Intestinal Gas (Belching, Bloating, Flatulence)

  • Medical Author:
    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What causes belching or burping?

The ability to belch is almost universal. Belching, also known as burping (medically referred to as eructation), is the act of expelling gas from the stomach out through the mouth. The usual cause of belching is a distended (inflated) stomach caused by swallowed air. The distention of the stomach causes abdominal discomfort, and the belching expels the air and relieves the discomfort. The common reasons for swallowing large amounts of air (aerophagia) are gulping food or drink too rapidly, anxiety, and carbonated beverages. People are often unaware that they are swallowing air. "Burping" infants during bottle or breastfeeding is important in order to expel air in the stomach that has been swallowed with the formula or milk.

Excessive air in the stomach is not the only cause of belching. For some people, belching becomes a habit and does not reflect the amount of air in their stomachs. For others, belching is a response to any type of abdominal discomfort and not just to discomfort due to increased gas. Everyone knows that when they have mild abdominal discomfort, belching often relieves the problem. This is because excessive air in the stomach often is the cause of mild abdominal discomfort. As a result, people belch whenever mild abdominal discomfort is felt regardless of its cause.

Belching is not the simple act that many people think it is. Belching requires the coordination of several activities.

  • The larynx must be closed-off so that any liquid or food that might return with the air from the stomach won't get into the lungs.
  • This is accomplished by voluntarily raising the larynx as is done when swallowing.
  • Raising the larynx also relaxes the upper esophageal sphincter so that air can pass more easily from the esophagus into the throat.
  • The lower esophageal sphincter must open so that air can pass from the stomach into the esophagus.
  • While all this is occurring, the diaphragm descends just as it does when a breath is taken.
  • This increases abdominal pressure and decreases pressure in the chest.
  • The changes in pressure promote the flow of air from the stomach in the abdomen to the esophagus in the chest.

One unusual type of belching has been described in individuals who habitually belch. It has been demonstrated that during their belches, air in the room enters the esophagus and is immediately expelled without even entering the stomach, giving rise to a belch. This in and out flow of air also is likely to be the explanation for the ability of many people to belch at will, even when there is little or no air in the stomach. Such belching is referred to as esophageal belching.

If the problem causing the discomfort is not excessive air in the stomach, then belching does not provide relief from the discomfort. When belching does not ease the discomfort, the belching should be taken as a sign that something may be wrong within the abdomen, and the cause of the discomfort should be sought. Belching by itself, however, does not help the physician determine what may be wrong because belching can occur in virtually any abdominal disease or condition that causes abdominal discomfort.

What causes bloating?

It is important to distinguish between bloating and distention.

  • Bloating is the subjective sensation (feeling) that the abdomen is full or larger than normal. Thus, bloating is a symptom akin to the symptom of discomfort.
  • In contrast, distention is the objective determination (physical finding) that the abdomen is larger than normal. Distention can be determined by such observations as the inability to fit into clothes, the need to loosen the belt or looking down at the stomach and noting that it is clearly larger than normal.

In some instances, bloating may represent a mild form of distention since the abdomen does not become physically (visibly or measurably) enlarged until its volume increases by one quart. Bloating and even mild cases of distention may be caused by relaxation of the muscles of the abdominal wall and downward movement of the diaphragm.

There are three ways in which abdominal distention can arise. The causes are an increase in air, fluid, or tissue within the abdomen. The diseases or conditions that cause an increase of air, fluid, or tissue are very different from one another. Therefore, it is important to determine what (air, fluid, tissue) is distending the abdomen.

There are two types of distention; continuous and intermittent.

  • Continuous distention may be caused by the enlargement of an intra-abdominal (within the abdomen) organ, an intra-abdominal tumor, a collection of fluid within the peritoneal cavity, the space that surrounds the intra-abdominal organs (ascites), or just plain obesity.
  • Intermittent distention is usually due to the accumulation of gas and/or occasionally, fluid within the stomach, small intestine, or colon.
Medically Reviewed by a Doctor on 4/7/2017

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