What the smell of your BREATH says about you, according to science

Daily Mail​

26-07-2025

From the ridges on your fingernails to the colour of your tongue, there are plenty of signs that something might be wrong with your health.
Now, an expert has revealed the smell of your breath is something to keep an eye on, too.
Many might assume that bad breath – also known as halitosis – is the result of poor teeth cleaning or drinking too much coffee.
However, research suggests breath odour may be an early warning sign of systemic health issues.
Certain scents could indicate diabetes, while others could point to liver dysfunction.
'Your breath can offer a surprising window into your health,' dental technologist Allen Zhang said.
He said there are five commonly overlooked types of breath that could signal a health issue.
So, do you recognise any of them?
FRUITY OR ACETONE-LIKE
This odour could indicate poorly-controlled diabetes, Mr Zhang explained.
Research suggests that fruity-smelling breath can be a sign of high ketone levels in the blood, which can occur in individuals with the condition.
Those affected might have breath that smells like pear drop sweets or nail polish remover.
METALLIC
This smell could suggest someone is suffering from kidney dysfunction or heavy metal exposure.
This symptom arises when the kidneys are unable to effectively remove waste from the body – including urea, which forms ammonia when mixed with saliva.
The presence of ammonia in breath can sometimes be perceived as having a metallic tinge.
FISHY
A fishy-smelling breath could indicate a condition called trimethylaminuria, Mr Zhang said.
This is a metabolic disorder where the body cannot break down trimethylamine, a compound that smells like rotten fish.
Fishy breath can also be a symptom of liver problems, specifically related to a condition called fetor hepaticus.
Fetor hepaticus, often described as 'breath of the dead', arises when the liver is unable to properly filter certain toxins from the blood.
These toxins, like dimethyl sulphide, can build up in the blood and be exhaled, causing the characteristic odour.
Breath that smells sulphurous or like rotten eggs, can be an indicator of gastrointestinal issues. The smell is called by hydrogen sulphide gas, which can be produced during digestion.
MUSTY
Finally, musty breath could mean there is something wrong with your kidneys or be a sign of liver failure.
'These are diagnostic clues and not just hygiene red flags,' Mr Zhang said.
'New tech is emerging to help clinicians detect disease risk via oral biosignatures, including volatile sulphur compounds and ketones in the breath.'
Mr Zhang is the founder of ProDENT, a company developing intraoral imaging solutions for early detection.
CAUSES OF BAD BREATH (HALITOSIS)
There are a number of possible causes of halitosis:
Poor oral hygiene
This is the most common cause. Bacteria that build up on your teeth – particularly between them – as well as your tongue and gums, can produce unpleasant-smelling gases. These bacteria are also responsible for gum disease and tooth decay.
Food and drink
Eating strongly flavoured foods, such as garlic, onions and spices, is likely to make your breath smell. Strong-smelling drinks, such as coffee and alcohol, can also cause bad breath.
Bad breath caused by food and drink is usually temporary. Good dental hygiene will also help.
Smoking
As well as making your breath smell, smoking stains your teeth, irritates your gums, and reduces your sense of taste.
It can also significantly affect the development of gum disease, another major cause of bad breath.
Crash dieting
Crash dieting, fasting, and low-carbohydrate diets are another possible cause of bad breath. They cause the body to break down fat, which produces chemicals called ketones that can be smelled on your breath.
Medication
These include: nitrates – these are sometimes used to treat angina; some chemotherapy medication; and tranquillisers (phenothiazines).
If the medication you're taking is causing bad breath, your GP may be able to recommend an alternative.
Medical conditions
In rare cases, bad breath can be caused by certain medical conditions. In dry mouth (xerostomia), the flow and composition of saliva may be affected.
Dry mouth can sometimes be caused by a problem in the salivary glands or by breathing through your mouth instead of your nose.
In some cases, gastrointestinal conditions can also cause bad breath. For example, a bacterial infection of the stomach lining and small intestine (H. pylori infection) and gastro-oesophageal reflux disease (GORD) have been linked to bad breath.
Other medical conditions that can cause bad breath include diabetes and lung, throat, or nose infections – for example, bronchiectasis, bronchitis, tonsillitis, and sinusitis.