Here’s Why Your Farts Smell So Bad, According to Science

Nobody likes to talk about farting. But gas production is a normal byproduct of digestion. In fact, most people toot an average of 8 to 14 times per day (sometimes even more).

Luckily, most farts are odorless, but not always. So, why do farts sometimes smell so awful, and what can you do about it? To find out, we asked digestive health experts to share their insights on what is going on behind the scenes, tricks to combat smelly farts and when to be concerned. 

What Causes Farts to Smell?

You Started Eating More Fiber

Fiber does all kinds of great things for your body, like preventing constipation, helping with weight management, regulating blood sugar and lowering cholesterol.  But if you suddenly start eating loads of it, things could temporarily get kind of stinky. “It’s pretty normal for the smell of your farts to change depending on the foods you’re eating, especially if you’re working on increasing your fiber intake,” says Amanda Sauceda, M.S., RDN. That’s because higher-fiber foods take time to digest, so as they sit in your gut, they begin to ferment. 

That doesn’t mean you shouldn’t eat fiber. “Your gut microbiome needs some time to adjust to the increased amount of fiber, which it uses as fuel and also produces gas as a result,” says Sauceda. Once your gut adjusts to your new eating pattern, things will likely start to calm down. In the meantime, try to increase fiber slowly rather than all at once. 

If you’re wondering if some high-fiber foods are more problematic than others, the answer is yes. For instance, functional fibers, like inulin, that are added to foods to boost their fiber content, can sometimes be to blame for smellier gas. One unlikely, yet trendy, place you’ll find inulin is in prebiotic sodas, says Sauceda. So, if you’ve recently started drinking prebiotic soda and your farts are smelling off, that might be the reason. 

You Eat Lots of High-Sulfur Foods

Another factor to blame for stinkier gas is sulfur-containing foods. “The pungent smell of passed gas is mostly due to sulfur-containing compounds that are produced when bacteria in your gut break down undigested food products,” says gastroenterologist Adam Pont, M.D. “[While] this is a normal part of digestion, the odor intensity may increase if you eat foods high in sulfur.” And the list of sulfur-containing foods is long. Cruciferous veggies like cauliflower, broccoli, cabbage and arugula are all major offenders. So are eggs, ham, beef, chicken and fish., That’s not a reason to give them up though, especially since they’re packed with nutrients that do your body good. But if things are smelling off, try to ease back on the cruciferous veg a bit and add in more non-cruciferous veggies.

You Have a Food Intolerance

If you’ve noticed that your farts are especially pungent and are accompanied by other symptoms like bloating or diarrhea after you eat specific foods, you might have a food intolerance. For instance, some people are unable to fully digest lactose in dairy products or fructose from fruit and honey. Many people can eat these without issue. But if you have a lactose or fructose intolerance, you aren’t able to fully break down these sugars in the small intestine. Instead, they travel intact to the colon, where bacteria that live there break them down and produce excess and potentially foul-smelling gas. 

Just because you have a lactose or fructose intolerance doesn’t mean you have to avoid dairy or fruit entirely. “There are lower-lactose foods, like yogurt or hard cheeses, as well as completely lactose-free products,” says Sauceda. If fructose is an issue, try eating fewer high-fructose apples, pears, cherries, mangoes, figs and watermelon and opt for other fruits instead.

You’re Constipated

Constipation isn’t just uncomfortable. It can also cause smellier-than-normal farts. Common constipation symptoms include having less than three bowel movements per week or having stools that are dry, hard or difficult to pass. The problem is that when you aren’t pooping regularly, bacteria and odor can build up. Fortunately, making small adjustments to your diet and lifestyle can help tackle constipation and the stinky wind that comes along with it. For less constipation, try slowly upping your fiber intake, drinking more water, managing stress and incorporating movement into your day. 

You Have a Digestive Disorder

Gas and bloating are common symptoms of several digestive disorders like celiac disease and inflammatory bowel disease (IBD). But it’s not just about the amount of gas. “​​There is even thought that those with digestive disorders may remark on more stinky types of farts,” says Sauceda. “People with inflammatory bowel disease have remarked on more odor compared to those without IBD.” It’s not their imaginations, either. One study found that people with IBD really do have smellier farts, most likely due to unfavorable changes in their gut bacteria. 

Speaking of bacteria, you may also experience funky-smelling gas if you have a bacterial overgrowth called SIBO (short for small intestinal bacterial overgrowth). This can result in excessive fermentation and odor when bacteria produce gas while breaking down food, explains gastroenterologist Ritu Nahar, M.D.

When to Be Concerned

“While occasional bad-smelling gas is normal, there are a few signs that may warrant medical attention,” says Nahar. “If the foul odor is persistent and accompanied by other symptoms like bloating, diarrhea, unintentional weight loss or fatigue, it could indicate an underlying condition such as celiac disease, inflammatory bowel disease or a gastrointestinal infection.” An unusually strong or constant odor without any change in diet is also cause for concern, she says. “In those cases, it’s a good idea to check in with a health care provider to rule out more serious digestive issues,” she advises.

Our Expert Take

Tooting is a normal and healthy part of digestion. While most farts are fairly odorless, there are times when you may notice that they are a bit more pungent. Don’t panic! Smelly farts can be caused by a variety of factors, like eating more fiber- or sulfur-rich foods. They can also be the result of food intolerances, digestive disorders and even constipation. While digestive health experts say the occasional foul-smelling fart is nothing to worry about, you might want to follow up with your health care provider if you also start experiencing other symptoms like diarrhea or weight loss. Otherwise, small tweaks like easing up on fiber or eating smaller servings of cruciferous veggies, eggs, dairy, meat, chicken and fish or avoiding high-fructose fruits may help.