Why Silent Farts Are Smellier Than Loud Farts

Everybody toots, but some toots can clear the room.

Understanding why your body farts might help you understand more about your gut – and could help you understand signs of what is and what isn’t normal flatulence.

“It’s OK to be gassy because sometimes it suggests that you’re just eating a healthy diet,” said Dr. Kyle Staller, a gastroenterologist and the director of the Gastrointestinal Motility Laboratory at Massachusetts General Hospital. “We all do it. It’s just not something that people talk about socially.”

People can make the mistake of believing that a smelly fart means that what you ate was bad or stuck in your body forever, but that’s not necessarily true.

“Your colon is very efficient at moving gas along, and so it’s probably less likely that it was in there longer, and more likely reflective of what you ate and how your body was able to absorb or not absorb it,” Staller said.

When your fart sounds like a loud trumpet, it’s because what you ate produced a large volume of gas.

For example, when your body digests certain carbohydrates, it can produce large volumes of nitrogen, hydrogen and carbon dioxide gases that are mostly odorless. “The higher volume [of gases] creates more vibration, and that’s why you get these loud, large-volume farts,” Staller said.

Sometimes, how you eat your food can also be why your farts are loud. In these cases, it’s due to “mostly swallowed air that moves quickly through the digestive tract, causing vibrations in the anal sphincter that create the loud noise,” said Dr. Supriya Rao, a gastroenterologist.

But when your silent toot smells rotten, it’s usually because of the gases produced by what you just ate.

When you eat proteins that are full of sulfur-containing amino acids, they can produce a very smelly gas called hydrogen sulfide. Common examples include red meat, eggs, dairy, and cruciferous vegetables like broccoli, cauliflower or cabbage, Staller said. Eating these sulfur-containing amino acids can result in a small quantity of gas, so your fart might not make noise, but it’s very potent.

“You’re not making as much volume of gas because proteins in general don’t break down into a lot of gas, but that small volume of gas when it comes out is very enriched,” Staller said. “That small amount of smelly gas gets pushed out, and it comes out in a silent-but-deadly type of passage.”

To toot is to be human. Occasional smelly farts are an occupational hazard with eating proteins that contain sulfur, like meat or dairy. If you want these smelly farts to stop, “pay attention to what foods you eat and see if you can identify any triggers,” Rao said.

Rao said eating more slowly and drinking more water can sometimes alleviate smelly gases. But at the same time, unexpected, regular smelly flatulence can be telling you something deeper about your gut health.

“Passing gas is a normal part of life,” Staller said. “But if you are now suddenly passing gas that’s malodorous like you’ve never done before, and you haven’t clearly changed your diet in a meaningful way, I think that’s when it’s worth talking to a healthcare professional because the most common cause of this is lactose intolerance.”

Smelly farts can be a sign that your body might be having trouble absorbing nutrients. When people cannot absorb lactose, for example, they are lacking an enzyme in sufficient quantities to break it down, which can lead to smelly farts, Staller said.

Staller noted that smelly farts can also sometimes be a sign that you are dealing with celiac disease or a gluten intolerance caused by an autoimmune disease, which can develop at any point in life. And more recently, a smelly fart could also be a symptom of this summer’s exploding diarrhoea illness in the U.S. known as cyclosporiasis.

When people have cyclosporiasis, “the cells lining your small intestine are what absorb most of your nutrients from your food, and cyclosporiasis damages those cells,” Staller explained. Although, to be clear, “most people with cyclosporiasis are going to have more than just malodorous gas,” he added.

Of course, if you are farting and you also have abdominal pain, unexplained weight loss, blood in your stool or changes in bowel habits, you should also tell your doctor, Rao noted.

So, know that smelly farts can be a normal part of a healthy diet. But if you’re concerned, go to an expert before making radical changes. “The only sort of red flag is if there’s a sudden change and that doesn’t correspond with a sudden change in your diet,” Staller said.