Eating garlic and a lax teeth-brushing routine aren't the only answers to the question, "Why does my breath smell?"

Maria Masters

Updated on August 21, 2023

 Medically reviewed by 

Edmund Khoo, DDS

THARAKORN / GETTY IMAGES

Halitosis, or bad breath, happens when bacteria eat leftover food in your mouth, producing smelly compounds.¹ Bad breath can result from eating habits, smoking, or health conditions like heartburn and high blood sugar. Read on for more on these and other possible reasons your breath smells bad.

1. Dental Appliances

Orthodontic appliances like dentures and fixed bridges can be difficult to maintain. It's important that you clean them daily, John Grbic, DMD, a dentist at Columbia Doctors in New York City, told Health. They're prime magnets for food particles, which can become lodged in the material and could lead to bad breath.

 What Is Tongue Scraping and Should You Do It?

2. Eating and Drinking Patterns

What you eat or drink and how you do so can be the cause for bad breath.

Drinking Alcohol

Alcohol can linger on your breath for a while. One study noted a significant association between increased drinking frequency and halitosis.²

Factors responsible for why a person's breath may smell bad include:²

• Increased dry mouth

• Increased levels of sulfur compounds in daily drinkers

• Increased periodontal disease

• Short-term effect of the smell of the alcohol itself

• Worse oral hygiene

Eating Smelly Food

Condiments, garlic, onions, pickles, radishes, and spices are some foods that make your breath smell bad. 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.³

Bad breath from food can occasionally stem from the GI tract, not just your mouth.³ "When you digest food, the chemicals are eventually absorbed into your bloodstream and enter your lungs, where you can expel them later," said Dr. Grbic.

Following a Ketogenic Diet

The ketogenic (keto) diet is a popular low-carbohydrate, high-fat diet originally developed to treat epilepsy. Eating a low amount of carbs puts your body into a metabolic state called ketosis, which allows you to burn fat, resulting in rapid weight loss.⁴

When your body is in a ketogenic state, you may notice what is called keto breath. This happens because your liver enzymes are converting acetone to isopropanol.⁴ The odors released during this conversion can make their way to your breath.

Keto breath may smell like acetone—the same stuff used in nail polish remover. However, it can also have a fruity smell.⁵

Not Eating All Day

Skipping meals is a surefire way to have bad breath. That's because you don't produce as much saliva when you don't eat. Food increases the amount of saliva you have in your mouth.⁶

3. Halitophobia

Up to 1% of people may have a disorder called halitophobia.³ This is a false belief that they have bad breath. It's a serious condition and one that can be extremely debilitating.

This isn't just a lingering suspicion of bad breath—it's a persistent fear. People with halitophobia become convinced that their halitosis drives others away, even after a dentist has confirmed that they don't have the condition or with treatment.⁷

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

4. Health Conditions

Sometimes halitosis can be a symptom of a health condition like heartburn, high blood pressure, or Sjogren's syndrome.

Heartburn

Most halitosis cases are caused by the bacteria in a person's mouth. Researchers also suspect that in a minority of people, bad breath is triggered by a GI disorder like gastroesophageal reflux disease (GERD). GERD is a condition in which the contents of a person's stomach leak back into the esophagus.⁸

One study noted that approximately 60% of patients presenting to dentists with erosive tooth wear had significant GERD. Increased exposure of the teeth to refluxed acid and other substances such as bile, a digestive aid stored in the liver, was among the factors leading to progressive tooth decay in patients with GERD.⁹

High Blood Sugar

If your breath develops a sweet, almost sugary scent, that's a sign that you might be experiencing diabetic ketoacidosis. Diabetic ketoacidosis is a life-threatening condition for people with diabetes (usually type 1) that could cause a heart attack or kidney failure.¹⁰

Other symptoms include frequent urination, nausea, and muscle stiffness.¹⁰ 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.

