The biggest myths about bad breath
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"Frankly my dear, I don't give a damn about oral hygiene" (Credit: Alamy)
Claudia Hammond analyses the science, the misconceptions – and what you may be doing wrong.

Many years ago, soon after I’d started working in radio, I arrived at the newsroom to be given my assignment for the day. I was asked to visit a clinic treating bad breath where I was to get my own breath tested and interview the doctor.

On the way there I did wonder whether this was all a ruse and whether there was something my colleagues were too afraid to tell me. Luckily I was fine, but bad breath is common and we’re not helped by some of the myths surrounding it.  


The problem with this method is that breathing into your hands doesn’t propel breath out from the back of your mouth in the same way that happens when you talk. So when you breathe into your hand you might miss out on the smells from the gases produced at the back of your tongue, the main place where bad breath originates.

Doctors assess bad breath by sniffing it a few centimetres from a patient’s face

Doctors have three methods for testing for bad breath. They can assess it themselves by sniffing one of the following: the patient’s breath just 5cm (2in) from the nose of the doctor, the contents of a spoon which has been scraped across the top of the tongue, unwaxed floss which has been passed between the back teeth or a petri dish containing the patient’s saliva that’s been left in an incubator at 37C (99F) for five minutes.

It's wise to brush those gnashers regularly to avoid whiffy breath, even if you're a hippo at London Zoo (Credit: Getty Images)

It's wise to brush those gnashers regularly to avoid whiffy breath, even if you're a hippo at London Zoo (Credit: Getty Images)

There are also small monitors available which can detect certain gases, but the limitation here is that it only includes some gases and not others. Finally ‘gas chromatography’ – a technique to separate complex mixtures of gases – can measure the quantity of sulphur in the air, but involves specialised equipment that you won’t find in many doctors’ offices.

Not everyone who thinks they have bad breath, does. They misinterpret people stepping back or turning away when in real cases of halitosis this isn’t the way people tend to react. One study put this proportion at 27%

There is no agreement on what proportion of the whole population does actually have halitosis, with rates varying from 22 to 50%.


Most of the bad smell comes from volatile sulphur compounds, gases with distinctive odours. Hydrogen sulphide, with its classic rotten eggs smell is one of the main offenders, but even worse is a substance called ethyl mercaptan which tends to be described as smelling of decomposing cabbage. It’s the compound which makes some people’s urine particularly pungent after they’ve eaten asparagus.

Ethyl mercaptan tends to be described as smelling of decomposing cabbage

These compounds are given off when food and bacteria accumulate in the furrows at the back of the tongue. The good news is that this can be temporary, as a result of eating garlic or raw onions, drinking coffee or smoking cigarettes. But in three quarters of cases some kind of dental problem is found alongside the halitosis. The patients might have gums which are swollen, sore or infected or be suffering from a coating on the tongue.

It is true that in a small percentage of cases bad breath is caused by a problem elsewhere in the body such as the ear, nose and throat, kidneys, lungs or intestines, but when this does happen it’s unusual for halitosis to be the only symptom.


The first thing many people do if they suspect they have bad breath is to reach for the mouthwash. The mint or clove flavouring does of course, disguise the smell for a short time, and many mouthwashes also contain antiseptic. The idea is to eliminate the bacteria that leads to foul-smelling compounds. For a time this can work. But there has been some debate concerning containing alcohol and whether it does or doesn’t exacerbate dehydration. A very dry mouth can cause breath to smell worse.

Drinking more water during the day can help, both by rinsing away food and preventing dryness in the mouth.

Mouthwash - not always effective (Credit: Getty Images)

Mouthwash - not always effective (Credit: Getty Images)

The UK health research body Cochrane is currently assembling a review of the scientific literature on interventions for bad breath. In their previous review of mouthwashes in 2008, the five best trials showed that if they contained anti-bacterials such as chlorhexidine and cetylpyridinium chloride, chlorine dioxide or zinc, they could reduce unpleasant smells to an extent. But the authors did call for more trials to be done.  Hopefully this next review will be able to give more information about which mouthwashes to choose.

The alternative is to scrape your tongue with a special tongue cleaner. This method is also under assessment in the newest Cochrane review. Their last report found just two small trials looking at this method. They showed it can work, but that the effect is short-lived. They also highlight the risk of damaging the tongue by pressing too hard and to ensure that if you want to use a toothbrush to clean your tongue, you make sure that it’s a soft one.


Every individual has a slightly different community of between 100-200 microbes in their mouth. As we are coming to appreciate the human microbiome and the positive role that the millions of bacteria present in our bodies can play, instead of eliminating bacteria from the mouth altogether, scientists are trying to work out how to get the right combination, by targeting specific bacteria for elimination or using probiotics to encourage certain bacteria in the mouth.

Phase I and II trials have already been conducted into killing the bacteria most often implicated in tooth decay. The substance has been trialled as a gel applied in a clinic and next it will be tested as a varnish, again applied in a clinic, but accompanied by strips which people can take home and apply to their teeth as a follow-up treatment. This opens up the possibility in the future for using similar methods to target the bacteria most often implicated in bad breath.

It’s early days, so for now the medical advice is to brush and floss your teeth carefully, to drink plenty of water, not to smoke, to eat a balanced diet and to see your dentist about bad breath in case you have early signs of gum disease. 


The team from the BBC TV series 'Trust me I’m a doctor' spoke to dentists about how to spot and avoid bad breath. Watch the video below for their tips:

Trust me, I'm a doctor- Bad breath

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