6 Causes of Foul-Smelling Stool
Nobody’s stool smells good. But if the odor is different or worse than usual, it could be a sign of a problem.
Your stool is a product of several things, including your diet, colon health, and your overall health. It’s also a product of your digestive system microbiome. That is made up of microbes (bacteria) that live in your gut.
Most of the time, smelly poop is caused by your diet. It could be caused by eating certain foods or from lactose intolerance. But if it routinely smells bad, you may have an imbalance in your microbiome or a disease like inflammatory bowel disease.
Occasional foul-smelling stool may not require any treatment. But if it continues or you also have other symptoms, like runny stool, more frequent bowel movements, nausea, vomiting, or stomach pain—see your doctor.
1. Dietary changes
Just because your stool smells really bad after eating particular foods does not mean you have to cut out those foods. As long as you are not having other symptoms with it, foul-smelling stools on their own are not a problem. —Dr. Shria Kumar
- Foul-smelling stool every so often
- Abdominal pain
Eating foods that don’t agree with you (such as dairy if you’re lactose intolerant), or foods that smell bad (asparagus, durian) can all lead to foul-smelling stools. If your stool smells really bad a few times in a row, it’s likely that it’s because of a food that you ate.
If you are lactose intolerant, avoid dairy foods or take a supplement with lactase enzymes before eating dairy foods. If symptoms continue or you also have severe pain or fevers, see your doctor to rule out other conditions.
2. Irritable bowel syndrome
- Foul-smelling stool
- Abdominal pain
- Changes in stool (diarrhea or constipation)
The most common symptom of IBS is stomach pain. Some people with IBS say they experience a bad odor and changes in stool.
If you suspect you have IBS, see your doctor. Although there is no cure for IBS, there are many treatments available to help control your symptoms. Medications include anti-spasmodics (for belly pain and cramps), gut-specific antibiotics for diarrhea, and other medications.
- Loose stools while you’re taking antibiotics and for a few weeks after you stop
- Foul-smelling stool
Antibiotics can change the balance of your gut microbiome (mix of bacteria in your gut). This can cause changes in the odor of your stool and its consistency.
These side effects of antibiotics are usually temporary. They either stop after you complete your antibiotics or within 2 to 4 weeks. It’s not usually a cause of concern.
If your symptoms continue and bother you, your doctor may suggest taking probiotics. Your doctor may also recommend treatments similar to those for IBS, such as medications that relieve diarrhea.
- Foul-smelling stools
- Abdominal pain and cramping
- Rectal pain
- Increased urgency or need to defecate
- Loss of appetite
Gastrointestinal (GI) infections have many causes, including bacteria, viruses, or parasites. If you have an infection, you’ll usually also have other symptoms, such as diarrhea or abdominal pain.
See your doctor, who will do tests to identify what caused your intestinal infection.
If it’s a bacterial bug, your doctor will likely prescribe antibiotics. If you have a parasite, they may give you an anti-parasitic medication. If it’s viral, there is nothing to cure the illness. Treatment will focus on staying hydrated and resting.
5. Inflammatory bowel disease
Our stool is a product of multiple factors: our diet, our colon health, body health, and our microbiome (all the microbes that live on and inside the human body). This is a relatively hardy system, but changes in the balance can result in changes in our stool. —Dr. Kumar
Inflammatory bowel disease (IBD) is an inflammation of the digestive tract. There are two types of IBD: Crohn’s disease and ulcerative colitis. Symptoms may develop gradually or they can occur suddenly.
IBD is caused by several factors, including genetics. If you have a parent or sibling with IBD, you have a higher risk of developing it as well. Lifestyle plays a role too. For example, people who smoke are more likely to develop Crohn’s disease.
If you suspect you have IBD, see your doctor. Left untreated, IBD can lead to serious problems, such as malnutrition, bleeding, certain cancers, and overall poor health.
Your doctor should refer you to a gastroenterologist (specialist in digestive diseases) and will do tests to confirm a diagnosis. The goal of treating IBD is to eliminate inflammation so the disease goes into remission (symptoms stop).
This is typically done with medication and changes to your diet. Most people with IBD will have recurrence of symptoms (“flares”). If these are severe, surgery may be required to remove parts of the bowel.
6. Celiac disease
- Oily, foul-smelling stool
- Chronic diarrhea
- Stomach bloating
- Weight loss
Celiac disease is an autoimmune disease that causes inflammation in your digestive tract. In people with celiac disease, eating gluten, a protein found in wheat, rye, and barley, triggers the immune system to respond. The inflammation damages the lining of the small intestine.
See your doctor if you think you have celiac disease. It is treated mostly by avoiding products that contain gluten. Your doctor will also recommend regular blood tests to check for nutrient deficiencies. This is because the inflammation caused by celiac can make it difficult for your body to absorb the nutrients in food.
Other possible causes
A number of conditions may also cause foul-smelling stool, but it is usually not the main symptom or they’re not very common.
- Internal bleeding
- Cystic fibrosis
- Pancreatic insufficiency
- Colon cancer
Why does my infant have foul-smelling stool?
Babies may have foul-smelling stool for a variety of reasons. They could have a stomach infection, or it may be a sign of something more serious, such as celiac disease or cystic fibrosis. It could also be the result of a vitamin deficiency.
Call your pediatrician if it persists. They may ask you to track when the foul-smelling stool began, any color changes, and how often your infant poops.
When to call the doctor
Ask your doctor: What triggered this? Is there any testing I need, based on my history and symptoms? —Dr. Kumar
See your doctor if you have foul-smelling stool and:
- Very pale stool
- Weight loss
Should I go to the ER for foul-smelling stool?
You should go to the emergency room if you have any of the following:
- Black, tarry stools or blood in stool
- High fever
- Severe pain
- Drink more water to keep waste moving through your system and improve digestion and absorption of nutrients.
- Keep a food diary so you see if a certain food you eat is causing foul-smelling stools.
- Eat more foods rich in naturally occurring probiotics, like fermented foods and yogurts, to keep your gut microbiome balanced. Eating fiber-rich foods like fruit and vegetables will also help.
- Stop smoking or drinking alcohol, which can irritate your GI tract.
Other possible treatments
- Medications to treat any underlying infections (i.e., antibiotics for a bacterial infection).
- Diagnostic tests for IBS or other diseases (such as blood work or an endoscopy).
- Medications to treat symptoms, such as anti-diarrheal or antispasmodic drugs to help relieve symptoms.
Dr. Kumar is a gastroenterologist, who completed her fellowship at the Hospital of the University of Pennsylvania in Philadelphia. She received her undergraduate degrees in Religious Studies and Chemistry from New York University (2010) and graduated from the Albert Einstein College of Medicine (2014), where she was inducted into the Alpha Omega Alpha Honor Medical Society. She is completing her therapeutic endoscopy fellowship at MD Anderson Cancer Center in Houston. She joined Buoy Health in 2020. She believes in the importance of patients being educated about their health, and joined Buoy in order to be part of a platform that helps disseminate clear and verified advice directly to patients.