Why Do Your Farts Smell Foul? Common Causes of Stinky Farts

Passing gas, farting, or cutting the cheese. No matter what you call it, everyone does it. On some days, people fart more than others. And on other days, farts are smellier — and those days can be embarrassing. But what causes the smell to change?  

In this article, we search for answers to some of life’s most embarrassing questions. We discuss the causes of smelly farts — and what you can do about them. 

What are farts and why do they smell?

Flatus and flatulence are the official medical words for farts and farting. Farts are made up of common gasses like hydrogen, methane, and carbon dioxide. These gasses aren’t toxic — they’re found in the air you breathe. 

Gasses enter the gastrointestinal (GI) tract in three different ways:

• Swallowing air: Air is sucked into the lungs when you inhale, but some also enters the stomach. Eating or drinking too quickly, chewing gum or tobacco, and drinking fizzy beverages can increase the amount of air that enters the stomach.

• Creation of gas by bacteria in the colon: Healthy bacteria (normal gut flora) live in the colon and help digest food. The digestion process produces gasses. Certain foods are harder to digest than others, and some foods create foul-smelling gasses when broken down.

• Movement of air from the bloodstream to the bowel: A very tiny amount of air moves from the blood into the bowels. The amount is so small that it almost doesn’t count.

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What causes farts to smell bad?

Most farts actually don’t smell at all. That’s because hydrogen, methane, and carbon dioxide — the main gasses that make up farts — don’t have odors. 

What about farts that smell like sulfur or rotten eggs? Flatulence that’s so stinky it clears out the room? In these cases, another gas is present — hydrogen sulfide. Hydrogen sulfide is a colorless gas that smells like rotten eggs. It’s produced in small amounts by some bacteria in the gut. So most of the time, stinky farts are the result of normal digestion of certain foods. 

But everyone’s gut flora are different, and some people just have smellier farts than others. 

Other causes of extra stinky farts include:

• Medications: Antibiotics are notorious for causing an upset stomach. They can disrupt the balance of “good” and “bad” bacteria in the gut, which can lead to foul-smelling farts. 

• Constipation: A traffic jam of extra stool can add odor to gas as it’s passed.

• Menstrual cycle: Some people notice changes in their bowel movements, bloating, and excess gas when they have their period. Researchers think this could be due to alterations in the gut microbiome (bacteria) or changes in hormones. 

In rare cases, a more serious medical condition can cause the stink. But keep in mind, foul-smelling gas by itself is unlikely to be a sign of something dangerous. These conditions will usually have other symptoms like diarrhea or weight loss:

• Celiac disease (allergy to gluten)

• Small intestinal bacterial overgrowth (SIBO), or too much bacteria in the GI tract

• Giardia infection (a common parasite)

• Colorectal cancer (this is less likely without other concerning symptoms)

How can you stop smelly farts?

Generally speaking, stinky farts will go away once the cause has worked its way out of your system. To help prevent smelly flatulence in the future, consider making some changes to your diet.

The following foods increase the amount of gas and smelliness of farts:

• Beans, lentils, and bean-based products (like hummus, tofu, and tempeh)

• Certain vegetables (like brussels sprouts, broccoli, cabbage, and cauliflower)

• Certain fruits (like prunes and apricots)

• Beer

• Foods high in fiber (like whole grains)

• High-protein foods (like animal meat) and powders (commonly used to build muscle)

• Dairy products from cow’s milk (if you have lactose intolerance)

• Artificial sweeteners in sugar-free foods (like xylitol and sorbitol)

• Fatty, fried foods

When something other than food causes smelly farts, the aim is to treat the underlying cause. For example, if your healthcare professional finds that you have SIBO, they’ll recommend treatment with antibiotics. You can treat lactose intolerance by avoiding dairy and/or taking lactase supplements to help the gut digest milk products. And if constipation is the problem, there are ways to deal with that, too.

Are there medications to decrease farting or the stinkiness of farts?

Unfortunately, no. Though it might be nice to get rid of farts entirely, farting is just a part of life. Most people pass gas about 10 to 20 times a day.  

Studies have shown that simethicone (GasX), activated charcoal, and alpha-galactosidase (Beano) aren’t very effective. Interestingly, there are odor-reducing products, such as underwear made out of activated carbon fiber fabric or charcoal pads you wear inside of underwear. They might help, but these aren’t widely available.

When should you see a healthcare professional for smelly farts?

Lots of gas or very smelly gas can be embarrassing. But it’s rarely a sign of cancer or other serious medical problem. When it comes to smelly farts or lots of farts, diet is most likely the culprit. But there are some symptoms that could raise concern for a bigger issue. 

Talk with your healthcare professional if you experience any of the following concerning symptoms:

• Fevers

• Unintentional weight loss or loss of appetite

• Bloody stools or dark black, tar-colored stools

• Severe diarrhea 

• Severe vomiting

• Severe abdominal tenderness

Your healthcare professional may ask you more questions, examine you, and possibly order some tests. Together you can come up with a plan to figure out what’s going on.

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

Reviewed by:

Christine Giordano, MD

Christine Giordano, MD, is board-certified in general internal medicine. She received her medical degree from Rutgers New Jersey Medical School and completed residency at Thomas Jefferson University.

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