What Causes Smelly Farts? Top 4 Reasons & What to Do

Smelly farts can be caused by excessive intake of foods with high amounts of protein and fiber, like eggs, broccoli, cauliflower, red meat, garlic and cheese. These foods are more likely to produce hydrogen sulfate, which has a distinctive "rotten egg" smell. This substance is produced by intestinal bacteria during the fermentation phase of digestion. 

Foul-smelling flatulence can also be caused by some medications, food poisoning, constipation, irritable bowel syndrome, lactose intolerance and colon cancer. 

Some ways to prevent smelly farts include chewing your food thoroughly, drinking tea like mint and fennel, and decreasing intake of foods with sulfur and fiber. These measures help to promote digestion.

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The main causes of smelly farts are:

1. High protein food

Excessive intake of high protein food, like milk, cheese, yogurt, red meat, fish and eggs, can increase the production of hydrogen sulfate by intestinal bacteria. This substance is what gives gas a smelly odor. 

What to do: Eat smaller portions of protein throughout the day. You should aim for about 1 g of protein for each kg (or 2.2 lb) of body weight per day. For example, someone who weights 85 kg should consume 85 g of protein per day, which is equivalent to 150 g of baked chicken breast and 100 g of grilled sardines. See our list of high protein food to get an idea of protein quantities in common, day-to-day foods.

2. High fiber food

Foods that are high in fiber and sulfur, like broccoli, cauliflower, asparagus, onions, parsnip and brussel sprouts, are likely to produce smellier farts. 

Although they do not directly affect gas formation, some fiber-rich foods, like beans, soy beans, lentils, oats, asparagus, apples, and almonds, can take longer to be digested. This can increase the fermentation period, leading to increased gas. Learn about other foods that cause gas and bloating

What to do: You should decrease intake of vegetables with sulfur. You should also reduce consumption of fruits and vegetables with high quantities of fiber. It is important to highlight, however, that fiber is important for health and wellbeing, and you should only aim to reduce fiber intake when you are experiencing too much gas. Learn more about high-fiber foods that you can add to your diet. 

Read more about what can cause excess gas and how to treat it. 

3. Gastrointestinal problems

Some gastrointestinal problems, like constipation, diarrhea, food poisoning, irritable bowel syndrome, lactose intolerance, celiac disease and colon cancer, can lead to an imbalance in intestinal flora. This can result in increased formation of gas, particularly foul-smelling gas. 

What to do: In these cases, you should be thoroughly by a doctor to determine the underlying cause of the gas. The doctor may recommend specific treatment that can address the gas and other related symptoms. Check out these home remedies for gas that you can use as a complement to your medical treatment. 

4. Medications

Some medications, like antibiotics, anti-inflammatories and laxatives, can modify intestinal flora by affecting the amount and types of bacteria present. These factors can lead to increased production of smelly farts. 

What to do: To increase levels of good bacteria in the gut and to strengthen them, you should incorporate probiotic food into your diet, like kefir, kombucha and Greek yogurt. These help to keep intestinal flora levels balanced, which can prevent foul-smelling farts. 

Read about the other health benefits of kombucha and how to drink it.