Sewer-like stool smell usually comes from bacterial overgrowth in your digestive tract

When your stool smells like sewer gas, the culprit is almost always hydrogen sulfide — a gas produced when bacteria in your colon break down food, especially proteins and sulfur-containing compounds. This is normal in small amounts, but an overgrowth of certain bacteria or a change in your gut environment can make the smell much stronger and more unpleasant.

The smell becomes noticeable when you have fewer beneficial bacteria to balance the process, when food moves through your digestive system too slowly, or when you eat foods that feed the bacteria that produce sulfur compounds. Unlike a one-time bad smell after eating something unusual, a persistent sewer-like odor usually signals that something in your digestion has shifted.

Key Takeaways

  • Hydrogen sulfide gas from bacterial overgrowth is the main cause of sewer-like stool odor, and it becomes stronger when beneficial bacteria are depleted.
  • Constipation, high-protein diets, and foods like eggs, meat, and cruciferous vegetables feed sulfur-producing bacteria and intensify the smell.
  • Antibiotics, digestive disorders like IBS or SIBO, and inflammatory bowel disease can all disrupt your gut balance and trigger the odor.
  • Increasing fiber, drinking more water, and eating fermented foods may help restore bacterial balance, but persistent odor lasting more than two weeks warrants a conversation with your doctor.

Foods and eating patterns that make stool smell worse

High-protein meals are the most common dietary trigger. When you eat large amounts of meat, eggs, or fish, your colon bacteria ferment the undigested protein and release hydrogen sulfide as a byproduct. This is why people on very low-carb or high-meat diets often notice stronger odors.

Cruciferous vegetables like broccoli, cabbage, and Brussels sprouts contain sulfur compounds that bacteria break down into smelly gases. Garlic and onions do the same thing. If you eat these foods in large quantities or your digestion is already slow, the smell intensifies because the food sits in your colon longer.

Constipation makes any stool smell worse because slower movement gives bacteria more time to produce gases. If you are not having regular bowel movements, increasing water intake and adding soluble fiber (oats, beans, apples) can help move things along and reduce the time bacteria have to work.

Digestive conditions that cause sewer-like odor

Small intestinal bacterial overgrowth (SIBO) is a common cause of persistent foul-smelling stool. In SIBO, bacteria that normally live in your colon migrate into your small intestine, where they ferment food too early in digestion and produce excess gas. The smell is often described as rotten or sewage-like.

Irritable bowel syndrome (IBS) can trigger the odor because it disrupts how fast food moves through your system and changes which bacteria thrive in your gut. People with IBS often report that their stool smell varies depending on stress, diet, and bowel movement frequency.

Inflammatory bowel disease (Crohn's disease or ulcerative colitis) damages the gut lining and allows harmful bacteria to flourish while beneficial bacteria decline. The resulting imbalance produces stronger sulfur smells. If you have bloody stools, severe cramping, or weight loss along with the odor, see a doctor soon.

Celiac disease and lactose intolerance both cause undigested food to reach your colon, where bacteria ferment it and produce gas. If the smell started after you began eating more bread, pasta, or dairy, these conditions may be worth exploring with your doctor.

How antibiotics and medications affect stool smell

Antibiotics kill both harmful and beneficial bacteria in your gut. After a course of antibiotics, your beneficial bacteria population drops sharply, allowing sulfur-producing bacteria to multiply unchecked. This is why antibiotic-related diarrhea and foul-smelling stool often appear during or shortly after treatment.

Other medications that slow digestion — including some pain relievers, antidepressants, and blood pressure drugs — can increase stool odor by giving bacteria more time to ferment food. If the smell started after you began a new medication, mention it to your doctor; they may be able to adjust your dose or switch you to an alternative.

Steps to reduce sewer-like stool odor

Start by drinking more water. Dehydration slows digestion and gives bacteria more time to produce gases. Aim for at least eight glasses a day, and more if you exercise or live in a hot climate.

Add fiber gradually — too much too fast can actually make gas worse. Soluble fiber (oats, beans, apples, carrots) feeds beneficial bacteria and helps stool move faster. Insoluble fiber (whole wheat, leafy greens, berries) adds bulk and speeds transit time. Increase by a few grams every few days to let your system adjust.

Eat fermented foods like yogurt, kefir, sauerkraut, or kimchi to restore beneficial bacteria. These contain live cultures that can help rebalance your gut. If you have IBS or SIBO, introduce them slowly because the initial fermentation can temporarily increase gas.

Reduce high-protein meals temporarily and spread protein throughout the day rather than eating large amounts at once. This gives your bacteria less material to ferment at any one time. You do not need to eliminate protein — just balance it with vegetables and whole grains.

Limit foods that trigger you personally. Keep a straightforward food diary for three to five days, noting what you eat and how your stool smells the next day. You will quickly see which foods make it worse for your body.

When to see a doctor about stool odor

A one-time foul smell after eating a heavy meal or trying a new food is normal and does not require medical attention. But if the sewer-like odor persists for more than two weeks despite dietary changes, or if it comes with other symptoms, contact your doctor.

See a doctor right away if you also have bloody stools, severe cramping, unexplained weight loss, or diarrhea lasting more than a few days. These can signal inflammatory bowel disease, infection, or another condition that needs treatment.

If you recently finished antibiotics and the smell has not improved after two weeks of eating fermented foods and increasing fiber, ask your doctor about testing for C. difficile infection, which can cause severe odor and diarrhea.

Your doctor can order tests to check for SIBO, celiac disease, lactose intolerance, or other digestive disorders. They can also review your medications to see if any are slowing your digestion.

Frequently Asked Questions

Is sewer-like stool smell a sign of a serious infection?

Not always, but it can be. Most of the time it is caused by diet, constipation, or a temporary bacterial imbalance. However, if the smell is new, persistent, and comes with diarrhea, fever, or bloody stools, contact your doctor to rule out infection or inflammatory disease.

Can probiotics help fix the smell?

Probiotics may help restore beneficial bacteria after antibiotics or during an imbalance, but the evidence is mixed and results vary by person. Fermented foods like yogurt and sauerkraut are often more effective because they contain live cultures in higher numbers. Talk to your doctor before starting a probiotic supplement if you have IBS or a weakened immune system.

Does drinking more water really help?

Yes. Dehydration slows digestion and gives bacteria more time to ferment food and produce sulfur gases. Drinking enough water helps stool move faster through your colon, reducing the time bacteria have to work. You should see improvement within a few days of increasing your intake.

Why does the smell get worse at night or in the morning?

Stool sits in your colon longer while you sleep, giving bacteria more time to produce gases. Morning stool often smells stronger for this reason. If the smell is much worse in the morning, try eating dinner earlier and drinking water before bed to keep things moving.

Can stress make stool smell worse?

Yes. Stress slows digestion and changes which bacteria thrive in your gut, both of which can intensify odor. People with IBS often notice their stool smell gets worse during stressful periods. Regular exercise, sleep, and stress management can help normalize digestion and reduce the smell.