An underlying chronic digestive disorder such as inflammatory bowel disease or diverticulitis causes excess gas formation. Inflammation of or obstruction in the colon in people suffering from these chronic conditions inhibits normal contraction of the colon. When the colon fails to contract properly, the intestinal gas cannot move out of the colon. As a result, gas accumulates in the colon, resulting in pain and discomfort. In addition, changes in the intestines impair digestion, increasing the amount of undigested food in the intestines, thereby leading to excess gas formation.

Constipation obstructs the gas from moving out of the rectum, resulting in gas build up in the stomach and intestines.

Excess gas is a common side effect of prolonged use of certain laxatives. Certain oral laxatives might prevent absorption of some food nutrients, increasing the load of undigested food in the large intestine. Bulk forming laxative, although safe for long term use, can cause gas if not taken with sufficient water.

The normal microbial balance in the gut plays an important role in inhibiting excess gas formation during digestion. Gas produced by some bacteria during digestion is often absorbed by other bacteria in the gut, reducing the overall gas output. Antibiotics can disrupt the normal microbial flora in the large intestine, thereby increasing gas formation.

Many people develop gas after consuming artificial additives or sweeteners. It is more likely to occur after consuming candies, gums or other sugar-free foods with mannitol or sorbitol.

Food intolerance can result in excess gas formation. It usually occurs in people intolerant to dairy products or gluten. Gluten intolerance, also known as celiac disease, might increase gas formation along with abdominal discomfort, bloating and diarrhea following consumption of grains such as wheat, barley, rye and other grains that contain a protein known as gliadin. Lactose intolerance occurs when the small intestine lacks the enzyme lactase that aids digestion of milk and dairy products.

Carbohydrates can also contribute to gas formation. Owing to absence or deficiency of certain enzymes, certain sugars, such as fructose, lactose, raffinose and sorbitol, are not completely digested in the small intestine. The undigested sugars move into the colon, where they are broken down by the bacteria. Fructose occurs naturally in pears, onions, artichokes, wheat and several fruits. Milk and dairy contains lactose. Raffinose is found in large quantities in beans and in smaller amounts in cabbage, broccoli, asparagus and Brussels sprout. Sorbitol is present in fruits. Starchy vegetables and grains other than rice produce gas when they are digested in the large intestine.

Consuming fiber rich foods is a common cause of gas in the stomach. A large number of fruits and vegetables are packed with soluble and insoluble fibers. Legumes, whole grains and most fruits and vegetables are rich sources of soluble fibers. Soluble fibers are largely responsible for gas formation. They are digested in the large intestine, where harmless bacteria break them into digestible substances, producing gases such as carbon dioxide, hydrogen, and small amount of methane and hydrogen sulfide in the process. Adding fiber supplement to the diet can also cause gas, especially when a person accustomed to a low fiber diet rapidly increases fiber intake. However, insoluble fibers, that pass almost unchanged throughout the digestive tract, rarely induce gas production.

Swallowing excess air, while eating or drinking, leads to gas build up in the stomach. It is normal to swallow a small amount of air every time we eat or drink. However, excess air swallowing or aerophagia occurs while eating rapidly, sucking candies, chewing gum and drinking through a straw. People who wear loose dentures have a higher risk of swallowing excess air. The larger part of the swallowed air escapes from the stomach through belching or burping. The remaining gas, if not absorbed in the small intestine, is expelled through the rectum.