Bad Breath and Their Causes


A lot of people suffer from chronic bad breath or ( Halitosis) , but many don’t seek help because they’re embarrassed. Although bad breath is often caused by oral problems, other bad breath causes are associated with other health problems. And bad breath can be a sign of serious disease.

Studies suggest 5-10% of bad breath causes are due to disease outside the mouth. That’s 2-5 million people whose bodies are warning them of a serious problem.

Dental disease and bad breath

90% of bad breath comes from proteins broken down in your mouth. When bad breath is caused by oral problems, it usually smells like rotten eggs. This is caused by the breakdown of cysteine at the front of the tongue or on the gums. It’s a sign of poor oral hygiene.

If you have bad breath, your first step is a dental exam and good oral hygiene. However, the mouth-body connection means that other bad breath smells can tell you about problems elsewhere in your body.


7 Causes of Bad Breath: Tooth Decay Smell, Cavities, and More

If you suffer bad breath the cause is most likely in your mouth. Conditions like tooth decay smell, cavities, or gum disease can all be bad breath causes.

Troubled with bad breath? It’s an embarrassing and frustrating problem. Luckily there are many easy solutions to chronic bad breath. One of the first ways you should look for a cure for bad breath is to see your dentist. Bad breath is often caused by oral diseases.

Ninety percent of cases of bad breath, or halitosis, actually originate in the mouth. The first port of call to cure bad breath is to see your dentist.

Bad breath causes that begin in the mouth:

  • Tooth decay smell and cavities
  • Failed dental work
  • Gum disease
  • White-coated tongue
  • Dry mouth (or low salivary flow rate)
  • Oral infections
  • Peri-implant disease
  • Oral cancer

Most dental diseases are caused by imbalances in your oral microbiome. In most cases, they are due to an overgrowth of ‘harmful’ bugs that release metabolites. This produces an odour that can be smelt on the breath.

Bad Breath Cause #1: Tooth Decay Smell and Cavities

Bad breath may signal tooth decay smell.  Initially, bacteria effect the hard outer enamel of your tooth. As bacteria burrow deeper into the softer inner tooth, the species causing the decay change.  E. faecalis, commonly found in the colon, and A. actinomycetemcomitans become prominent. Their presence changes the products released into your mouth.

Bad Breath Cause #2: Failed dental restorations

Have you had dental restorations, crowns or bridges? Decay or food traps beneath them may cause bad breath. You may notice a bad taste too. Visit your dentist, who will investigate with x-rays or radiographs to reveal underlying conditions. This cause of bad breath can not be discarded, it is as common as tooth decay smell and the ones that follow.

Bad Breath Cause #3: Gum disease

Gum disease progresses through different stages, which may all cause bad breath.  Let’s look at the stages of bleeding gums and gum disease.


a) Early-stage gum disease: ‘Food Caused’ bad breath

In early stage gum disease or bleeding gums, a buildup of plaque and calculus occur. This eventually causes enlarged gum ‘pockets’ (spaces between your teeth and gums). Food debris becomes trapped in the spaces between the teeth and gums. Bacteria find and eat these trapped food particles which can cause bad breath. Foods that contain dense proteins such as meats, dairy or fish, are broken down to pungent volatile sulfur compounds (VSCs).

2 types of early stage ‘food caused’ bad breath

  • Rotten Eggs: Cysteine breaks down to hydrogen sulfide, which smells like ‘rotten eggs’.
  • Rotten Cabbage: The protein methionine (commonly found in meat, eggs, and dairy) breaks down to methyl meth mercaptan, which smells like rotten cabbage.

As gum disease worsens, the bacteria in these pockets become more harmful. A particular type, called anaerobes, thrive in the absence of oxygen. Their presence is a sign that your gum disease is later stages may also cause bad breath.

b) Late stage gum disease: ‘Blood caused’ bad breath  

As gum disease progresses, both the pH and oral microbiome changes. In this stage, bad breath can worsen. Increased inflammation from bleeding gums provides a nastier set of ‘anaerobic’ bacteria access to blood and immune cells. These bugs thrive on an alkaline pH in the gum pocket. They then feed blood and immune cells.

