Why do farts smell so bad, and how to remedy it

Flatulence, or passing gas, is a natural occurrence for everyone. Although uncontrolled or odorous flatulence may cause embarrassment, it results from the normal metabolic process in the digestive system. The gut microbiota breaks down dietary components in the large intestine, releasing gas.

Understanding gas production in the body

Gas in the digestive tract can be caused in two ways. One is the result of swallowing air, which usually leads to belching. The other is the result of the breakdown of food by naturally occurring bacteria in the large intestine, which can cause abdominal distention or flatulence in the passage of intestinal gas (flatus) through the rectum. The average person generates up to 1.5 L of gas daily, primarily composed of odorless gasses due to hydrogen, carbon dioxide, and methane. Less than 1% of intestine gas volume comprises gasses associated with an unpleasant odor resulting from sulfur-containing trace gasses like hydrogen sulfide. The good news is most causes of smelly flatulence are harmless and can be tied back to certain foods or medications, but in rare instances, they can be an indicator of a more serious underlying infection of the GI tract, digestive issue, or medical condition like colon cancer.

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Reasons why some farts smell so bad

Foods

Most foods that contain carbohydrates cause gas, while fats and proteins cause little gas. The stomach and small intestine do not fully digest certain carbohydrates, which then pass into the large intestine undigested. In the large intestine, undigested carbohydrates are broken down by naturally occurring bacteria, known as gut flora, which go on to release certain gasses. Other types of bacteria take in hydrogen gas and can produce sulfur gas, which is responsible for flatulence. The result? Smelly farts.

Foods that cause gas include the following carbohydrates:

• Raffinose: A complex sugar found in beans, and leafy greens, including cabbage, brussels sprouts, broccoli, asparagus, and whole grains.
• Lactose: A natural sugar found in milk and dairy, including cheese, yogurt, ice cream, and processed foods like bread and salad dressings. 
• Fructose is a sugar found in onions and artichokes and a sweetener in soft drinks and fruit drinks.
• Sorbitol: A natural sugar in fruits like apples, pears, peaches, and prunes; also used as an artificial sweetener in many sugar-free candies and gums.
• Starches: Potatoes, corn, noodles, and wheat generate gas during colon breakdown, whereas rice, being a starch, similarly does not contribute to gas production.
• Soluble fiber: Fiber that dissolves easily in water, found in oat bran, peas, beans, and many fruits, is known as soluble fiber.
• Insoluble fiber: Fiber that passes almost entirely unchanged through the intestines but produces little gas, including that found in wheat bran and vegetables like cauliflower.

Some foods contain sulfites, which can worsen the smell of normal flatulence. Foods containing sulfites include:

• Alcohol
• Eggs
• Garlic
• Nuts
• Onions
• Protein powders, including cysteine in whey powder, which is a sulfur-containing amino acid

Fiber-rich foods will naturally cause gas to occur. Therefore, consumption of a high-fiber diet could be the root cause of smelly gas. Intolerances to food due to a sensitivity or complete intolerance, such as gluten in celiac disease, could also cause smelly gas. 

Intestinal Disorders

Bacterial density in the small intestine is generally controlled and low density. Especially in comparison to the density of bacteria in the large intestine. However, certain conditions promote small intestinal bacterial overgrowth, which is a bacterial imbalance in either an increase in the density of bacteria or a change in the types of bacteria. These bacteria have the potential to cause excess gas. This type of bacterial overgrowth can result from diseases or disorders that damage the digestive tract, like Crohn’s disease, or irritation of any part of the digestive tract, like diabetes. Constipation can cause a back up of stool in the colon, contributing to noxious flatulence. Inflammatory bowel diseases (IBD), which include the autoimmune diseases Crohn’s disease and ulcerative colitis, or the chronic syndrome of irritable bowel syndrome (IBS), can also be the main reason for foul-smelling gas. In the rarest of cases, excessive and smelly gas can be a marker for colon cancer. This is why any new digestive issues or bowel movement changes warrant a healthcare provider evaluation. Colon cancer develops as polyps in the colon, and sometimes rectum, which can obstruct the bowel resulting in symptoms like bloating and foul-smelling gas. An evaluation for colorectal cancer without additional concerning signs and symptoms would likely be a later part of an evaluation for smelly farts and might include a colonoscopy. 

Medications

Medications can cause excess gas, which may also be stinky. Antibiotic courses can result in smelly gas because while they’re eliminating harmful pathogens, they’re nonselective and eliminate beneficial bacteria throughout the gut. Additional medications that can cause excessive or odorous flatulence include non-steroidal anti-inflammatory drugs (NSAIDs), antifungal medications, statins, and some laxatives. 

Other considerations include awareness of medical conditions, such as those with celiac disease and gluten intolerance, which can make certain medications a cause for concern for smelly gas, like consumption of medications that may contain gluten. It’s important for individuals with celiac disease to be aware of how to identify gluten-free drugs. 

Infection

Bacterial infections within the gut can also cause foul-smelling gas, usually in conjunction with other new physical symptoms like abdominal pain, diarrhea, fever, and fatigue. The sudden onset of smelly gas paired with other symptoms of acute illness can indicate an underlying infection and require immediate medical attention.

How to reduce smelly farts

People can attempt to identify the cause of stinky farts on their own by keeping a food journal of what they eat and how often they experience belching and flatus, or any other symptom. Seek medical advice if bothersome symptoms persist, change suddenly, or occur abruptly, especially in those aged 40 or older. Consult a healthcare provider if new symptoms such as constipation, diarrhea, or weight loss accompany gas.

Dietary modifications

Keeping a food diary to review the amount of burping or gas passed may help relate specific foods to symptoms and severity. If milk or other dairy products are causing gas, one might be evaluated further for lactose intolerance. Gluten sensitivity or celiac disease may also cause smelly gas and could be initially reviewed by eliminating gluten-containing foods for a brief period of time to see if symptoms resolve. In gluten sensitivity, foods containing gluten should be avoided, whereas in celiac disease, gluten must be avoided as exposure can cause damage to the gut over time. High-fiber foods, such as cruciferous vegetables like broccoli, brussels sprouts, and cabbage, can be difficult for the body to digest. The slow digestion process allows food to ferment in the digestive tract, producing odorous gas. 

Lifestyle changes

A few small changes can really make an impact on preventing excessive gas with a foul odor, including:

• Avoiding soda and carbonated beverages, which cause you to swallow air and develop gas
• Drinking sufficient water to prevent constipation
• Avoid eating excess fiber
• Do not chew gum or smoke to avoid swallowing air
• Consuming probiotics or eating foods that contain probiotics, like kimchi or yogurt
• Slow down eating by eating less, more often throughout the day; take your time chewing and swallowing the food

Taking over-the-counter gas medications  

The solution for managing too much foul gas is best approached by a doctor to determine the proper treatment. However, there are some manageable treatment options. Food intolerances are best managed by taking the path of least resistance, which may be simply to avoid those foods determined to result in the discomfort of flatulence. The benefits of those foods in the diet, such as lots of fiber-rich foods that have known health benefits, may be managed by consuming over-the-counter digestive aids like gas-relieving medications. For those with lactose sensitivity, making good food choices to avoid the development of severe abdominal cramps and foul-smelling flatulence, in addition to consuming lactase pills, is another option.

Home remedies for smelly gas

Peppermint tea or the consumption of other peppermint-containing products may be a way to reduce smelly gas. Peppermint aids digestion and relieves upset stomachs by relaxing muscles, facilitating gas passage, and promoting quicker food movement through the digestive tract.