What causes poop to smell like chemicals?

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So let’s just get clear about this. Nobody’s poop smells great. So smelly poop is totally normal. But sometimes you might have poop that smells worse than your norm, especially if you ate something different than you usually do or started new medications.

The good news is smelly poop is typically harmless, except for the assault on your senses. Here’s why the bathroom might be so smelly and what you can do about it:

You’re eating foods high in sulfates

“The key thing that affects the smell of stool is diet. The food with which we fuel our system directly influences the bacteria in our digestive system and in our stool,” says Niket Sonpal, MD, a New York-based gastroenterologist and adjunct professor at Touro College. As food is broken down in the body, gases are produced as byproducts, and their smell can be pretty strong.

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Foods that are high in sulfate content such as veggies, dairy, eggs, and meat can cause poop that smells like rotten eggs. “Sulfur is a necessary component in our diet, and certain foods high in sulfates increase sulfur gas as the byproduct of foods being broken down,” he says. These include broccoli, Brussels sprouts, cabbage, cauliflower, and other cruciferous veggies. Sulfates are also found in eggs, dairy, arugula, dry fruits, and garlic. If the bathroom smell is pretty rancid, try reducing the amount of sulfur-containing foods you eat (but don’t cut them out entirely; sulfur is essential to the body).

You’re eating high-fat foods

Foods that are high in fat can also cause smelly and even "oily" poop. “The fat left over that could not be broken down won't be absorbed by the colon, and thus it passes through in an undigested form,” Dr. Sonpal says.

This results in a smelly diarrhea-like stool referred to as steatorrhea. Again, no harm, but if you’re eating tons of fast food that is high in oily fats and have this problem frequently, you may want to dial it back for health reasons, too.

Plus, if you aren't on a high-fat diet like the keto diet but still notice steatorrhea, check with your doctor, as this could be an indicator that your body is having an immune reaction to gluten.

You have a food intolerance

Besides gluten, dairy could be an issue for you. “When your system doesn't tolerate lactose, and you consume milk or milk-based ice cream, you are risking a very stinky run for the bathroom brought about by malabsorption,” he explains. So if scary post-dairy poops sound familiar to you, get checked by a doctor to see if you’re lactose-intolerant. Also, try cutting out the lactose for a while and seeing if it fixes the stool’s odor.

You’re boozing

Beer, wine, whiskey—of all things, alcohol could lead to smelly poop later on. “High levels of alcohol in the blood can affect organs in the body, such as your stomach and the intestines,” Dr. Sonpal says. High concentrations of alcohol can affect the flora in your intestines, so it doesn’t do its job as well as usual. The result: foul-smelling gas and poop. To mitigate it a bit, try drinking extra water when you have alcohol. (Good for you for a number of reasons.)

You’re on certain medications

“Medications like antibiotics or hormones can mess with gut bacteria, speeding up or slowing down the way poop moves through your intestines,” Dr. Sonpal says. Or they can cause malabsorption of certain nutrients, thereby causing smelly diarrhea. Either way check with your doc if your poop changed when your medications did.

Isadora Baum is a freelance writer, certified health coach, and author of 5-Minute Energy. She can't resist a good sample, a margarita, a new HIIT class, or an easy laugh. Learn more about her on her website: isadorabaum.com. 

It’s pretty much a given that your poop is never going to come out smelling like roses. But, while it doesn't exactly smell great on the reg, a really bad odor can be a sign that something is off with your health.

First, it’s important to go over some Number-Two basics. Poop (a.k.a. stool or feces) is “a bodily waste that is passed through the gastrointestinal tract and is made up of water, dead microorganisms, undigestible food matter, and some fats and cholesterol, in addition to several other minor components,” says gastroenterologist Marvin Singh, MD.

There are actually a few different reasons why it usually smells. “This odor is from the undigested food, as well the gas produced by the bacteria in the gut,” says Seyedehsan Navabi, MD, assistant professor of clinical medicine at the Rutgers New Jersey Medical School. The most common odor-causing gases, in case you want specifics, are hydrogen sulfide, which has a lot of smelly sulfur, methyl sulfides, and benzopyrrole volatiles, he says.

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But the amount of gas in your poop—and how stinky it is—really depends on what you eat and how healthy you are, Dr. Navabi says. Example: You might have smellier-than-usual BMs after you eat a steak, because meat protein is rich in the amino acid methionine, which can create stinky sulfur-containing compounds. Cue you staring at your toilet, wondering what’s going on.