Bad breath is now caused less by food breakdown and more by a mixture of decaying immune and blood cells. It means that the smell changes too.

2 types of ‘blood caused’ bad breath

  • Metallic smell or taste: Initially, as the iron in the blood breaks down, you may notice a metallic smell or taste.
  • Putrid or ‘rotten smell: As gum disease worsens, or is left untreated, the smell becomes far more putrid smelling.

In these more serious cases of gum disease, periodontal treatment is often helpful in halitosis (severe bad breath). Removal of the harmful microbiota  may only be achieved by dental root planning. It’s important to identify the root cause of your bad breath.

Bad Breath Cause #4: Tongue Coating

In some cases, neither your teeth or gums are unhealthy, or the cause of your bad breath. Instead, the culprit is your tongue.

Your tongue’s bumps and grooves are ideal for trapping debris and bacteria.

Just like bacteria like to hide in pockets in your gums, they also like to hide in the crevices of your tongue. A tongue coating is similar to dental plaque and can cause bad breath.  The coating appears on the top surface of the tongue. It’s usually towards the back of the mouth, near the throat.  It looks like a pale, white coating.

Tongue coating can be a mixture of sulfur compounds and mucus. It can also include food particles, coffee or tea, and bacteria. If it’s not cleaned away every 24 hours, bacteria can begin breaking these products down and cause bad breath.

In the same way, gum disease can cause bacterial imbalance, so can your tongue coating.  As anaerobic bugs infiltrate, they cause bad breath. Many studies have shown that removing this tongue coating reduces bad breath and VSC levels.

If you suspect your tongue is causing your bad breathtry cleaning the dorsum (top surface) of the tongue regularly with a tongue cleaner.


Bad Breath Cause #5: Dry mouth or low saliva  

Saliva performs many functions, including balancing minerals and aiding the digestive system and immune system.

Saliva contains immune factors known as IgA and other factors called lysozymes. These help healthy digestion and also prevent the buildup of harmful bacteria. In a healthy mouth, saliva helps to maintain the oral pH at slightly acidic. This prevents harmful bacterial buildup and the breakdown of proteins such as cysteine and methionine. These proteins create sulfur containing compounds (VSCs) and cause bad breath.

When your salivary flow rate is low, you lose the benefit of saliva’s cleansing abilities. The environment in your mouth becomes alkaline, allowing the growth of harmful bacteria and those that break down VSCs.

So, what might affect your salivary flow rate and cause a dry mouth?

Diseases that affect the salivary glands, such as Sjogren’s Syndrome, certain medications and breathing through your mouth may all cause dry mouth.

The most common type of bad breath caused by saliva flow problems is ‘morning breath’ – bad breath that’s only present when you wake up. This is usually due to decreased production of saliva while you are asleep but may also indicate you are breathing through your mouth during the night.

Bad Breath Cause #6: Oral Infections

Dry Socket

After a tooth extraction, a blood clot normally forms to begin the healing process. Dry sockets occur when the blood clot is lost from the socket. This can happen because of negative pressure in the mouth, perhaps from sucking on a straw or smoking, which prevents clot formation. The resulting exposed wound may be very painful – and more painful than the original toothache.

This condition can cause both a bad taste and bad breath due to trapped food debris and bacteria. One of the most common signs of a dry socket, other than gum pain, is bad breath.  Large dry sockets can take weeks or even months to heal completely. They usually require irrigation after every meal to prevent food particles from lodging in them and festering.


When teeth are erupting in the gums, the slightest opening in your gum can allow saliva and bacteria into the space around the tooth. If the space can’t cleanse itself, you may find yourself with an infection.

This condition is called pericoronitis (infection in the soft tissues around the crown of the tooth).  It may cause just mild pain or a dull ache, but sometimes the area may become very painful and swollen. If your gum is red and inflamed around a tooth that hasn’t fully erupted, and you have a bad taste in your mouth and bad breath, you may have pericoronitis.


