Why do my bowel movements smell metallic

Poop that smells bad is totally normal, but there are a few specific smells that can tip you off to gut problems.

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Look, there's a reason why bathrooms are equipped with a fan: Yeah, it's to get rid of moisture from your shower, but it also zips odors outta there. Because, people, your poop smells.

Granted, you probably already know that. But did you know the fragrance of your feces (sorry, couldn't resist), can clue you into what's going on inside your body?

Wait, Why Does Poop Smell?

First, though, let's chat about ​why​ your poop smells. You might notice that your BMs, in general, tend to have a similar scent.

"The routine odor of stool is based on your gut microbiota. Namely, the type of bacteria you have and how this bacteria ferments the food in your diet," Michael D. Brown, MD, gastroenterologist and professor of medicine at Rush University Medical Center in Chicago, tells LIVESTRONG.com.

(This microbiota was "given to you by your mother," and is difficult to change, adds Dr. Brown. If you are taking antibiotics or probiotics, once you stop taking them, your gut microbiota will revert back to your body's normal.)

Still, it's the food you eat that can make a specific poop more putrid or pleasant:

• ​Carbohydrates​ are highly fermentable, and they influence this smell, says Dr. Brown.
• ​Garlic and onions​ are top offenders that make things more odorous, as they contain sulfates, which break down into smelly substances. (Hence, why your poop smells so bad or smells like sulfur.)
• ​Legumes and beans​ contain an enzyme that inhibits their digestion, which will give you more gas (which, you know, smells).

That rotten-egg smell? Typical. Other sulfate-containing culprits, in addition to that garlicky spinach or fajitas topped with sauteed onions, are ​high-fat foods, dairy, meat and alcohol​, says Niket Sonpal, MD, an internist and gastroenterologist in New York City.

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What Different Poop Smells Might Mean

In other words, it's totally normal to have smelly poop.

"It's not necessarily unhealthy for your poop to smell. Some people have smellier stool than others, and most people occasionally experience rancid-smelling poops," Dr. Sonpal says.

That said, it's a good idea to pay attention to your personal perfume (whether sweet or skunk-like) because there are a few signs that something more may be going on.

If you have blood in your stool, your poop will have a "unique and unmistakable smell," says Dr. Brown. GI doctors, he says, can readily identify this when they walk down the hall of a hospital, but for the untrained nose (that's you), rather than sniffing out blood, pay attention to the way it looks.

Black, tarry stools are a red flag, as this indicates the presence of blood, which indicates bleeding in the upper part of the GI tract (esophagus, stomach or part of the small intestine), according to the U.S. National Library of Medicine. This symptom can indicate a peptic ulcer or even esophageal or stomach cancer. Always call your doctor if you have black, tarry stools.

"It's not necessarily unhealthy for your poop to smell. Some people have smellier stool than others, and most people occasionally experience rancid-smelling poops."

2. Your Poop Smells Like Vomit or Sewer Gas (aka Really Bad)

Another reason to get on the phone with your doc? If the smell is "genuinely and severely unbearable," says Dr. Sonpal.

If your stool is also waxy or tacky in texture, or if there's a sudden, drastic change in the frequency, consistency or your comfort in going to the bathroom, call up your doctor. These may be signs of infection or a digestive condition, he says.

One example of an infection that contributes to an unpleasant BM bouquet: Giardiasis, an intestinal parasite. You can get this when eating contaminated food or drinking contaminated water (like from a stream when camping). Along with smelling bad, you'll also get explosive, watery diarrhea, notes Johns Hopkins Medicine. The tricky part is that symptoms don't usually start until one or two weeks after you're infected, so it may be tough to pin down exactly what happened.

Digestive conditions that can contribute to foul-smelling stool include celiac disease, Crohn's disease, chronic pancreatitis and diseases that cause malabsorption, like cystic fibrosis and pancreatic infection, according to Mount Sinai.

Malabsorption could mean that you're not properly absorbing fats (called steatorrhea), which results in a "rotten food smell," says Dr. Brown. Also look for lighter-color stools (like clay or white), which may clue you into something going on with your pancreas.

3. Your Poop Smells Sweet

An infection that can lead to a very unpleasant, sweet-smelling stool is ​C. diff,​ which can happen when you're taking antibiotics and also includes symptoms such as diarrhea, fever, loss of appetite and stomach pain, according to the Centers for Disease Control and Prevention. If you have any of these symptoms, let your doctor know.

Bottom line: Stinky poop is normal. If it's extra smelly, it's usually in relation to something you ate, but it may also be indicative of a gastrointestinal disorder or infection. Talk to your doctor if you're concerned, your bowel habits have changed or you notice signs of blood in your stool.