Gas is air in the intestine that is passed through the rectum. Air that moves from the digestive tract through the mouth is called belching.

Gas is also called flatus or flatulence.

Flatulence; Flatus

Gas is normally formed in the intestines as your body digests food.

Gas can make you feel bloated. It can cause crampy or colicky pains in your belly.

Gas can be caused by certain foods you eat. You may have gas if you:

• Eat foods that are hard to digest, such as fiber. Sometimes, adding more fiber into your diet can cause temporary gas. Your body may adjust and stop producing gas over time.
• Eat or drink something your body cannot tolerate. For example, some people have lactose intolerance and cannot eat or drink dairy products.

Other common causes of gas are:

• Antibiotics
• Irritable bowel syndrome
• Inability to absorb nutrients properly (malabsorption)
• Inability to digest nutrients properly (maldigestion)
• Swallowing air while eating
• Chewing gum
• Smoking cigarettes
• Drinking carbonated beverages
• Talking while eating and eating too rapidly

The following tips may help you prevent gas:

• Chew your food more thoroughly.
• Do not eat beans or cabbage.
• Avoid foods high in poorly digestible carbohydrates. These are called FODMAPs and include fructose (fruit sugar).
• Avoid lactose.
• Do not drink carbonated drinks.
• Do not chew gum.
• Eat more slowly.
• Relax while you eat.
• Walk for 10 to 15 minutes after eating.

Contact your health care provider if you have:

• Gas and other symptoms such as stomach pain, rectal pain, heartburn, nausea, vomiting, diarrhea, constipation, fever, or weight loss
• Oily, foul-smelling, or bloody stools

Your provider will perform a physical exam and ask questions about your medical history and symptoms, such as:

• What foods do you commonly eat?
• Has your diet changed recently?
• Have you increased the fiber in your diet?
• How fast do you eat, chew, and swallow?
• Would you say that your gas is mild or severe?
• Does your gas seem to be related to eating milk products or other specific foods?
• What seems to make your gas better?
• What medicines do you take?
• Do you have other symptoms, like abdominal pain, diarrhea, early satiety (premature fullness after meals), bloating, or weight loss?
• Do you chew artificially sweetened gum or eat artificially sweetened candy? (These frequently contain indigestible sugars that can lead to production of gas.)

Tests that may be done include:

• Abdominal CT scan
• Abdominal ultrasound
• Barium enema x-ray
• Barium swallow x-ray
• Blood work such as CBC or blood differential
• Sigmoidoscopy
• Upper endoscopy (EGD)
• Breath test

Azpiroz F. Intestinal gas. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 17.

Hall JE, Hall ME. Physiology of gastrointestinal disorders. In: Hall JE, Hall ME, eds. Guyton and Hall Textbook of Medical Physiology. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 67.

McQuaid KR. Approach to the patient with gastrointestinal disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 123.