Do humans release methane when they fart? The surprising science of flatulence

September 26, 2025 •

4 min read

While all humans pass gas, studies show that only about one-third to half of the population actually produces methane. So, do humans release methane when they fart? For those with specific microorganisms in their gut, the answer is a definitive yes.

Quick Summary

A portion of the human population releases methane in their flatulence, a byproduct of specialized microorganisms called archaea in the gut microbiome. The composition of intestinal gas varies significantly between individuals.

Key Points

Methane isn't universal: Only about 30-50% of the human population produces methane in their flatulence.
The source is archaea: Methane is created by methanogenic archaea in the large intestine, which consume hydrogen produced by other gut bacteria.
Genetics matter: Whether you produce methane is largely influenced by your genetics and is a familial trait.
Methane is odorless: Contrary to popular belief, methane is an odorless gas. The smell of farts comes from other trace compounds, particularly those containing sulfur.
High levels can impact health: High methane production can slow intestinal transit and has been linked to constipation and IBS-C in some individuals.
Diet plays a role: The amount of methane produced can be influenced by diet, specifically the intake of certain fermentable carbohydrates that feed the gut microbes.

The composition of human flatulence

Human flatulence is not a single type of gas but a complex mixture of vapors. Most of the volume consists of odorless gases, primarily nitrogen and carbon dioxide, which make up over 99% of the gas in healthy individuals. Other gases, like hydrogen and sometimes methane, are produced by the gut's microbial inhabitants. The unpleasant odor associated with farts comes from trace amounts of sulfur-containing gases, such as hydrogen sulfide, which are also produced by bacteria.

The two sources of intestinal gas

Intestinal gas comes from two main sources:

Swallowed air (Aerophagia): Everyone swallows air when eating and drinking. Swallowed air that isn't released through burping travels down to the intestines. This air consists mostly of nitrogen and oxygen.
Microbial fermentation: In the large intestine, trillions of microbes break down undigested carbohydrates. This fermentation process releases various gases, including hydrogen, carbon dioxide, and, for some, methane.

Are all humans methane producers?

No, not all humans are methane producers. The production of methane in the human gut is not universal and depends on the presence of a specific type of microorganism called archaea. Approximately 30-50% of the adult population worldwide is considered a methane producer. The presence of these archaea is largely determined by factors like genetics, age, and dietary habits.

The role of methanogenic archaea

Methanogenic archaea, particularly a species known as Methanobrevibacter smithii, are the only organisms in the human gut capable of producing methane. These microorganisms are not bacteria but belong to a separate domain of life. Their metabolism is unique: they consume the hydrogen and carbon dioxide produced by other gut bacteria during fermentation and convert it into methane.

Why some produce methane and others don't

Genetics and inheritance: The propensity to host methanogenic archaea seems to be a familial trait. Children of two methane-producing parents have a very high chance (around 95%) of also being methane producers. This suggests that genetic factors play a significant role in determining gut colonization.
Dietary factors: Diet can influence the amount of methane produced. A diet rich in fermentable fibers promotes the growth of hydrogen-producing bacteria. Methanogens then use this excess hydrogen to create methane. Studies have also shown links between high vitamin B12 intake and lower methane production.
Microbial balance: The ecosystem of the gut microbiome is complex. A specific balance between different microbial groups (methanogens, hydrogen-producing bacteria, sulfate-reducing bacteria) determines the final gas composition.

Methane production and its health implications

While methane production is a normal bodily function for many, high levels of methane have been linked to certain health conditions, particularly constipation. Research has shown that methane can have a direct effect on intestinal motility, slowing down the transit of waste through the gut. This can exacerbate symptoms for individuals with constipation-predominant irritable bowel syndrome (IBS-C).

However, it's important to note that methane production is not inherently harmful. For some, it might even be beneficial, as methanogens can help regulate hydrogen levels in the gut, making fermentation more efficient. The issue arises when there is an overgrowth or imbalance of these microorganisms, a condition known as Intestinal Methanogen Overgrowth (IMO).

