Sources of Wind

There are three main sources of wind:

  • Everyone’s gut contains gas because we cannot help swallowing air when we swallow food, when we drink and when we swallow our saliva.
  • Carbon dioxide is produced by chemical reactions within the gut: saliva contains bicarbonate, which reacts with acid in the stomach to produce carbon dioxide gas; and stomach acid releases carbon dioxide when it reacts with pancreatic digestive juices in the upper part of the intestine.
  • About 500 types of bacteria live in our intestines. Some of them act on food residues in the lower gut, releasing hydrogen, methane and carbon dioxide gases.

What Happens to the Gas in the Gut?

Some of the intestinal gas is absorbed into the bloodstream and is eventually exhaled by the lungs. In social situations, we try to hold gas in and more passes from the gut into the bloodstream and then into the lungs; researchers have found that, in social situations, our breath contains increased amounts of hydrogen.

Most intestinal gas, however, has to be got rid of through the mouth (belching, eructation) or through the anus (flatulence, farting, breaking wind).

Why Wind Smells

The main gases in wind – nitrogen, oxygen, carbon dioxide, hydrogen and methane – have no smell. The unpleasant smell of a fart is due to very tiny amounts of sulphur-containing gases, which have a smell disproportionate to their volume.

Farting and Belching – Are They Healthy or Can They Spread Germs?

Some experts believe that our attempts to hold gas in are an unnatural result of our enclosed lifestyles and the build-up of pressure is responsible for bowel diseases, such as diverticulosis; when we lived mainly in the open air, farting was not a problem and no one was worried about letting wind pass out naturally. In the early 1990s, a publicity campaign was launched in Holland (by the National Liver and Intestine Foundation) to encourage people to break wind at least 15 times a day.

Wind is never serious, except as a cause of embarrassment, unless there are other gut symptoms as well, such as abdominal pain, constipation, loss of weight, pale poo that is difficult to flush away, or blood in the poo.

No one knows whether wind can spread germs. The magazine New Scientist (30 June 2001) reported an experiment in which a volunteer was asked to lower his trousers and break wind very close to a special dish (blood agar plate) used by laboratories to grow bacteria. The next day, there were lots of gut bacteria growing on the plate. At the edge, there were some skin bacteria that must have been blown onto the plate by the wind.

Fascinating Facts

  • Methane is one of the most potent greenhouse gases in the atmosphere. Cow’s and sheep’s wind is responsible for almost a third of the methane in Europe that passes into the atmosphere. A single sheep typically produces 25 litres of methane a day, while a cow can produce an amazing 280 litres a day (New Scientist 15 June 2002)
  • In the 1960s, NASA was worried that a build-up of hydrogen from astronauts’ wind might accidentally explode in the spacecraft. This stimulated a lot of research into bowel gas
  • At any one time, there is about 200 mL (a mugful) of gas in each person’s gut
  • Most people expel about 600 mL of gas/day, but some people produce up to 2 litres
  • Gut gases are 90% nitrogen; the remainder is carbon dioxide, hydrogen, methane and sometimes hydrogen sulphide
  • Healthy young men break wind 14–25 times a day and women half as often
  • Women produce stronger smelling flatus than men, but men produce a greater volume


First published on:
Reviewed and edited by: Dr Kevin Barrett
Last updated: October 2020

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