According to the dictionary, to belch is "to bring forth wind noisily from the stomach." The interchangeable word "burp" does not appear in some dictionaries, but it seems to mean, "cause to belch."

Belching after a large meal is a normal, necessary venting of air from the stomach. In some societies it is a gesture of appreciation to the host. 

Nevertheless, for some people, belching is a serious and difficult matter. They are plagued by sudden attacks of belching which is both intrusive and embarrassing. It may cause concern that the gas or air that is belched originates in the "stomach," and that it is an indication of an underlying gas-producing disease.

Fortunately, that is rarely the case, and a doctor’s assessment should be reassuring. Indeed, all available evidence points to swallowed air as the source of the stomach gas and the perceived need to bring it up. This process is called aerophagia.

Aerophagia

Air swallowing is normal, although it contributes no discernible benefit. Newborns have no gas in their intestines until they draw their first breath. Subsequently air appears progressively down the gut. Normally, the esophagus contains some swallowed air. In a disorder called achalasia, where the valve at the lower end of the esophagus cannot relax, the stomach contains no gas at all.

Learn more about achalasia

During inhalation, the pressure in the esophagus falls, drawing in air. Deliberate inhalation against a willfully closed windpipe draws even more air into the esophagus.

Commonly, aerophagia is an unwanted habit in those who repeatedly burp, sometimes in response to a sense of abdominal bloating (but belching and abdominal bloating often occur independently).

When a person swallows saliva, about 5 mL of air is ingested, and more is ingested during a meal. We accumulate more intestinal gas when nervous than when relaxed. Other mechanisms include thumb sucking, gum chewing, rapid eating, and poor dentures.

Stomach gas has the same composition as the atmosphere and the volume increases about 10% when heated by body temperature. Carbonated drinks and antacids reacting with hydrochloric acid produce carbon dioxide and traces may diffuse from the blood. However, the stomach usually rids itself promptly of gas. For example, air forced into the stomach during a stomach examination (endoscopy) often appears in the rectum within 15 minutes.

Almost all stomach gas is ingested in this way. Exceptions include bowel obstruction or a fistula (opening from the colon to the stomach as a result of disease). This directs colon gases into the stomach. Occasionally, paralysis of the stomach permits bacteria to grow and produce hydrogen.

When the stomach is distended by a meal, the stretched muscle results in feeling of fullness (satiety) or sometimes discomfort. A satisfying belch may ease this feeling.

The ability to tolerate stomach distension varies, and some individuals seem unduly sensitive. If release of gas relieves the distended feeling, even transiently, a cycle of air swallowing and belching may be established.

People with gastroenteritis, heartburn, or ulcers swallow more frequently, but the ensuing belch is probably a counter stimulus of no lasting benefit. The swallow-belch cycle may continue long after the original discomfort is forgotten.

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