The Smelly Fart Myth That's Actually Backed By Science

Farting is simply a fact of life whether we like it or not (by "like," we mean "find humorous"). While burping is the bodily function astronauts can't do in space, passing gas through the rectum is still possible. It actually occurs more than 20 times per day for the average person. Among the many other facts about flatulence are what some people think are fart myths but are actually based in science. For instance, there's a scientific reason silent farts often smell worse than loud ones.

Farts contain a combination of gases. As ModernGut founder and gastroenterologist Wendi LeBrett explains in a TikTok video, loud farts primarily contain carbon dioxide, hydrogen, oxygen, and nitrogen. All of these naturally occur in the air and are odorless, and they can end up in farts from swallowing air or from your body digesting certain carbohydrates. Along with these characteristics, loud farts aren't likely to stink because the gases pass quickly through the rectum. The reason these farts make a loud sound is because of their large volume, which makes the sphincter vibrate as it passes through.

On the other hand, silent farts are generally the result of fermentation in the gut, so they primarily contain methane and sulfur. Methane is odorless but slows how fast food moves through the digestive system, while sulfur is the main culprit behind the stink — and it doesn't take much for the nose to detect it. Along with silent farts passing through the rectum slowly, they don't make a sound because they're small in volume.

While science backs up the belief that loud farts don't stink as bad as silent farts, there are a couple of reasons that loud farts can smell. Consuming a lot of foods that are rich in sulfur compounds is one of them. Examples can include eggs, garlic, onion, red meat, and cruciferous vegetables — like broccoli, Brussels sprouts, cabbage, cauliflower, and kale. No matter how fast or slow the gases move through the digestive system, eating enough of these foods can produce smelly farts.

Another cause of loud, stinky farts is an underlying food sensitivity or gastrointestinal condition. As a functional gastrointestinal disorder, a sensitivity to FODMAP-containing foods can cause bloating and increased gas production in the intestines. FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) are short-chain carbohydrates, such as lactose in cheese and milk, fructose in certain fruits, soluble plant fibers in beans and wheat, and sugar alcohols in artificial sweeteners and some fruits. The small intestine can't break down the molecules of fermentable short-chain carbohydrates. When the intact molecules reach the large intestine, the gut bacteria ferment them, producing fatty acids and gases to which some people are sensitive.

Additionally, other gastrointestinal conditions such as celiac disease, inflammatory bowel disease, and irritable bowel syndrome can cause farts that smell bad. Colon cancer, a health issue increasing in Gen Z and millennials, can even cause persistent, smelly farts, which is why it's important to see a physician if such a symptom is a new development.