Gas (Flatulence)


What Is It?

Flatulence is the passage of intestinal gas (flatus) through the rectum. Passing gas is normal, and every human being does it at least 14 times a day, consciously or unconsciously. Sometimes, however, flatulence happens more often than expected, and this can become an embarrassing problem. Extreme flatulence can even interfere with a person’s ability to work and socialize comfortably with other people.

Most cases of flatulence are related to factors that can be controlled. This is because intestinal gas usually comes from two sources — swallowed air or the work of intestinal bacteria on undigested food.

Swallowing air is one cause of flatulence. Although much of this swallowed air is belched upwards through the mouth, a small amount passes into the intestines and out through the rectum. People swallow air in many different ways, particularly by:

  • Unconsciously gulping air as they talk, especially when they are upset, excited or nervous
  • Eating or drinking in a hurry
  • Chewing gum
  • Smoking
  • Drinking carbonated beverages

Bacteria in the intestines also can produce gas when they process foods that pass into the colon without being digested. Some common examples of foods that tend to cause gas include:

  • Foods rich in fiber — These include fruits, beans, peas and oat bran.

  • Foods containing fructose — Fructose is a simple sugar that occurs naturally in many fruits, especially figs, dates, prunes, pears and grapes. It’s also found in smaller amounts in onions, asparagus, artichokes and wheat. Fructose sometimes is added as a sweetener to soft drinks, fruit drinks and some cookies and cakes.

  • Vegetables containing raffinose — Raffinose is a complex sugar found in many cruciferous vegetables (cabbage, Brussels sprouts, broccoli, cauliflower) and in beans. Beans also contain stachyose, another form of poorly digested sugar.

  • Sorbitol — Sorbitol is used to sweeten many sugar-free gums and candies, and it also may be added as an inert ingredient to medicines.

  • Dairy products containing lactose, a sugar found in milk — People who are lactose intolerant find it difficult to digest milk, cheese, ice cream and other dairy products. These people have inherited unusually low levels of lactase, an enzyme needed to digest lactose. Lactose intolerance is especially common among African-Americans, Native Americans and Asians.

Less commonly, flatulence can be a side effect of certain medications, especially cholestyramine (Questran), used to treat High cholesterol, or the diet drug orlistat (Xenical). It also can be a symptom of irritable bowel syndrome or giardiasis (a parasitic infection).


Flatulence is the passing of intestinal gas, either voluntarily or involuntarily. Some people who have flatulence also complain of abdominal bloating, but others do not.


Usually a person with flatulence is aware of passing gas. Sometimes, it is more troublesome to other family members or co-workers.

To investigate the cause, examine your lifestyle, especially the way you eat your meals:

  • Do you often gulp your food on the run, or is your dinner table frequently the site of stressful family arguments?

  • Do you drink many carbonated beverages, or eat a lot of high-fiber fruits and vegetables, dairy products and sugar-free or diet foods? Keep a diary to record what you eat and drink, and the severity of your symptoms.

  • Are any prescription and nonprescription medications you take, including any diet drinks or diet meals, causing your flatulence? If you suspect that your problem is medication related, don’t stop taking it. Call your doctor for advice.

  • Are you lactose intolerant? Consider stopping all milk-based products for two weeks.

Expected Duration

How long flatulence lasts depends on its cause. If flatulence is related to eating habits or dietary factors, it often goes away quickly once you identify the source of the problem and make the necessary changes in diet or lifestyle.


You often can prevent flatulence by modifying your eating habits and diet:

  • Eat and drink slowly, in a calm environment. Chew your food thoroughly before you swallow.

  • For a few days, avoid the foods that most commonly cause flatulence, such as beans, high-fiber foods, cruciferous vegetables, carbonated beverages and sugar-free products containing sorbitol. Then gradually add them to your diet again, one by one, while keeping track of your symptoms. This should let you determine which foods trigger flatulence for you. Then you can avoid them.

  • If you need to add more fiber to your diet, increase your fiber slowly over a period of days or weeks. A sudden increase in dietary fiber often triggers flatulence, but a gradual increase may not.

  • If you eat beans, try a nonprescription product, such as Beano, containing enzymes that break up the poorly digested sugars found in beans.


You may reduce flatulence by trying:

  • Preventive steps
  • Nonprescription antigas medications containing simethicone (Mylanta II, Maalox II, Di-Gel) or bismuth (Pepto-Bismol, Bismatrol)
  • For lactose intolerance:

    • Take over-the-counter tablets or liquids containing the enzyme lactase before you eat or drink products containing milk.
    • Lactose-reduced dairy products are available in grocery stores.

When To Call A Professional

Call your doctor if you have flatulence that occurs along with abdominal discomfort, significant bloating or a sudden change in your bowel habits, either constipation or diarrhea. Also, call for advice if your attempts to reduce your flatulence have not worked.


Flatulence often can be controlled with a few minor changes in diet or lifestyle.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.