What causes bad breath and how can it be prevented?

Bad oral hygiene is the most common reason for having bad breath, after all, not brushing your teeth enough or properly means that food particles remain in your mouth, which promotes bacterial growth that leads to bad breath.

Solve it:

“In order to maintain healthy teeth and gums, it’s vital to brush your teeth twice a day with a fluoride toothpaste. Your toothbrush should clean one tooth at a time for around three to five seconds,” explains leading cosmetic dentist Dr Sam Jethwa. “You should also be flossing at least once a day, if not twice. If you are opting for only once a day, then look to do this in the evening before bed, as this will reduce the build-up of bacteria in the mouth that occurs throughout the night, which can lead to bad breath.”

Reason 2: You suffer with dry mouth

Xerostomia is the official medical name for having a dry mouth, which can be caused by a multitude of things, but can also cause bad breath.

“A dry mouth can cause bad breath because saliva protects our mouth, so when there is less of it, bacteria can breed faster,” explains Dr Jethwa. “Not only this, but food debris is less likely to be washed away.”

Solve it:

Make sure you’re staying as hydrated as possible and drinking plenty of water. Chewing sugar-free gum can also help stimulate saliva production. Alcohol and caffeine are known to worsen dry mouth too, so avoid if this could be exacerbating the problem.

Reason 3: You’re eating problem foods

We’ve all been there – you’ve enjoyed a garlic-laden dish and suddenly all you can smell, and taste, is the lingering stench of garlic. Strong-smelling foods like garlic and onions can unfortunately cause bad breath because they release sulphur compounds that linger in the mouth and the digestive system. But other things can be to blame including following certain diets, too much dairy and even acidic foods.

“Low-carb diets like keto can cause bad smelling breath,” explains registered nutritionist Zara Hiridjee. “Your body shifts to burning fat for fuel, which produces ketones. Ketones are released through your breath, and they often carry a noticeable ‘fruity’ or slightly metallic odour, which people refer to as keto breath. Fasting can also lead to bad breath as saliva production drops since there’s no food in the mouth stimulating it.”

Dairy foods like milk and cheese can also be to blame, says Dr Jethwa. “These foods contain amino acids, which will increase the bacteria on the tongue. It is also important to note that if you have a high-protein diet, this can result in excess amino acids, therefore leading to bad breath.”

Any foods that are acidic can also create bad breath, as it promotes a breeding ground for bacteria. Think foods like tomato sauce, barbecue sauce, citrus fruits and fish.

Solve it:

Reason 4: You have gum disease

Persistent bad breath, medically known as periodontitis, can be a sign of gum disease.

“Gingivitis is incredibly common, and is the term used for gum disease when it is in its early stages. If not treated, gingivitis can eventually lead to periodontitis, which can cause teeth to become loose and fall out,” explains Dr Jethwa. “The most common cause of gingivitis is poor oral hygiene, which will cause a buildup of bacteria and plaque on the gums. Plaque is the sticky film which covers the teeth, plaque forming is normal but if it is not removed then it can cause oral health issues.

Solve it:

As well as keeping up good oral hygiene, focusing on brushing your gums, too, you should be regularly (twice annually at least) visiting a dentist for a professional clean, and to assess the severity of the gum disease.

Reason 5: You smoke or vape

Smoking is already one of the leading causes of many diseases, but cigarettes and other tobacco products can also leave a nasty stench thanks to the chemicals left behind in your mouth.

Smoking increases your risk of gum disease, as Dr Jethwa points out: “Smoking may also cause the gums to change colour and appear grey and increase the production of plaque due to a reduction of saliva in the mouth which will cause bad breath.”

Vaping isn’t much better either as, when people inhale during vaping, the sticky, sugary content of vaping liquid sticks to the teeth causing damage to the tooth enamel.

“It also changes the microbiome of the mouth, making it more hospitable to decay-causing bacteria which will also cause bad breath,” warns Dr Jethwa. “As well as this, vaping appears to encourage decay in areas where it usually doesn't occur, such as the bottom edges of front teeth and can decrease saliva production.”

Solve it:

Yet another reason to quit. Find support at your local NHS stop smoking service.

Reason 6: You’re ill, or have a certain medical condition

Certain medical conditions including diabetes, gastroesophageal reflux disease (GERD), respiratory infections, or liver/kidney problems, can all contribute to bad breath.

“Illness, particularly infections, often changes the way that someone smells and affects their breath,” explains GP and allergy specialist, Dr Helen Evans-Howells. “This can actually be quite useful for health care professionals as we will instantly know that something is wrong, and out of balance. Patients who have any infection within the mouth, have an instantly recognisable odour. I can often smell fulminant tonsillitis before I even examine someone.”

Those with gum infections, oral thrush and pharyngitis can, at times, have bad breath, while there are specific smells associated with some conditions which are not really described as 'bad breath' but certainly have an unpleasant smell, adds Dr Evans-Howells.

“For example, those with type I diabetes with very high blood sugars can often have a smell which warns us their sugars are worryingly high. It's not unusual that when people become dehydrated – often with an acute illness, they smell 'ketotic'.”

Solve it:

“Anyone who has a persisting change to the way their breath smells, should see a doctor and/or dentist, to check there are no underlying conditions,” advises Dr Evans-Howells.

Reason 7: You’re taking certain medications

Some common medications, like antihistamines and antidepressants, can cause dry mouth or release chemicals that contribute to bad breath.

“Any medication which is responsible for reducing saliva production in the mouth (as a side effect) could increase the risk of bad breath occurring. Common examples include amitriptyline (often used for chronic pain), antidepressants, sedatives and even sometimes antihistamines,” says Dr Evans-Howells.

“Additionally, steroid medication – like inhalers for asthma – will increase the risk of oral thrush occurring, particularly if individuals have not been trained how to use them correctly and do not rinse their mouth out after use.”

Solve it:

If dry mouth or bad breath is a side effect of your medication that’s causing you concern, talk to your doctor about possible alternatives or solutions. Using a saliva substitute or chewing sugar-free gum may help relieve dry mouth and freshen your breath.

By identifying the root cause of bad breath and addressing it with the right oral hygiene practices, lifestyle changes, or medical treatment, you can significantly improve the freshness of your breath. The biggest cause of bad breath is poor oral hygiene, so nailing that brushing routine, flossing daily and regularly visiting your dentist could help freshen it up.

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