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Jonathan Gotfried

, MD, Lewis Katz School of Medicine at Temple University

Last full review/revision Mar 2020| Content last modified Mar 2020

Gas is normally present in the digestive system and may be expelled through the mouth (belching) or through the anus (flatus).

There are three main gas-related complaints:

  • Excessive belching (eructation)
  • Abdominal bloating (distention)
  • Excessive flatus (known colloquially as farting)

Belching is more likely to occur shortly after eating or during periods of stress. Some people feel a tightness in their chest or stomach just before belching that is relieved as the gas is expelled.

People who complain of flatulence often have a misconception of how much flatus people normally produce. There is great variability in the quantity and frequency of flatus. People typically have flatus about 13 to 21 times a day, amounting to ½ to 1½ quarts (0.5 to 1.5 liters), and some people pass flatus more or less often. Such gas may or may not have an odor.

Although flatus is flammable (due to the hydrogen and methane gas that it contains), this does not pose a routine problem. For example, working near open flames is not hazardous. However, there are rare reports of gas explosion during intestinal surgery and colonoscopy when electrical cautery was used in people whose bowels were incompletely cleaned out before the procedure.

In the past, colic in infants 2 to 4 months of age was attributed to excessive abdominal gas. Today, however, most doctors do not think colic is related to gas, because tests do not show excess gas in the abdomen of these infants. The actual cause of colic remains unclear.

Causes of Gas

Causes of gas vary depending on the gas-related symptom.


Belching is caused by

  • Swallowed air
  • Gas generated by carbonated beverages

People normally swallow small amounts of air while eating and drinking. However, some people unconsciously swallow larger amounts of air (aerophagia) repeatedly while eating or smoking and sometimes when they feel anxious or nervous. Excessive salivation, which may occur with gastroesophageal reflux, ill-fitting dentures, certain drugs, gum chewing, or nausea of any cause, also increases air swallowing.

Most swallowed air is later belched up, and very little passes from the stomach into the rest of the digestive system. The small amount of air that does pass into the intestines is mostly absorbed into the bloodstream and very little is passed as flatus.


Flatus results from hydrogen, methane, and carbon dioxide gases that are produced by the bacteria normally present in the large intestine. These bacteria always produce some gas, but excessive gas can be produced

  • When people consume certain foods
  • When the digestive tract is unable to absorb food properly (malabsorption syndromes)

Foods that increase gas production include any with poorly digestible carbohydrates (for example, dietary fiber such as in baked beans and cabbage), certain sugars (such as fructose), lactose-containing foods (such as milk), or sugar alcohols (such as sorbitol), and fats. Almost anyone who eats large amounts of vegetables or fruits develops some degree of flatulence.

Malabsorption syndromes can increase gas production. People who have carbohydrate deficiencies (deficiencies of the enzymes that break down certain sugars), such as those with lactase deficiency, tend to produce large amounts of gas when they eat foods containing these sugars. Other malabsorption syndromes, such as tropical sprue, celiac disease, and pancreatic insufficiency, also may lead to the production of large amounts of gas.

However, some people may simply have more or different bacteria naturally living in their digestive tract, or they may have a motility (movement) disorder of the muscles in their digestive tract. These variations may account for differences in flatus production. People can record their flatus frequency in a diary before being evaluated by a doctor.


A sensation of bloating or abdominal swelling (distention) can be present in people who have digestive disorders such as poor stomach emptying (gastroparesis) or irritable bowel syndrome or other physical disorders such as ovarian cancer or colon cancer. Many drugs with anticholinergic affects can slow stomach emptying and cause bloating. Sometimes, the sensation is caused by disorders that do not involve the abdomen. For example, in some people, the only symptom of a heart attack is a feeling of bloating or a strong urge to belch. However, many people who feel bloated do not have any physical disorder.

Doctors are not sure what role intestinal gas plays in the sensation of bloating. Aside from people who drink carbonated beverages or swallow excessive air, most people who have a sensation of bloating actually do not have excessive gas in their digestive system. However, studies do show that some people, such as those who have irritable bowel syndrome, are particularly sensitive to normal amounts of gas. Similarly, people with eating disorders (such as anorexia nervosa or bulimia) often misperceive and are particularly stressed by symptoms such as bloating. Thus, the basic abnormality in people with gas-related symptoms may be an intestine that is extremely sensitive (hypersensitive intestine). A motility disorder may contribute to symptoms as well.

Evaluation of Gas

Most gas-related symptoms do not require immediate evaluation by a doctor. The following information can help people decide whether a doctor’s evaluation is needed and help them know what to expect during the evaluation.

Warning signs

In people with gas, certain symptoms and characteristics are cause for concern. They include

  • Weight loss (unintentional)
  • Blood in stool
  • Chest pain

When to see a doctor

People with a bloating sensation in their chest, especially if the bloating sensation is accompanied by chest pain, should see a doctor promptly because this may be a sign of heart disease. People with any gas-related symptoms who have other warning signs, abdominal discomfort, or diarrhea should see a doctor within a week or so. People who have none of these symptoms or signs should see a doctor at some point, but it is not urgent.

What the doctor does

Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the symptoms and the tests that may need to be done (see Table: Some Causes and Features of Gas-Related Complaints).

For excessive belching, the history is focused on finding the cause of air swallowing, especially dietary causes. For excessive flatus, doctors seek dietary causes and also symptoms of malabsorption (such as diarrhea and/or fatty, foul-smelling stool).

In people with any gas-related complaint, doctors need to understand the relationship between symptoms and meals (both timing and type and amount of food) and bowel movements. Doctors ask people about changes in frequency and color and consistency of stool. Doctors also need to know whether people have lost any weight.