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  11 Reasons Why You’re Pooping Way More Than Usual

If you have a few random stinky poops here and there, it’s likely no big deal. But if you notice that you’re regularly being blown away by just how much smell you’re producing, it could be a sign that something is off. Here are the biggest reasons your poop is so smelly, plus when it’s time to see a doctor about it.

What causes smelly poop?

There are actually a lot of potential things you can point a finger at, with some being more of a big deal for your health than others.

1. You’re taking antibiotics.

Your gut has what’s known as a bacterial flora, which is a collection of microorganisms that help break down your food. But, when you take antibiotics, it can tweak your bacterial flora “which leads to different byproduct,” says Aniqa Kohen, MD, a gastroenterologist at UBMD Physician’s Group. That change in bacteria can cause a change in smell, too.

2. You have an infection.

An infection can also mess with the bacteria in your gut. “Different bacterial, viral or parasitic infections can affect the digestive tract,” Dr. Navabi says. While they might cause diarrhea, they can also change the gas in your poop and create a smelly odor, he says.

3. You have a food intolerance or allergy.

When you have a food intolerance or allergy, your body can’t properly process a particular ingredient, Dr. Singh says. The combination of gas produced by bacteria that try to break it down and undigested food can lead to a stinky smell. It can also cause you to have stomach cramps and sometimes bleeding.

4. You have Celiac disease.

Having Celiac disease means that your body has an immune reaction to eating gluten, a protein found in wheat, and attacks the lining of the small intestine, Dr. Navabi explains. That damage to the lining of the gut can make it difficult to absorb nutrients and, as a result, you end up with symptoms like diarrhea or constipation, bloating, gas, stomach pain, and greasy, smelly poop.

5. You have inflammatory bowel disease.

Inflammatory bowel disease (IBD) is an umbrella term used to describe several autoimmune conditions like Crohn’s disease and ulcerative colitis. Inflammation of the colon with ulcerative colitis can alter bacteria in the gut and cause bleeding—and both can lead to strong-smelling Number Two, Dr. Navabi says. Crohn’s disease can cause similar issues, along with difficulty absorbing nutrients, and that can also lead to stinky poop, he says. IBD as a whole can cause uncomfortable symptoms like diarrhea, stomach pain, nausea, and vomiting.

6. Your body isn’t absorbing your food properly.

There are a lot of things that can lead to your body not absorbing nutrients properly (aka malabsorption), Dr. Kohen says—an infection, gluten allergy, gut inflammation, and several syndromes. “Any time chronic inflammation occurs in the gut, it can alter the balance of the bacteria,” Dr. Navabi says. And that can add more gas to your poop. Cue the stink.

When should I see a doctor for super smelly poop?

Any time things seem off down there and they don’t go away after a few days or seem to be getting worse, it’s a good idea to call your doctor. But Dr. Kohen says you should call sooner rather than later if you have any of the following along with your persistently smelly poop:

• Nausea
• Vomiting
• Weight loss
• Blood in your poop
• A family history of cancer or IBD
• Fever
• Chills
• Joint swelling
• Ulcers in your mouth
• Pain around your eyes
• Waking up at night to poop
• You can’t get relief from over-the-counter medications

How can I avoid smelly poops?

If your smelly poop doesn’t seem to be linked to something serious, like intestinal bleeding, and you’re not having other severe symptoms, there are a few things you can do.

• Take a closer look at your diet. If you’ve been eating a lot of garlic or onions lately, that could definitely be the culprit. But sometimes it can be a little harder to know what’s leading to that smell. “Often keeping a food diary might help you figure out what foods upset your gastrointestinal tract,” Dr. Singh says, adding that you should keep an especially close eye on gluten and dairy.
• Try eliminating some foods. You can try weeding out certain foods, like meat, eggs, broccoli, cauliflower, and asparagus, Dr. Kohen says. These are notorious for causing stinky poops.
• Consider using a probiotic. Probiotics can help restore the balance of healthy bacteria in your gut and “can help settle some GI symptoms if they are minor,” Dr. Singh says.
• Drink more water. Sometimes, hydrating more can help flush out the stinky smell. “It is important to have adequate hydration for the health of the gut,” Dr. Navabi says.

The bottom line: Smelly poop is mostly harmless, Dr. Navabi says, especially if you don’t have any other symptoms. But, if it doesn't go away, and you've noticed some other symptoms along with your stinky poo, call your doctor about next steps.

Korin Miller is a freelance writer specializing in general wellness, sexual health and relationships, and lifestyle trends, with work appearing in Men’s Health, Women’s Health, Self, Glamour, and more. She has a master’s degree from American University, lives by the beach, and hopes to own a teacup pig and taco truck one day.