- Poop gets its odor from bacteria, your diet, and skatole — a compound in your digestive tract.
- Antibiotics, sulfur-rich foods, and difficulty absorbing nutrients can make your poop smell worse.
There's no way around it — poop pretty much stinks for everyone.
Skatole, a compound present in your digestive tract, plays a part in the pungent odor. But you can also thank a few other contributing factors, including:
- Your natural gut bacteria
- Bacteria from dental plaque that moves through your digestive tract
- Your diet, since certain foods can affect the odor of your stool
A new and unusual smell to your stool can happen for several reasons, from eating something new to an underlying health condition. Health experts point to these six culprits as the most likely causes of a sudden change in stool odor.
1. Antibiotics
Antibiotics help your body kill off as many bacteria as possible, but they don't distinguish between the "good" and the "bad" varieties.
This can sometimes create issues when it comes to your poop because it's the so-called good gut bacteria that help you digest food and give your stool its usual odor and consistency.
Taking antibiotics that kill good and bad bacteria alike, then, can disrupt your digestive system and can cause stinky stool and diarrhea — though experts have yet to determine exactly why this happens.
This imbalance in gut bacteria may also lead to inflammation and intestinal permeability, says Trista Best, a nutrition professor and registered dietician at Balance One Supplements.
Note: Research on intestinal permeability remains in the early stages, but some experts believe your gut bacteria may play a role.
Additional side effects you might notice while taking antibiotics include:
- Nausea or vomiting
- Bloating
- Reduced appetite or unintentional weight loss
- Stomach pain
- Change in stool color and consistency
What to do about it: Eating more probiotic foods can help restore your healthy gut flora, both while taking antibiotics and after you've finished your antibiotic course.
"Some of the most probiotic-dense foods include yogurt, kefir, sauerkraut, pickles, apple cider vinegar, miso, and kimchi," Best says. You can also try over-the-counter probiotic supplements.
2. Lactose intolerance
Trouble digesting dairy is more common than you might think — roughly 30 million Americans experience lactose intolerance by their twenties.
Lactose intolerance isn't a dairy allergy — it happens when your small intestine doesn't make enough of an enzyme called lactase.
When your body can't produce enough lactase, your digestive system can't break down the lactose in dairy products.
If you're lactose intolerant, you might notice the following within two hours after eating dairy:
- Nausea or vomiting
- Bloating
- Stomach pain
- Diarrhea
Over time, you may notice other symptoms, such as a reduced appetite or unintentional weight loss.
What to do about it: Cutting dairy from your diet offers the quickest fix, though you can also try taking over-the-counter lactase enzyme supplements when eating dairy.
But since the symptoms of lactose intolerance can resemble symptoms of other medical conditions, like irritable bowel syndrome, it's always worth connecting with a healthcare professional.
A doctor may recommend a lactose-hydrogen breath test, lactose tolerance test, or check the pH of your stool to confirm or rule out lactose intolerance
3. A high-sulfur diet
You can often trace foul-smelling stool and excess gas back to a sulfur-rich diet, says Krista Elkins, a paramedic and registered nurse specializing in treating people seeking emergency care for bowel issues.
Note: Sulfur compounds create the hallmark flatulence smell that may also accompany your stool.
Foods high in sulfur include:
What to do about it: Sulfur-containing foods make up an essential part of a balanced diet, since they protect your cells by reducing inflammation.
While it's not a good idea to fully cut sulfur from your diet, you can try cutting back on sulfur-rich foods before an event, if you want to avoid excess gas. A dietician or gastroenterologist can also offer more specific guidance on finding the right sulfuric intake for your dietary needs.
4. Nutrient malabsorption
Malabsorption, which happens when your body can't effectively absorb nutrients from the foods you eat, can cause foul-smelling stool and other health concerns.
If your body doesn't get the nutrients it needs, you may notice:
- Frequent diarrhea
- Unintentional or sudden weight loss
- Bulky stools
- Stool that floats in the toilet bowl and appears greasy or light-colored
- Bloating and gas
What to do about it: Malabsorption can suggest a number of health issues ranging from lactose intolerance to parasitic infections, so it's a good idea to reach out to your doctor as soon as possible to get the right diagnosis and explore possible treatments.
They can recommend tests or refer you to a specialist, who can help identify underlying causes, like food intolerances. A specialist can also recommend treatments or strategies to manage your symptoms.
5. Celiac disease
If you have celiac disease, eating even tiny amounts of gluten can trigger a severe immune response where your immune system attacks your intestinal lining.
Along with foul-smelling stool, fatigue, and unintentional weight loss, this condition can cause a number of digestive symptoms, including:
- Gas
- Bloating and abdominal pain
- Nausea and vomiting
- Constipation
- Diarrhea
If left untreated, celiac disease may eventually cause:
- Damage to your intestinal tract
- Joint pain
- Headaches
- Anemia
- Osteoporosis
- Celiac hepatitis
- Mental health symptoms, like anxiety and depression
What to do about it: The only known treatment for celiac disease involves cutting gluten out of your diet permanently. You'll also want to check your medications and anything you could potentially ingest, like lipstick, for compounds that contain gluten.
If you've noticed other symptoms of celiac disease in addition to foul-smelling stool, you may want to make an appointment with a gastroenterologist. They can recommend tests, like an endoscopy and a blood test, to help pinpoint the cause of your symptoms.
6. Blood in your digestive tract
Blood in your stool, which can come from your stomach, rectum, or other parts of your intestinal tract, may also cause changes in fecal smell.
The color and consistency of the blood can offer some insight into where it comes from:
- Bright red or pink may suggest bleeding in your colon.
- Deep red or brown may suggest bleeding in your upper colon or small intestine.
- Black or tarry stool may suggest bleeding in the upper part of your digestive tract, like the stomach or esophagus.
What to do about it: In some cases, bloody stool can suggest a serious infection, bleeding in major organs, or even cancer. So, if you notice blood in your stool, you'll want to make an appointment with a healthcare professional as soon as possible — or visit the emergency room.
A doctor may take a stool sample or recommend other tests, like an endoscopy or colonoscopy, to pinpoint the cause of blood in your stool.
When to connect with your doctor
Elkins says you'll want to reach out to a healthcare professional immediately if you notice a sudden change in fecal smell accompanied by severe abdominal pain, diarrhea, or blood in your stool.
Sudden changes in your stool can happen due to an infection, bowel obstruction, or cancer, Elkins says, and these conditions often require immediate treatment.
Chronic conditions that cause unusual stool smell, like food intolerances and celiac disease, may also require regular follow-ups with your care team.
Quick tip: You can also try keeping a food journal to help you and your doctor track any patterns connecting stool and your diet. This log may include food descriptions and a Bristol Stool Chart for tracking stool consistency, along with notes on any symptoms, pain levels, or smells you notice.
Insider's takeaway
Anything from changes in your diet to underlying health conditions can make your bowel movements smell much worse than usual, Elkins says.
If you experience severe pain or diarrhea along with a new and unpleasant stool smell, seeking immediate medical help is your safest option.
Treatment for any underlying medical conditions, along with a few dietary changes, can help restore your gut health — which means your poop will go back to business as usual.