What is Flatus? Natural Human Gas from Colon, Bowel

Flatus Definition

Flatus is the gas that is passed out of the gut through the anus. It is commonly referred to as a ‘fart’. Expelling gas from the gut is a normal physiological process, whether through the mouth as a belch (‘burp’), or through the anus as flatus. Approximately 600 to 700 milliliters of gas is passed out in a day with less than 200 ml remaining in the gut.

Flatus as a Diagnosis

The act of passing out flatus is known as flatulence. It is accepted as a part of everyday life unless it becomes excessive, unusually loud, extremely offensive odor or accompanied by other gastrointestinal symptoms like fecal incontinence, diarrhea, constipation or pain.

Flatulence can vary from being almost silent to loud with different descriptions to describe the sound. The odor may also vary, from flatus that has almost no odor, to an unpleasantly aromatic or severely offensive smelling expulsion. A person may even report variations in temperature when passing flatus. However none of these factors are clinically significant.

Natural Bowel Gas Production in Humans

Flatus is a combination of several gases including methane, hydrogen and carbon dioxide with smaller quantities of hydrogen sulfide and nitrogen. The composition is a result of a number of processes that contribute to the presence of gas in the lower gut.

  1. Air swallowing (aerophagia) occurs in every person to varying degrees and excessive air swallowing is commonly associated with eating or drinking too fast, a blocked nose, mouth breathing, cigarette smoking and gum chewing. Most of the air is passed out through the mouth as a belch but residual amounts pass further down into the gut.
  2. Foods that are high in indigestible material like fiber and with high quantities of sulfur compounds are more likely to contribute to gas formation in the bowel. Carbonated beverages are another contributing factor although much of this gas is passed out through belching.
  3. Chemical digestion is the break down of foods by the action of digestive enzymes. These chemical reactions inadvertently lead to gas production (byproduct) in most instances.
  4. Intestinal bacteria contribute significantly to the presence of bowel gas. These naturally occurring microorganisms consume residual nutrients and waste products in the small and large intestine releasing gas as a byproduct.
  5. Blood gas diffusion contributes to a small amount of gas in the lumen of the gastrointestinal tract. Nitrogen diffuses out of the blood stream and into the gut while hydrogen may enter the blood stream from the gut.

Related Articles

  1. Excessive Flatulence
  2. Causes of Bloating and Gas (Flatulence)


  1. Gas-Related Complaints (Merck)

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