarrhea, weight loss or other symptoms.

Why do I fart so much?

The most common reasons are eating foods that ferment in the gut, such as beans, onions, wheat, cruciferous vegetables, dairy if you are lactose intolerant, and sugar-free sweets, and swallowing air. Constipation, IBS and some medicines also increase gas. A food diary helps identify your triggers.

What causes very smelly gas?

Smell comes from sulfur compounds produced when gut bacteria break down sulfur-rich foods such as eggs, meat, garlic, onions and broccoli. Constipation and some gut infections, like giardia, make it worse. Foul gas with greasy diarrhea or weight loss should be checked.

Is passing a lot of gas a sign of something serious?

Usually not. Excess gas is most often diet-related. It is more concerning when it comes with unexplained weight loss, blood in the stool, persistent diarrhea, anemia, or a change in bowel habits after 50. These need medical assessment.

What is the fastest way to relieve trapped gas?

Walk around, gently massage your belly in a clockwise direction, or lie on your left side or in a knees-to-chest position. A warm drink or heating pad can ease cramping. Over-the-counter simethicone may help some people.