Peri-Implant Disease

In peri-implant disease, inflammation occurs in the soft tissues around a dental implant. Generally, peri-implant mucositis (inflammation of gums) is a precursor to peri-implantitis where there is bone loss around a dental implant. If you’ve had an implant and have bad breath or an unpleasant taste in your mouth, it may be a sign of peri-mucositis. You should see your dentist straight away.

Mouth Ulcers

Mouth ulcers can occur on the lips, tongue or, more commonly, the inside of the cheeks.  They will look swollen and may be white, red, yellow or gray.  It’s possible to have more than one mouth ulcer at a time and they may spread or grow.

Mouth ulcers can occur due to:

  • Physical damage: wear and tear, biting your cheek or tongue, or puncture wounds caused by foods with sharp edges such as crisps.
  • An allergic reaction or auto-immune system response to chemical or biological agents. The primary damage happens underneath the surface, causing cells to die within the connective tissue. When the damage reaches the surface, the ulcer seems to appear from nowhere.
  • Inflammatory or infectious disorders, and cutaneous, gastrointestinal, and hematological diseases.

Oral Causes of Bad Breath Screening Questionnaire

Most cases of bad breath are caused by disease in the mouth. Often it can be improved by a visit to the dentist and improved oral hygiene. However, sometimes bad breath originates from a problem elsewhere in the body (like the nose or the digestive system).

So, how can you tell if your bad breath originates from your mouth? Or should you be visiting your doctor?

If your bad breath is more likely to originate in your mouth if:

  • It is improved by the regular use of mouthwash (I don’t recommend mouthwash for bad breath)
  • It is improved by better oral hygiene and tongue brushing.
  • The odor does not exit from the nostrils.
  • The odor intensifies for an observer when you begin to talk, indicating that the odor is
  • coming from the mouth rather than the nose. Your pharmacist may ask you to count to 20 while they check your breath for this.
  • The odor worsens if the mouth becomes dry, as the buffering effect of saliva is lessened
  • and non-sulfur containing gases are liberated when oral tissue is dry.
  • You lick your hand and there is a detectable odor when the saliva dries.
  • You scrape the back of the tongue gently with a disposable plastic spoon and the residue on the spoon smells the same as your breath.

If you have bad breath, the first step you should take is to book in to see your dentist.

Types of systemic diseases bad breath

If you or your dentist can identify the type of smell in your bad breath, this can help to pinpoint its origin. This oral-systemic link means your dentist may identify potential problems elsewhere in your body – just as an optician can by examining your eyes.

Here are the types of smells different systemic disease bad breath:

  • cheesy smell usually indicates your bad breath has a nasal origin.
  • A  fruity smell may indicate uncontrolled diabetes due to increased
  • A  fishy smell may indicate kidney disease, as increased urea levels can cause a fishy smell such as in  (trimethylaminuria)
  • An acidic smell can be a sign of asthma or cystic fibrosis
  • A  scent of ammonia can indicate kidney problems
  • A  sweet, musty odor may signal liver cirrhosis
  • A  fecal odor may point to a bowel obstruction

There are 12 types of ‘bad breath’ caused by disease in your body

  • Tonsil breath
  • Sinus breath
  • Lung breath
  • Gut breath
  • Metabolic breath
  • Diabetes breath
  • Drug breath
  • Liver breath
  • Trimethylaminuria breath
  • Menstrual breath
  • Drug-induced bad breath
  • Halitophobia


So, why does bad breath matter?

Firstly, as we’ve seen, bad breath can be a clue to poor oral health and hygiene.

Secondly, halitosis – severe bad breath – can indicate a disease elsewhere in the digestive system and other organs.

Has your dentist identified a general health issue or are you suffering from bad breath?

Let us know your issues with bad breath.

If you feel that you are suffering from bad breath or halitosis, do not hesitate to consult Dr.Miski, a specialist Periodontist (Gum Specialist) to tackle this problem.