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I have read in this link that farts can come out of your mouth. But I don't know how much I can trust the internet, and I am no expert in medicine or human health whatsoever.

Is this true? And if so, can someone explain it a bit better? How can the gas go all the way up to the mouth again?

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    The article is just dramatizing belches with the word fart. Calling fermentation gases from the small intestines a fart isn't really accurate. – Carey Gregory Jul 13 '18 at 0:05
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The linked article's title and subtitle are in contradiction with the article's content.

The title and subtitle say:

THIS IS WHAT HAPPENS TO YOUR BODY WHEN YOU HOLD IN A FART...If you keep one inside too long, it can bubble up to your mouth instead...

But the text says:

...gas literally bubbling up from your intestines and coming out as a burp...That’s because, at this point in the digestive process, the gas is still much closer to your mouth than your anus.

The gas discussed above is the gas in the first part of the small intestine (just after the stomach). When this gas comes out from the mouth it is called a burp and when it comes out from the anus, it's called a fart or flatulence. So, it's not even theoretically possible that a fart comes out of your mouth.

The subtitle of the article claims that holding a fart can result in gas coming out of your mouth. This is not likely. You can voluntary hold in a fart only at the level of the anus, and once gas reaches the anus it will not travel all the way back to the mouth. The same way, if you hold in the stool, it won't come out of your mouth. Gases and other bowel contents can probably flow backward only from the stomach and first part of the small intestine (the duodenum). For example, the bile from the duodenum can appear in the vomit.

If you hold a fart, some gas will be absorbed in the large intestine and some will be eventually released.

The gas that comes out of your mouth during burping (belching) can be swallowed air or it can originate from fermentation of nutrients by microbes in the stomach or small intestine. The gas that comes out of the anus (flatulence) originates from fermentation in the large intestine.

Frequent burping can occur due to:

  • Swallowing air during eating or smoking
  • Drinking carbonated beverages
  • Chewing gum or eating foods high in sugar alcohols, such as sorbitol or xylitol
  • Acid reflux
  • Irritable bowel syndrome
  • H. pylori infection of the stomach
  • Fructose malabsorption
  • Lactose intolerance
  • Small intestinal bacterial overgrowth (SIBO)
  • Infestation with intestinal parasites, such as Giardia
  • Impaired stomach emptying (gastroparesis), for example, as a complication of diabetes

Other references:

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  • And how does this fermentation differ from gas? – Narusan Jul 13 '18 at 12:31
  • Burping is caused by fermentation in the stomach and first part of the small intestine, while gas (flatulence) results from fermentation in the large intestine. The common nutrients involved in both cases are sugars, sugar alcohols and fiber. – Jan Jul 13 '18 at 16:52
  • I know, but maybe you should include that in the answer, as that clarifies that they aren't really the same as flatulence – Narusan Jul 13 '18 at 16:55
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    OK, I realized that the real question was if holding gas can result in the gas coming out of your mouth. – Jan Jul 14 '18 at 9:01

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