What happens when you hold in a fart?

Imagine being on a first date when you feel the need to toot your own horn — that is, pass gas. The average person releases about 0.5 to 1.5 liters (0.1 to 0.4 gallons) of gas a day. Most of these farts are odorless, but it's rarely acceptable to take the chance and break wind. Whether in the workplace or with friends, we all clench our cheeks from time to time.

But what does holding in flatulence do to our bodies? Gas is a natural byproduct of digestion, and holding it in can cause discomfort, bloating and even nausea. But according to Dr. Ellen Stein, a gastroenterologist at RWJ Barnabas Health in New Jersey and a spokesperson for the American Gastroenterological Association, the body has other ways of handling this gas buildup.

"There's lots of different changes and cycles that happen with the bacteria that's in our gut that helps us to digest," Stein told Live Science. "The good news is that we have a process for it; the bad news is that gas has to pass eventually."

From the moment you take a bite of food, your body begins breaking it down mechanically and chemically. For instance, your teeth mechanically mash the food, and your saliva breaks it down chemically. As food Travels down the digestive tract, it's broken down further in the stomach, small intestine and large intestine. Microbes in the gut help break down the food into its most basic building blocks. Then, these building blocks can be absorbed into the bloodstream and delivered throughout the body as energy.

But not everything in food can be used by the body, especially if the body can't fully break down certain substances. For example, people with lactose intolerance don't make enough of the enzyme lactase in their small intestine, so lactose, a sugar in dairy products, stays and ferments in the digestive system, causing symptoms such as bloating, diarrhea and excessive gas.

However, gas builds up even in typical digestion. According to the American Society for Microbiology, hydrogen sulfide (which can cause the rotten-egg smell in farts) is made by friendly bacteria in the gut that breaks down proteins. Farther down the digestive tract, carbohydrates are broken down in the large intestine, and their byproducts of hydrogen and methane are added to the gas building up in the body. Even oxygen and carbon dioxide can be present in the gut, taken in when a person swallows food, Stein said.

Related: Which foods make the smelliest farts?