Whether you call it farting, passing gas, breaking wind, or any other euphemism, flatulence is a natural bodily function that everyone has experienced. While the familiar (and yet highly variable) sound has been comedic gold for centuries, it’s the smell that people tend to find most objectionable. But not all farts smell bad, and in fact there can be a wide range of odors in varying levels of intensity. So why do farts smell bad? And why are they sometimes especially stinky farts?

What Is Flatulence?

Flatulence is the medical term for the expulsion of intestinal gasses through the anus; this gas, known as flatus, is often trapped in the digestive system after swallowing air, usually during eating. Gas may also be the result of the chemical reactions that occur as food is broken down in the stomach and intestines. Some types of food are more likely to result in gas when consumed, though each individual’s body may react in a different way depending on food combinations, quantity, and timing.

What Causes Smelly Farts?

Even though it can be humorous or embarrassing, passing gas is quite normal and something that typically happens many times a day. Most of the time farts are silent and odorless, but they can also develop a smell that can be described as sulfuric or like rotten eggs. Flatus is generally some combination of several different gasses: nitrogen, oxygen, carbon dioxide, methane, and hydrogen sulfide. The specific combination of gasses and character of the odor can be due to a variety of factors

  • Bacteria: The digestive tract is home to a microbiome of helpful bacteria that serve many functions in the process of digestion, and their activities are also one of the main reasons for why farts might smell bad. These bacteria can have a different effect on different kinds of foods, and gas is a natural byproduct. In fermentation, for example, bacteria consume carbohydrates and produce ethanol and carbon dioxide. While this is a natural process, disruption to the microbiome (as in bacterial overgrowth) can cause an even greater amount of gas.
  • High fiber: Some foods that are high in dietary fiber can cause an increase in intestinal gas. This is primarily because they take longer to digest and have more time to ferment in the digestive tract. Examples include Brussels sprouts, lentils, broccoli, and cabbage. Some high-fiber foods are also high in sulfur content that can create a particularly stinky gas.
  • Food allergy or intolerance: People who are allergic to certain foods or are sensitive to certain foods are often more likely to have smelly farts. A classic example is lactose intolerance; a lack of the enzyme lactase means that lactose from dairy products can’t be digested. This then allows the lactose to be fermented by bacteria in the digestive tract that in turn causes a release of gas. Celiac disease and other gluten disorders can also be a source of smelly farts, though in this case it is due to an inflammatory reaction to the protein gluten.
  • Constipation: Constipation is typically defined as having fewer bowel movements than normal along with having poop that is dry or hard to pass. Constipation is also a possible cause of gas. This is because poop sits in the colon for longer than normal, giving bacteria more time to react to the contents and generate more gas. Depending on the composition of bacteria and a person’s diet, constipation can lead to especially smelly farts.
  • Disease: Even though they are typically a mild—if unpleasant—inconvenience, there are some health conditions that include smelly farts as a sign or symptom. Examples include bowel obstructions, an inflammatory bowel disease (like Crohn’s disease), irritable bowel syndrome, or colon cancer.
  • Medication: Though not the most common cause of smelly farts, certain medications can sometimes be the culprit. This is particularly true with medications that affect the microbiome like antibiotics. Antibiotics are designed to kill the harmful bacteria that can lead to various diseases, but sometimes in killing harmful bacteria, the helpful bacteria we rely on is also killed. This imbalance can cause changes to digestion that ultimately result in stronger odors in the flatus.

When Are Smelly Farts a Concern?

As noted, flatulence in general is a common phenomenon that almost everyone will experience at some point. For the most part, flatulence—regardless of the intensity of smell—isn’t a cause for concern, especially because swallowing air is one of the most common reasons for a buildup of gas. Even farts with a truly foul-smelling gas are most likely benign. In rare circumstances it can be a sign of a deeper problem, but in such cases the odor will usually be accompanied by other gastrointestinal symptoms like cramps, abdominal pain, bloating, nausea, vomiting, diarrhea, incontinence, or bloody poop.

How to Find Relief From Smelly Farts

Gas that is trapped in the body needs to escape one way or the other, so there’s no way to completely prevent farting. There are a few steps you can take to reduce the likelihood of really smelly farts, however:

  • Eat smaller portions of a food at a slower pace; this encourages healthier digestion and may also decrease the amount of air swallowed while eating.
  • Look for patterns in the occurrence of smelly farts after eating certain foods. You may have a food intolerance that you weren’t aware of, and by eliminating or limiting the food you can reduce gas.
  • Be wary of artificial sweeteners like sorbitol that are known to cause gastrointestinal symptoms in some people, including smelly gas.
  • Many people don’t drink enough water throughout the day, but staying sufficiently hydrated is good for overall health as well as proper digestion.
  • There is some evidence that eating more probiotic foods like yogurt can have a beneficial effect on the gut bacteria; this in turn can improve digestion and make smelly gas less likely.
  • If you drink a lot of carbonated beverages, cutting back can help you lower the amount of gas that gets trapped in the digestive tract.
  • Over-the-counter digestive medications can help reduce gassy buildup as well as promote better digestion.
  • Regular physical activity and exercise are also generally beneficial for digestion and may decrease the chances of flatulence.

Contact a Gastroenterologist

Flatulence is a normal part of the digestive process that everyone experiences on a daily basis, and sometimes it can have a pretty unpleasant smell. The good news is that stinky farts are almost always not a concern (except maybe as a social faux pas). If you have a pattern of foul-smelling farts along with other gastrointestinal symptoms, however, it might be an indication of a larger problem. If you’d like to speak with a gastroenterologist about your symptoms, please contact us at Cary Gastro to request an appointment.