Farting is your body’s way of releasing gas that builds up in your digestive tract. It’s completely normal, and the average healthy person does it about 10 times a day, with anything up to 20 times still falling within the typical range. The gas itself comes from two sources: air you swallow and gases produced by bacteria in your large intestine as they break down food.
Where the Gas Actually Comes From
Every time you eat, drink, or swallow saliva, small amounts of air travel into your stomach. Most of that swallowed air gets burped back up before it goes any further. But some of it continues through the digestive tract and eventually exits as flatulence. The two atmospheric gases in that swallowed air, nitrogen and oxygen, account for a large share of what’s in a fart. Nitrogen alone makes up about 65% of intestinal gas on average.
The rest is manufactured inside you. Trillions of bacteria living in your colon feed on carbohydrates and fiber that your small intestine couldn’t fully absorb. As these bacteria break down those leftovers, they produce hydrogen, carbon dioxide, and in some people, methane. Carbon dioxide makes up roughly 10% of flatus, methane about 14%, and hydrogen around 3%. Together with nitrogen and a tiny amount of oxygen, these five gases account for over 99% of what you pass.
Here’s something surprising: most of the hydrogen and methane your gut bacteria produce never makes it out as a fart. Only about 10% of hydrogen is actually expelled rectally. The rest gets absorbed through your intestinal wall into your bloodstream, carried to your lungs, and quietly exhaled. Your body is constantly venting digestive gases through your breath without you ever noticing.
Why Some Farts Smell and Others Don’t
The five main gases in flatulence are all odorless. The smell comes from trace sulfur-containing compounds, particularly hydrogen sulfide (the classic rotten-egg gas), methyl mercaptan, and dimethyl sulfide. These make up less than 1% of the total gas volume, but your nose is extraordinarily sensitive to them even in tiny concentrations.
Foods rich in sulfur-containing amino acids tend to produce smellier gas. Think eggs, meat, cruciferous vegetables like broccoli, cauliflower, and cabbage, and alliums like garlic and onions. If your diet is heavy on these foods, the bacteria in your colon have more sulfur compounds to work with, and the result is more pungent.
Foods That Make You Gassy
Certain carbohydrates are poorly absorbed in the small intestine, which means they arrive in the colon mostly intact and become a feast for gas-producing bacteria. Nutritional scientists group these into a category called FODMAPs, short-chain carbohydrates found in a wide range of everyday foods. In controlled studies, people on a high-FODMAP diet produced roughly four times the intestinal hydrogen compared to those on a low-FODMAP diet.
The most common culprits include:
- Beans and lentils, which contain complex sugars your body lacks the enzyme to break down on its own
- Dairy products, especially if you’re lactose intolerant
- Wheat, onions, and garlic, which contain fructans
- Apples, pears, and stone fruits, which are high in fructose and sorbitol
- Cruciferous vegetables like broccoli, Brussels sprouts, and cabbage
Lactose intolerance is one of the most common specific triggers. When your body doesn’t produce enough of the enzyme that breaks down lactose (the sugar in milk), that lactose passes through to the colon, where bacteria ferment it rapidly. The result is a surge of carbon dioxide, hydrogen, and methane, along with bloating and sometimes diarrhea.
Swallowed Air Adds Up
Diet isn’t the only factor. You might be swallowing more air than you realize through everyday habits: eating too quickly, talking while you eat, chewing gum, sucking on hard candy, drinking through straws, or sipping carbonated drinks. Smoking also increases the amount of air you swallow.
Some medical situations make the problem worse. Poorly fitting dentures cause your mouth to produce extra saliva, and you swallow more often as a result. Stress and anxiety can create a nervous swallowing pattern. People who use CPAP machines for sleep apnea sometimes swallow excess air from the pressurized flow. In extreme cases, a condition called aerophagia can cause people to belch up to 120 times an hour and pass gas well beyond the normal range.
What “Too Much” Gas Looks Like
Passing gas up to 20 times a day is within the normal range for healthy adults. Beyond that, you’re likely dealing with either dietary triggers, excess air swallowing, or an underlying digestive issue. The gas itself isn’t the concern. What matters is whether it comes with other symptoms.
A sudden change in your gas patterns, especially alongside abdominal pain, persistent bloating, diarrhea, constipation, or unexplained weight loss, can point to conditions worth investigating. These include irritable bowel syndrome, celiac disease, small intestinal bacterial overgrowth (where too many bacteria colonize your small intestine and produce extra gas), and food intolerances beyond lactose, such as fructose intolerance.
In rarer cases, persistent digestive symptoms including excess gas can be associated with more serious conditions like gastroparesis (delayed stomach emptying) or even intestinal obstruction. The gas alone isn’t the red flag. It’s the combination of gas with pain, changes in bowel habits, or weight loss that warrants attention.
Your Gut Bacteria Make You Unique
Not everyone produces the same types of gas. Only a portion of the population has significant levels of methane-producing microbes (called methanogens) in their gut. Research shows that people with higher methanogen levels tend to have a more diverse gut microbiome overall. Their bacterial communities look measurably different from those of people who produce little methane. This is why two people can eat the exact same meal and have completely different gas experiences.
The bacteria in your colon also interact with each other. Some species consume the hydrogen that others produce, converting it into methane or other byproducts. This internal recycling means your gut ecosystem is constantly adjusting how much gas actually accumulates and needs to be released.
Reducing Gas Practically
If gas is bothering you, start with the simplest fixes. Slow down when you eat, skip the gum and straws, and cut back on carbonated drinks. These changes reduce the swallowed-air component, which can make a noticeable difference on its own.
For gas caused by specific foods, over-the-counter enzyme supplements can help. One well-studied option is alpha-galactosidase, an enzyme that breaks down the complex sugars in beans and certain vegetables before they reach your colon. In a randomized, placebo-controlled trial, it significantly reduced bloating and flatulence with no reported side effects. Lactase supplements work on the same principle for people with lactose intolerance, providing the missing enzyme before you consume dairy.
A low-FODMAP diet, ideally guided by a dietitian, is one of the most effective approaches for people with IBS or chronic gas. In studies, reducing FODMAP intake cut intestinal hydrogen production by roughly 75% in both healthy people and IBS patients. The diet works in phases: you eliminate high-FODMAP foods, then reintroduce them one at a time to identify your personal triggers rather than avoiding everything permanently.