Sjogren's Syndrome

Sjogren's syndrome (SS) is a disorder of the immune system. SS tends to appear in middle-aged women and those with other autoimmune conditions like rheumatoid arthritis and lupus.¹¹

Even young, otherwise healthy people can develop SS. Halitosis has been associated with an SS diagnosis due to individuals having a dry mouth.¹²

5. Hygiene Problems

Good oral health can help prevent the experience of bad breath.¹ However, not flossing or brushing your teeth regularly can result in problems like cavities and gum disease associated with halitosis.

Cavities

A buildup of plaque can erode your teeth, leaving you with cavities. Technically, cavities arise from tooth decay or tooth surface damage. This happens when bacteria in your mouth make acids that attack the enamel.¹³

While poor oral hygiene certainly contributes to bad breath, those "holes" may also trigger halitosis indirectly.¹⁴

"Food can get caught in the cavities," said Dr. Grbic. Since cavities can be hard to clean, the remnants of your last meal can linger there for longer-than-usual periods, leading to more bad breath.¹⁴

Gum Disease

Bad breath is a warning sign of periodontal disease, also called gum disease. Periodontal disease results from infections and inflammation of the gums and bone surrounding and supporting the teeth.¹⁵

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. ANUG affects less than 1% of the population but is a painful and destructive ulceration and inflammation of the gum tissue due to bacterial infection.¹⁶

6. Illness-Related Factors

Some aspects of being sick, like if you have postnasal drip or strep throat, can result in halitosis.

Postnasal Drip

Mucus can build up in the back of your throat due to terrible pollen allergies or a nasty cold. The foreign particles in the postnasal drip eventually travel into your mouth, settle on the surface of your tongue, and trigger bad breath.¹⁷

Strep Throat

Strep is a bacterial infection, not a viral one.¹⁸ Those invading bacteria can cause your 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.¹⁹

In addition, some of these infections are also associated with specific types of bacteria that are known to produce a terrible odor in a person's mouth.²⁰

 What Is Thrush?

7. Medications

Many medications can cause bad breath. One study analyzed published studies to identify drugs that can cause extra-oral halitosis, caused by systemic conditions, bloodborne diseases, or pharmaceutical therapy.²¹

The authors categorized medications that can cause extra-oral halitosis into 10 groups:²¹

• Acid reducers

• Aminothiols

• Anticholinergics

• Antidepressants

• Antifungals

• Antihistamines and steroids

• Antispasmodics

• Chemotherapeutic agents

• Dietary supplements

• Organosulfur substances

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

8. Morning Breath

Morning breath is normal bad breath that you notice upon waking. It happens because, while you're sleeping peacefully, the bacteria in your mouth are not.²²

The germs take advantage of the fact that your saliva production slows down during sleep. Since your saliva helps "clean" your mouth, your breath might have a bad odor until you brush your teeth the following day.²²

9. Mouth Breathing

Mouth breathing has been associated with breath that smells bad.²³ Some people breathe through their mouths while they sleep, but many people often do it during exercise as well, said Hadie Rifai, DDS, a dentist at the Cleveland Clinic.

10. Oral Bacteria Differences

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.²⁴

For example, someone you know 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.

11. Smoking

Smoking can contribute to halitosis. One study found that long-term smoking reduces the secretion of saliva and changes its quality. Saliva plays a significant role in maintaining oral health and hygiene by washing away food and bacteria.²⁵

In addition, enzymes and antibodies from saliva can destroy bacteria in the mouth and on the teeth, which can lead to bad breath and tooth decay.²⁵

How To Prevent Bad Breath

There are ways to keep bad breath at bay, including:²⁶¹

• Avoid alcoholic beverages, bad breath-causing foods, and tobacco products

• Chewing sugar-free gum

• Cleaning dentures, retainers, and mouthguard regularly, if you wear them

• Eating more fruits and vegetables and less meat

• Maintaining good oral hygiene, like brushing your teeth twice daily and flossing once daily

• Making regular dental visits

• Using over-the-counter (OTC) mouthwashes

 How Much Toothpaste Should You Use?

A Quick Review

Your breath may smell bad for many reasons, including if you've eaten certain foods you eat, you smoke, or you are sick and have postnasal drip. Fortunately, practicing good oral hygiene by brushing and flossing regularly and limiting foods and drinks that lead to bad breath can prevent halitosis.