18 Possible Reasons Your Breath Smells Bad

Having bad breath is kind of like getting toilet paper stuck to the bottom of your foot: usually harmless, but so awkward that nobody will tell you about it. According to the American Dental Association (ADA), at the microbial level, bad breath happens when the naturally occurring bacteria in our mouths break down the food particles that are lingering in between our teeth, along our gum lines, and, especially, on our tongue. This process releases a bunch of stinky compounds and gives rise to the dreaded bad breath—or, as it's more formally called, halitosis.

The good news: It's is usually temporary. The bad news? It's often caused by a less-than-stellar brushing and flossing routine—as well as a bunch of habits. Here are 18 possible reasons your breath smells bad.

You Just Woke Up

Obviously, right? Yep, morning breath is pretty much a given, but here's why it happens: According to a June 2012 study published in the International Journal of Oral Science, while you're sleeping peacefully, the bacteria in your mouth are anything but.

The bugs take advantage of the fact that your production of saliva slows way down during sleep—and since your saliva helps "clean" your mouth, your breath might have a bad odor until you brush your teeth the following day. Morning breath is totally normal and will disappear as soon as oral hygiene measures are taken.

You're Breathing Through Your Mouth

Mouth-breathing may make your saliva evaporate, which can dry out your mouth and reduce your mouth's ability to rinse away food particles. Some people breathe through their mouths while they sleep, but many people often do it during exercise as well, said Hadie Rifai, a dentist at the Cleveland Clinic.

In fact, dental hygiene in athletes is currently being studied: One January 2015 study published in the British Journal of Sports Medicine found that the more time people spent in training, the more likely they were to have cavities. The scientists also speculated that the reduced saliva flow during exercise may play a role.) That's not a reason to stop exercising, of course. Just make sure you stay hydrated during a workout and replenish your fluids afterwards, said Dr. Rifai.

You Ate Some Smelly Food

Garlic and onions are two famous offenders, but other culprits include spices, cabbage, Brussels sprouts, cauliflower, and radishes. Even though the pungent scent of those foods might fade away after an hour or two, it can still come back up again—in one big garlicky burp.

According to the ADA, bad breath from food can occasionally stem from the GI tract, not just your mouth. When you digest food, the chemicals are eventually absorbed into your bloodstream and enter your lungs, where you can expel them later," said John Grbic, a dentist at Columbia Doctors in New York City.

You Haven't Eaten All Day

Skipping meals is a surefire way to have bad breath. That's because when we don't eat, we don't produce as much saliva.

Why's that important? Because saliva doesn't just clean up food particles, it also breaks down that food to help it slide down our throats more easily, said Dr. Grbic. (Oh, and one more thing: Skipping meals isn't a very good way to lose weight, either.)

You Smoke

Add halitosis to the list of health conditions that cigarettes can cause, according to the ADA.

A 2015 study published in the journal Acta Stomatologica Croatica found that long-term smoking reduces the secretion of saliva and changes its quality. Saliva plays a significant role in maintaining oral health and oral hygiene by washing away food and bacteria. In addition, enzymes and antibodies from saliva can destroy bacteria in the mouth and on the the teeth that can lead to bad breath and tooth decay.

You're Taking a Medication

Many medications can cause bad breath. A 2020 study in Oral Health and Preventive Dentistry analyzed published studies to identify medications that can cause extra-oral halitosis—a type of halitosis caused by systemic conditions, bloodborne diseases, or pharmaceutical therapy. The authors categorized medications that can cause extra-oral halitosis into 10 groups: Acid reducers; aminothiols; anticholinergics; antidepressants; antifungals; antihistamines and steroids; antispasmodics; chemotherapeutic agents; dietary supplements; and organosulfur substances.

If you are taking any of these medications, you may be at higher risk of developing bad breath.

You Have Post-nasal Drip

According to the 2012 study published in the International Journal of Oral Science, mucus in your nose helps filter all the foreign particles that you breathe in from the environment—which is a good thing.

But what happens when that mucus starts building up in the back of your throat because you have terrible pollen allergies or a nasty cold? Those foreign particles eventually travel into your mouth, settle on the surface of your tongue, and in turn trigger bad breath, according to the International Journal of Oral Science study. As if a sore throat wasn't bad enough.

You're on a Low-carb Diet

People who slash their carbohydrate intake have been known to report increased levels of halitosis. According to a September 2012 study published in Obesity journal, when subjects on a very low-carb diet were compared to those on a low-fat diet, researchers found that more people in the former group reported having bad breath than the latter.

Though, it should also be noted, the low-fat dieters also confessed to more burping and farting.

You Have a Cavity

Your dentist has already warned you that a buildup of plaque can erode your teeth, leaving you with cavities. Technically, according to the National Library of Medicine, cavities arise from tooth decay, or damage to a tooth's surface, which happens when bacteria in your mouth make acids that attack the enamel.

And while poor oral hygiene certainly contributes to bad breath, those "holes" may also trigger halitosis indirectly, too, according to the the International Journal of Oral Science study.

