Why do farts stink?

Over the course of a day, most of us fart between 10 and 20 times, typically during the night.

Sometimes they emerge as a loud fart, and other times as a stealthy one.

However, despite the fact that a fart can fill a room with a stench, the majority of the gas is completely odourless.

Researchers have actually measured the content of farts in many people. They found that 99 per cent of the gas is odourless.

Smells like rotten eggs

So, what is the one per cent that smells so bad?

These gases all contain sulphur. The worst offendor is hydrogen sulphide. This gas smells like rotten eggs.

“Hydrogen sulphide is a stink bomb,” says Trygve Hausken.

He is a retired doctor and researcher, and an expert on intestines.

A bit of gas leads to a lot of odour

Foods containing sulphur such as onions, cauliflower, cabbage, red meat, and eggs are particularly appetising to a certain type of bacteria in the intestine.

These bacteria feast on the remnants of the food. They break it down and release foul-smelling gases.

Even tiny amounts of sulphur gas in a fart are noticeably pungent.

“A little goes a long way in terms of smell,” Hausken says.

Bloated like a balloon

The rest of the gas produced by bacteria smells like nothing.

Our intestinal microbes mainly produce large amounts of carbon dioxide and hydrogen. Some of us also host bacteria that generate methane, much like cows.

This type of gas does not smell either.

However, excessive intestinal gas can cause discomfort beyond just bad odours.

It can lead to stomach pain and a feeling of being bloated like a balloon.

Difficult to digest beans and cabbage

Which foods cause the most gas? Foods are generally categorised into fats, proteins, and carbohydrates.

Carbohydrates are the main culprits for gas production in the gut, explains Hausken.

Some carbs, like sugars and starches, are easily digested. Others are indigestible by our bodies and thus become a feast for our intestinal bacteria.

“When the gut bacteria find something they like, they produce a lot of gas,” says Hausken.

This is especially true for foods such as beans, broccoli, cabbage, and whole grains.

Farting out swallowed air

However, bacteria are not the only source of flatulence.

When researchers have examined what a fart contains, they often find a lot of nitrogen gas. There may also be some oxygen.

These gases are simply from swallowed air. Throughout the day, we ingest significant amounts of air.

This air must exit the body, either as a burp or a fart.

As the swallowed air moves through the intestines, it mixes with bacterial gases.

Let it out

Large gas pockets in the intestines can cause quite a loud disturbance when released.

If there are large pockets of gas in the intestines, it can quickly become noisy when you let it out.

But it's important not to hold in farts, Hausken advises.

“Let it out, get it out, that’s the best advice,” he says.

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Translated by Alette Bjordal Gjellesvik

Read the Norwegian version of this article on ung.forskning.no

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