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7 Causes of Bad Breath, Plus When to See a Doctor

Emily Turner

Shot of a beautiful young woman checking her breath at home

It’s normal to have bad breath from time to time, especially after eating potent foods like garlic and onions, but persistent sour, rotten, or sulfur-like breath may be a deeper issue. If tossing in a piece of gum doesn’t freshen up the problem, bad breath from your stomach, teeth, or gums may be to blame.

“Bad breath, also known as halitosis, is when your breath is noticeably offensive to yourself and/or others,” says Matthew Reck, DDS, a board-certified dentist and owner of Chikaming Dental Center in Sawyer, Michigan.

As the name suggests, bad breath creates a smelly odor often accompanied by a foul taste in your mouth, says Laura Purdy, MD, a board-certified family-medicine physician. Bad breath can be due to a temporary or chronic condition, but identifying the culprit can help stop and prevent the issue once and for all, she adds.

Curious what you may be dealing with? Ahead, seven causes of bad breath and how to stop the smell.

Causes of Bad Breath

Bad breath isn’t always a major sign of concern, considering bad breath reasons can range from the foods you eat to the type of oral hygiene you practice — both of which can be remedied quickly. Other times, the cause of your bad breath may be more serious, including gum disease and respiratory infection. Below, experts weigh in on common bad breath causes and how to spot the signs.

Poor Oral Hygiene

Poor oral hygiene is a primary cause of bad breath, says Dr. Reck. “If you don’t remove the food and plaque (sticky film of bacteria that forms on your teeth) from your mouth, it will produce bacterial growth and odor,” he explains. Dirty dental appliances like retainers, dentures, and bite splints may also be the culprit since they can easily grow bacteria, fungus, and yeast if not properly cleaned, he adds.

Food naturally gets stuck in your teeth, so it’s important to remove trapped leftovers before they start to decay, says Dr. Purdy. The solution? Brush, floss, and schedule routine dental cleanings to minimize harmful bacteria in your mouth from multiplying, Dr. Reck explains. Scraping your tongue and using an antiseptic mouthwash can also reduce the buildup of bacteria in the mouth to keep your breath fresh, he adds.

Dry Mouth

Dry mouth, also known as xerostomia, happens when there is a decrease in saliva production and is often caused by certain medicines, smoking, alcohol, stress, or always breathing through your mouth instead of the nose, says Dr. Reck. “Saliva helps wash your mouth from odor-causing bacteria, and when there’s a decrease in saliva production, the mouth can’t cleanse itself,” he explains.

Drinking plenty of water is key for preventing dry mouth, but chewing sugar-free gum can also increase your saliva production, Dr. Reck says. You can also talk to your doctor about artificial saliva substitutes, like Biotene, to soothe symptoms, he adds.

Gum Disease

Gum disease (AKA periodontal disease) is an infection of the tissues that hold your teeth in place and is typically caused by the buildup of plaque due to poor brushing and flossing habits, Dr. Reck says. These small openings between the teeth collect food, plaque, and bacteria, and present red, swollen, bleeding gums, and persistent bad breath, Dr. Purdy adds.

To prevent gum disease, brush your teeth twice daily, floss, scrape your tongue, and schedule professional dental cleanings at least twice a year, Dr. Reck says. Antiseptic mouthwashes containing chlorhexidine or other antibacterial agents can also kill bacteria and freshen your breath, he explains. You should also quit or avoid smoking as it can cause and/or worsen gum disease, he adds.

Tooth Decay

Like gum disease, tooth decay is caused by the buildup of plaque and bacteria which feeds off leftover food particles in your mouth and causes a sulfur-like odor, Dr. Reck says. The small crevices in your teeth also create perfect pockets for food and plaque to harbor in, so it’s especially important to thoroughly brush your teeth twice a day and maintain twice yearly dental cleanings, he adds. If you suspect you have tooth decay, also known as a cavity, visit your dentist asap.

Respiratory Infections

Believe it or not, respiratory infections, sinus infections, and postnasal drip can all lead to bad breath, says Dr. Reck. “When you have a cold or postnasal drip, you get what we refer to as phlegm or mucus, and the bacteria in your mouth and on your tongue feeds off of it and multiplies, causing a foul smell,” he explains. Regular oral hygiene can minimize the breeding grounds for bacteria but talk to your doctor if symptoms worsen or persist.

Gastrointestinal Issues

Gastrointestinal issues such as heartburn or reflux can cause smelly breath, especially after eating, Dr. Reck says. Acid reflux is the backward flow of undigested food and stomach acids into your esophagus, which is particularly potent and can cause a sour odor, he explains. Fiber-rich foods can help promote digestion but talk to a physician about any underlying medical issues, he adds.


Foods like garlic, onion, spices, and coffee are known to cause bad breath, and if these food particles remain in and around your teeth, it can worsen the issue, says Dr. Purdy. To squash the stench, rinse your mouth with water after you eat, toss in a piece of sugar-free gum, or regularly brush your teeth after meals, Dr. Reck adds.

When to See a Doctor For Bad Breath

“Fortunately, the most common causes of bad breath are the easiest to address,” says Dr. Reck. “Increase your daily oral health regime, so if you’re brushing twice a day, make it three or four times a day, floss twice a day instead of once, and add a mouthwash that’s antibacterial to help reduce or eliminate the odor,” he explains.

If there is no significant change in or improvement in your bad breath after one to two weeks, schedule a visit with your dentist, says Dr. Reck. From there, they will determine the cause by checking for oral infections and disease.

In terms of bad breath treatment, it depends on your situation, says Dr. Reck. “If it’s due to poor oral hygiene, get a professional dental cleaning and increase at-home care,” he explains. “If it’s due to gastrointestinal issues or respiratory infections, see your primary care physician for over-the-counter suggestions or prescription options.”

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