"Food can get caught in the cavities," said Dr. Grbic, and since cavities can be hard to clean, the remnants of your last meal can linger there for longer-than-usual periods of time, which can then lead to more bad breath. (For the record, yes, you'll need a filling.)

You Wear a Dental Appliance

We're not just talking about braces—orthodontic appliances like dentures and fixed bridges can be difficult to maintain too. But it's important that you clean them every day, said Dr. Grbic, as they're also prime magnets for food particles, which can become lodged in the material.

Research published in the journal Schweizer Monatsschrift fur Zahnmedizin in 2013 showed that dental appliances are linked with higher amounts of plaque accumulation—which is why a good cleaning regimen is so important.

You Drink a Lot of Alcohol

Alcohol lingers on your breath long past last call. In fact, one 2017 study published in British Dental Journal noted a significant association between increased drinking frequency and halitosis.

Increased levels of sulphur compounds in daily drinkers bears some of the responsibility, as well as the short term effect of the smell of the alcohol itself, increased dry mouth, worse oral hygiene and increased periodontal disease.

You Get Heartburn

The overwhelming majority of halitosis cases are caused by the bacteria in a person's mouth—but researchers also suspect that in a minority of people, bad breath is triggered by a GI disorder like gastroesophageal reflux disease (GERD), in which the contents of a person's stomach leak back up into the esophagus, according to the National Library of Medicine.

One 2017 study published in BMC Gastroenterology noted that approximately 60% of patients presenting to dentists with erosive tooth wear had significant GERD. Among the factors leading to progressive tooth decay in the GERD patients were increased exposure of the teeth to refluxed acid, and other substances such as bile, a digestive aid stored in the liver.

You Have Strep Throat

Strep is a bacterial infection, not a viral one, according to the National Library of Medicine. Those invading bugs can cause your bad breath to smell bad, said Dr. Grbic.

Not only that, but other kinds of sinus infections can turn into bacterial ones that produce a smelly, pus-like type of mucus. In addition, some of these infections are also associated with specific types of bacteria that are known to produce a particularly bad odor in a person's mouth.

Your Oral Bacteria Differs From Your Minty-fresh Friend's

Here's the thing: Your partner might wake up in the morning smelling like half-a-bottle of Listerine, while you might eat an onion ring and have to cover your mouth for the next 30 minutes. And in some cases, that might not have anything to do with how often either of you brush your teeth.

Everyone has their own saliva composition and different kinds and levels of oral bacteria, all of which affect how your breath will smell in certain situations, said Dr. Rifai.

Your Blood Sugar Levels Are Super High

You probably don't need to worry about this one unless you have type 1 diabetes. It's pretty rare. According to the International Journal of Oral Science study, if your breath develops a sweet, almost sugary scent to it, that's a sign that you might be experiencing diabetic ketoacidosis, a life-threatening condition for people with diabetes (usually type 1) that could cause a heart attack or kidney failure.

Other symptoms include frequent urination, nausea, and muscle stiffness. According to Dr. Grbic, dentists almost always see this in patients with undiagnosed diabetes. It's often a sign that their blood sugar levels are dangerously high and they need medical help right away, said Dr. Grbic.

You Have Sjogren's Syndrome

Sjogren's syndrome (SS), according to the National Library of Medicine, is a disorder of the immune system that tends to show up in middle-aged women and those with other autoimmune conditions like rheumatoid arthritis and lupus.

That said, even young, otherwise healthy people can develop SS—Venus Williams was diagnosed in 2011. People with SS often have a very dry mouth , which—you guessed it—increases their risk of halitosis.

You Have Gum Disease

Bad breath is a warning sign of periodontal diseases, according to the Centers for Disease Control and Prevention (CDC). Periodontal disease is the result of infections and inflammation of the gums and bone that surround and support the teeth. Called gingivitis in its early stage, the gums become swollen and red, and they may bleed. Periodontitis is its more serious form. In this stage, the gums pull away from the tooth, bone can be lost, and the teeth may loosen or even fall out.

A rare infectious disease of the gum tissue called acute necrotizing ulcerative gingivitis (ANUG) is diagnosed by, among other symptoms, a strong and fetid odor, according to the National Library of Medicine. This disease affects less than 1% of the population but is a painful and destructive ulceration and inflammation of the gum tissue caused by opportunistic bacterial infection. ANUG is more common in young, particularly severely malnourished children and young adults with human immunodeficiency virus (HIV) infection.

You Just Think You Have Bad Breath

Up to 1% of people may have a disorder called halitophobia, according to the International Journal of Oral Science study. This is a false belief that they have bad breath. It's a serious condition, and one that be extremely debilitating. To be clear: We're not talking about just a lingering suspicion of bad breath—we mean a persistent fear of it. People with halitophobia become absolutely convinced that their halitosis is driving other people away, even after a dentist has confirmed that they don't have the condition.

Unfortunately, this phobia isn't well-studied, but if you suspect that you might have it, it's important to seek psychological help from a counselor or a specialist.