In people with bloating or flatus, the physical examination is focused on finding signs of an underlying physical disorder (such as ovarian cancer). Doctors do abdominal, rectal, and (for women) pelvic examinations.

Some Causes and Features of Gas-Related Complaints


Common Features*



Air swallowing

People with or without awareness of swallowing air

Sometimes in people who smoke or chew gum excessively

Sometimes in people who have esophageal reflux or ill-fitting dentures

A doctor’s examination

Gas from carbonated beverages

Beverage consumption usually obvious based on person’s history

A doctor’s examination

Distention or bloating

Air swallowing

See Belching, above

A doctor’s examination

Irritable bowel syndrome

Abdominal pain related to defecation, associated with a change in the frequency or consistency of stool, or both

No warning signs

Typically begins during adolescence and the 20s

A doctor’s examination

Examination of stool

Blood tests

Poor emptying of the stomach (gastroparesis), usually due to other disorders such as diabetes, connective tissue disorders, or neurologic disorders

Nausea, abdominal pain, and sometimes vomiting

Early fullness (satiety)

Sometimes in people known to have a disorder that causes it

Sometimes in people taking drugs with anticholinergic effects

Upper endoscopy‡ and/or nuclear scanning that evaluates stomach emptying

If a drug cause is suspected, stopping the drug to see whether symptoms go away

Eating disorders

Long-standing symptoms, particularly in young women

In people who are thin but still very concerned about excess body weight

A doctor’s examination

Chronic constipation

A long history of hard, infrequent bowel movements

A doctor’s examination

Cancer (rarely) of the ovary or large intestine

New, persistent bloating in middle-aged or older people

For colon cancer, sometimes blood in stool (blood may be visible or detected during a doctor's examination)

If ovarian cancer is suspected, ultrasonography of the pelvis

If colon cancer is suspected, colonoscopy

Passing of gas (flatulence)

Foods, including beans, dairy products, vegetables (such as onions, celery, carrots, or Brussels sprouts), fruits (such as raisins, bananas, apricots, and dates or apple, pear, or prune juice), and foods containing fructose (such as cola sodas, honey, or nuts), prunes, or waffle or maple syrup, or complex carbohydrates (such as pretzels, bagels, or wheat germ)

Symptoms that develop mainly when food that can cause gas is consumed

A doctor’s examination

Elimination of the suspected food from diet to see whether symptoms go away

Lactose intolerance

Bloating, cramps, and diarrhea after consuming milk products

A breath test to detect hydrogen, indicating undigested food

Celiac disease

Light-colored, soft, bulky, and unusually foul-smelling stools that may appear oily

Weakness, loss of appetite, and diarrhea

Often begins in childhood

Blood tests to measure antibodies produced when people with celiac disease eat foods containing gluten and biopsy of the upper small intestine

Tropical sprue

Light-colored, soft, bulky, and unusually foul-smelling stools that may appear oily

Nausea, loss of appetite, diarrhea, abdominal cramps, and weight loss

Blood tests and biopsy of the small intestine

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present.

† Doctors usually do a urine pregnancy test for all girls and women of childbearing age.

‡ Upper endoscopy is examination of the esophagus, stomach, and the first segment of the small intestine (duodenum) using a flexible viewing tube called an endoscope.


Doctors do not usually do any testing on people with gas-related complaints unless they have other symptoms that suggest a specific disorder (see Table: Some Causes and Features of Gas-Related Complaints). For example, people who also have diarrhea may need testing for a malabsorption syndrome.

An exception is middle age or older people who develop persistent bloating or distention, particularly those who have not had digestive system symptoms in the past. For such people, doctors may do tests for cancer of the ovary and/or colon.

Treatment of Gas

Doctors reassure people who have chronic bloating or flatus that their condition is not caused by another disorder and that these gas-related symptoms are not harmful to their health.

Bloating and belching are difficult to relieve because they are usually caused by unconscious air swallowing or an increased sensitivity to normal amounts of gas. If belching is the main problem, reducing the amount of air being swallowed can help, which is difficult because people usually are not aware of swallowing air. Avoiding chewing gum and eating more slowly in a relaxed atmosphere may help. Avoiding carbonated beverages helps some people. Doctors may also recommend that people try to minimize air swallowing by practicing open-mouth breathing from the diaphragm and fully control any associated upper digestive tract diseases (such as peptic ulcers).

People who pass flatus excessively should avoid foods that are likely to cause flatus. Typically, people should eliminate one food or group of foods at a time. Thus, people can start by eliminating foods containing hard-to-digest carbohydrates (such as beans and cabbage), then milk and dairy products, then fresh fruits, and then certain vegetables and other foods. Roughage (such as bran and psyllium seeds) may be added to the diet to try to increase movement through the large intestine. However, additional roughage may make symptoms worse for some people.

Drug treatment

Drugs do not provide much relief. Some doctors try anticholinergic drugs (such as bethanechol) and simethicone, which is present in some antacids and is also available by itself. However, there is little scientific evidence that these are of benefit.

Activated charcoal tablets can sometimes help reduce flatus and its unpleasant odor. However, charcoal stains the mouth and clothing. Charcoal-lined undergarments are available.

Probiotics, which are bacteria found naturally in the body that promote the growth of good bacteria, may reduce bloating and flatulence by promoting growth of normal intestinal bacteria in some people.

Some people with indigestion (dyspepsia) and upper abdominal fullness after a meal may be helped by antacids, a low dose of antidepressants (such as nortriptyline), or both to reduce a hypersensitive intestine.

Key Points about Gas

  • Testing is done mainly when other symptoms suggest a certain disorder.
  • Doctors should be aware of new and persistent symptoms of bloating in older people.

Drugs Mentioned In This Article

Generic Name Select Brand Names
nortriptyline AVENTYL
simethicone No US brand name

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