Why Do People Fart?

A few years ago, I was doing a routine checkup on a delightful 5-year-old girl. One of the things I do at checkups is to ask kids to bend over so I can see if they have a straight back. I do this while I’m sitting on a stool behind the child. As soon as the girl bent over to touch her toes, she let out a big fart that blasted me right in the face! Her mom was embarrassed, but the girl and I both started to laugh. (Passing gas is no big deal to me since I spend every day with babies and little kids who fill their diapers with lots of smelly stuff.)

Of course, the real question is why it happens in the first place? Last month, I wrote an article on burps. I wrote that burps were caused by swallowed air that rose to the top of your stomach and came out as a belch. I also mentioned that not all of the air a person swallows comes back up. Therefore, most farts are simply the result of swallowed air that made the long journey from your mouth to your anus.

But that is not the whole picture. We all know that bacteria can make us sick. If you’ve ever had a strep throat or an ear infection, some nasty bacteria was responsible for the illness. That said, most bacteria in the world are not only benign (that means they’re harmless), but lots of them actually help us.

Your large intestine is home to trillions of bacteria. These microscopic creatures rummage around in soupy material that is made up of water, chemicals and undigested food that was not absorbed from your small intestine. As this waste moves through your large intestine, two things happen. First, water is absorbed so you can pass a nice, firm poop. Second, the bacteria have a smorgasbord of food to gorge on. (When it comes to “eating” bacteria are not as discriminating as people.)

As your intestinal bacteria digest the “leftovers” in your fecal material, they produce gases that add to the swallowed air already in your body. Farts are made up of oxygen, nitrogen, hydrogen, carbon dioxide, methane and hydrogen sulfide. Most are odorless. The reason some farts smell is due to the presence of small amounts of hydrogen sulfide. This is what gives farts a rotten egg smell and the bad reputation they deserve.

Although the average person farts 14 times per day, most people keep their farts to themselves. However, kids (of all ages) love to share farts with their friends and family.

Bonus Fact: Everyone knows that there are many types of farts—squeakers, boomers, foghorns, tooters, wet-ones and SBDs. However, do you know the name of the loud, rumbling noise that’s made when gas and liquids move through your intestines? The word for this “pre-fart” is called borborygmus (bor-bor-ig-muss). If you ever study poetry, you will learn that this word is the perfect example of onomatopoeia, that is, it sounds like what it means.

First Published in the Washington Post, February 8, 2010

Dr. Howard Bennett

About Dr. Bennett

Dr. Howard Bennett is a pediatrician in Washington, D.C. When he's not taking care of kids, Dr. Bennett writes about gross things for Jack and Jill and the KidsPost section of The Washington Post. He has also written six books for children. Check out Dr. Bennett's website, www.howardjbennett.com, for his KidsPost articles, a Lego slide show, and lots of other cool stuff.

Books by Dr. Bennett

In addition to his columns, Dr. Howard has written the following books for kids and parents:

"It Hurts When I Poop!"

A Story for Children Who Are Scared to Use the Potty

"The Case of
the Wet Bed

A Max Archer Kid Detective book.

"Waking Up Dry"

A Guide to Help Children Overcome Bedwetting

"Lions Aren't
Scared of Shots

A Story About Visiting the Doctor

"Harry Goes to the Hospital"

A Story for Children About What It’s Like to Be In the Hospital