What is gas and What causes gas ?

What is gas?

Gas is air in the digestive tract—the large, muscular tube that extends from the mouth to the anus, where the movement of muscles, along with the release of hormones and enzymes, allows for the digestion of food. Gas leaves the body when people burp through the mouth or pass gas through the anus.

Gas is primarily composed of carbon dioxide, oxygen, nitrogen, hydrogen, and sometimes methane. Flatus, gas passed through the anus, may also contain small amounts of gasses that contain sulfur. Flatus that contains more sulfur gasses has more odor.

Everyone has gas. However, many people think they burp or pass gas too often and that they have too much gas. Having too much gas is rare.

What causes gas?

Gas in the digestive tract is usually caused by swallowing air and by the breakdown of certain foods in the large intestine by bacteria.

Everyone swallows a small amount of air when eating and drinking. The amount of air swallowed increases when people

    eat or drink too fast

    smoke

    chew gum

    suck on hard candy

    drink carbonated or “fizzy” drinks

    wear loose-fitting dentures

Drawing of the digestive tract inside the outline of a man’s torso with labels pointing to the mouth, esophagus, stomach, small intestine, large intestine, colon, rectum, and anus.

The digestive tract

Burping allows some gas to leave the stomach. The remaining gas moves into the small intestine, where it is partially absorbed. A small amount travels into the large intestine for release through the anus.

The stomach and small intestine do not fully digest some carbohydrates—sugars, starches, and fiber found in many foods. This undigested food passes through the small intestine to the large intestine. Once there, undigested carbohydrates are broken down by bacteria in the large intestine, which release hydrogen and carbon dioxide in the process. Other types of bacteria in the large intestine take in hydrogen gas and create methane gas or hydrogen sulfide, the most common sulfur gas in flatus.

Studies have detected methane in the breath of 30 to 62 percent of healthy adults.1 A larger percentage of adults may produce methane in the intestines, but the levels may be too low to be detected. Research suggests that people with conditions that cause constipation are more likely to produce detectable amounts of methane.1 More research is needed to find out the reasons for differences in methane production and to explore the relationship between methane and other health problems.

Some of the gas produced in the intestines is absorbed by the bloodstream and carried to the lungs, where it is released in the breath.