Comparison of intestinal gases


Gas	Source	Producer	Effects	Presence in Farts
Nitrogen	Swallowed air	N/A	Odorless	Very high
Oxygen	Swallowed air	N/A	Odorless	High
Carbon Dioxide	Swallowed air & microbial fermentation	Various gut bacteria	Odorless	High
Hydrogen	Microbial fermentation	Various gut bacteria	Odorless; flammable	Varies
Methane	Microbial fermentation	Methanogenic archaea	Odorless; flammable; slows motility	Varies (only in methane producers)
Hydrogen Sulfide	Microbial fermentation	Sulfate-reducing bacteria	Odor (rotten eggs)	Low, trace amounts

Can your diet reduce methane in farts?

For those who are methane producers, dietary changes can potentially influence the amount of methane produced. Since methanogens feed on the byproducts of carbohydrate fermentation, reducing the intake of certain fermentable carbohydrates can lower methane output. These include foods high in raffinose, fructose, and sorbitol, such as beans, cabbage, and some sugar-free products.

High-fiber foods: Foods like beans, broccoli, and Brussels sprouts contain complex carbohydrates that are not easily digested in the small intestine. When these reach the large intestine, the gut microbes ferment them, producing gas.
FODMAPs: Certain fermentable carbohydrates known as FODMAPs can lead to increased gas production in sensitive individuals. A low-FODMAP diet is sometimes recommended to help manage symptoms associated with gas and bloating.
Probiotics and enzymes: Over-the-counter products containing digestive enzymes can help break down carbohydrates before they reach the large intestine, reducing the amount of gas produced by fermentation.

Conclusion

To definitively answer the question, do humans release methane when they fart, the answer is some do, but not all. The presence of methane is determined by the specific composition of a person's gut microbiome, particularly the presence of methanogenic archaea. This is a normal physiological process, and methane itself is odorless, contributing to the volume of gas rather than the smell. While high methane production has been linked to conditions like constipation, it is the result of a normal symbiotic relationship between the host and their gut microbes. Understanding the factors that influence gas composition—from diet to genetics—can provide valuable insights into individual digestive health and offer strategies for managing related symptoms. More research continues to shed light on the complex relationship between our gut flora and overall well-being, as detailed in extensive studies like this review on intestinal gas metabolism: Methanogens, Methane and Gastrointestinal Motility.

Frequently Asked Questions

The primary gases in human flatulence are typically odorless and come from swallowed air and fermentation. These include nitrogen, carbon dioxide, and hydrogen. Methane is present only in about half the population.

Methane is produced by a special type of microorganism called methanogenic archaea, primarily Methanobrevibacter smithii, which lives in the large intestine of some individuals. These archaea consume hydrogen and convert it to methane.

No, methane is an odorless gas. The foul smell in farts is caused by trace amounts of sulfur-containing gases, such as hydrogen sulfide, which are produced by different types of bacteria in the gut.

Yes, diet plays a significant role. Consuming foods high in fermentable carbohydrates, such as beans and certain vegetables, can increase the activity of the gut microbes that produce the hydrogen methanogens consume, thereby increasing methane output.

While methane production is often normal, studies have linked high levels of methane to certain issues. For some, it may slow intestinal transit, which can be associated with symptoms of chronic constipation or constipation-predominant irritable bowel syndrome (IBS-C).

The signature smell of flatulence is caused by trace volatile sulfur compounds produced by bacteria. While odorless gases like methane make up the bulk of the gas, it only takes a small amount of sulfur-rich gas to create a strong odor.

There is no definitive evidence to suggest one is healthier than the other. Some studies indicate that moderate methane production can help regulate the gut ecosystem, while excessive methane has been linked to constipation in some people. It simply reflects the unique microbial balance of an individual's gut.