Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Font Size

The Digestive System and Gas

What Is Gas?

Gas is a normal byproduct of the foods we eat. As the digestive system breaks food down, it produces gas, which is mainly composed of carbon dioxide, oxygen, nitrogen, hydrogen, and methane.

Usually, we eliminate gas through the mouth (burping) or through the anus (flatulence). We typically pass gas around 20 times a day. Gas is an ordinary occurrence, but its presence can be painful and socially embarrassing.

Recommended Related to Digestive Disorders

Blood in Urine (Hematuria)

Blood in urine - known medically as hematuria - is usually not a reason for major alarm. Because blood in urine can be a sign of a serious medical condition, however, it shouldn't be ignored. All cases of hematuria should be evaluated by a doctor who can order tests to confirm or rule out an underlying cause. There is no specific treatment for hematuria, because it's a symptom and not a specific condition. Instead, treatment is aimed at the underlying cause if one can be found. In many cases,...

Read the Blood in Urine (Hematuria) article > >

What Causes Gas?

We produce gas in two ways: when we swallow air, and when the bacteria in the large intestine go to work helping to digest the food we eat.

Carbohydrates are especially troublesome. Humans cannot digest certain carbohydrates in the small intestine because we may not have (or not have enough of) the enzymes that can aid in their digestion. This food moves in the undigested state from the small intestine to the large intestine; it is here that the bacteria go to work, producing the gases hydrogen, carbon dioxide, and methane, which are then expelled from the body.

Not everybody will suffer from gas from eating the same foods.

We also swallow a certain amount of air when we eat and drink. This contributes to the production of gas. We usually release swallowed air by burping it out. Whatever isn't released by burping goes into the small or large intestine, where it is eventually released as flatulence.

Which Foods Are Most Likely to Produce Gas?

You are most likely to experience gas by eating carbohydrates, which are found in such foods as beans, vegetables (especially broccoli, cabbage, and onions), fruits, dairy products, whole grain foods, soft drinks, and fruit drinks.

What Are the Symptoms of Gas?

In addition to burping and flatulence, people who have gas may feel bloated. They may also have pain in the abdomen, which they may mistake for another disease, such as a heart attack or appendicitis.

Could Gas Be a Sign of a Medical Problem?

Yes. Chronic (long-lasting) belching may be a sign of disease in the upper digestive tract, such as ulcers or gastroesophageal reflux disease (GERD).

Bloating may be caused by a variety of diseases, including irritable bowel syndrome (IBS), colon cancer, Crohn's disease, or a hernia.

1 | 2 | 3

Today on WebMD

man holding his stomach
Get the facts on common problems.
blueberries in a palm
Best and worst foods.
woman shopping
Learn what foods to avoid.
fresh and dried plums
Will it help constipation?
top foods for probiotics
couple eating at cafe
sick child
Woman blowing bubble gum

Send yourself a link to download the app.

Loading ...

Please wait...

This feature is temporarily unavailable. Please try again later.


Now check your email account on your mobile phone to download your new app.

Woman with crohns in pain
Woman with stomach pain
diet for diverticulitis
what causes diarrhea