What are the most common causes of bad breath (halitosis)?

Last updated on: 5 Aug, 2026

Bad breath is most often caused by poor oral hygiene, a build-up of bacteria, gum and tooth disease, dry mouth, dietary habits or systemic health problems, as halitosis is usually a symptom rather than a condition in its own right.

Unpleasant mouth odour is an issue that affects millions of people worldwide. It can be temporary and harmless, but in other cases it is a sign of an untreated health problem. In medicine, this condition is known as halitosis and can occur episodically or chronically.

In this article, we will look at what bad breath is, what its most common causes are, and what steps you can take to deal with it. We will also look at the situations in which it is advisable to seek professional help.

Image: freepik

What is bad breath?

An unpleasant odour from the mouth is a problem that affects a significant proportion of people and impacts both self-esteem and daily social interactions. In medicine, this condition is known as halitosis and affects around 20–30% of the global population. 

Bad breath can occur occasionally, for example upon waking or after eating certain foods, but it can also be a chronic problem that signals a more serious health condition.

Halitosis is not a disease in itself, but rather a symptom. It can be caused by various factors, ranging from poor oral hygiene to diseases of the internal organs. This is precisely why identifying the causes and responding promptly are essential for successfully managing this problem.

What are the most common causes of bad breath?

The sources of unpleasant odours from the mouth can be varied. Some are linked to daily habits, whilst others are linked to specific health conditions. Here are the most common causes of bad breath that patients encounter.

Poor oral hygiene

The most common cause of unpleasant odour is poor oral hygiene. When teeth are not brushed regularly and properly, food debris remains between them and on the surface of the tongue. Bacteria in the mouth break down this debris and release volatile compounds that have a characteristic unpleasant odour.

Tartar build-up

If dental plaque is not removed in time, it mineralises and turns into tartar. The link between bad breath and tartar is direct – tartar creates an uneven surface on which food debris gets trapped and bacteria accumulate, causing an unpleasant odour. 

Gum and tooth diseases

Tooth decay, gingivitis and periodontitis are common causes of halitosis. When there is inflammation of the gums or damage to the tooth structure, bacteria multiply actively in the affected areas. 

The link between bad breath and the gums is well established – inflamed, bleeding gums are almost always accompanied by an unpleasant odour. The same applies to the link between bad breath and teeth with untreated cavities, pulpitis or gangrene.

Bacterial activity in the oral cavity

The mouth is home to hundreds of species of microorganisms. When the balance is disrupted, the number of anaerobic bacteria that produce hydrogen sulphide and methyl mercaptan increases. It is precisely bad breath and bacteria that go hand in hand – the greater the bacterial colonisation, the stronger the unpleasant odour.

Dry mouth (xerostomia)

Saliva performs an important protective function – it washes away food debris and neutralises acids in the mouth. When saliva production is reduced, conditions become favourable for bacterial growth. Bad breath and xerostomia are closely linked, and dry mouth can be a result of taking certain medications, mouth breathing or systemic diseases.

Bad breath in the morning

Almost everyone has experienced bad breath in the morning after waking up. During sleep, saliva production decreases significantly, allowing bacteria to multiply unchecked. 

This is a normal physiological phenomenon that usually goes away after brushing your teeth and having breakfast. However, if the unpleasant morning odour is extremely strong or does not go away easily, there may be another cause.

Dietary habits

Certain foods are known to cause bad breath. Garlic, onions, spices and some types of cheese contain sulphur compounds that are absorbed into the bloodstream and released through the breath. 

Bad breath caused by food is usually temporary and clears up within a few hours. More generally, bad breath and foods that are high in protein and low in carbohydrates can also cause ketone breath.

Smoking

The link between bad breath and smoking is indisputable. Tobacco smoke contains over 7,000 chemical compounds, many of which linger in the mouth. Smoking dries out the mucous membranes, reduces saliva production and increases the risk of gum disease. All of this creates the conditions for chronic halitosis.

Alcohol consumption

Alcoholic drinks have a drying effect on the oral mucosa. With regular consumption, bad breath caused by alcohol can become a constant companion. Alcohol also disrupts the normal microflora of the oral cavity and stomach, which further exacerbates the problem.

Digestive problems and gastritis

The cause of an unpleasant odour is not always in the mouth. Bad breath and stomach problems are linked more often than most people realise. Gastro-oesophageal reflux, for example, allows stomach acid and gas to reach the oral cavity. Bad breath and gastritis can also go hand in hand. 

Low-calorie and high-protein diets

People who follow strict diets sometimes notice the development of a specific odour. The link between bad breath and diet is due to the process of ketosis. When the body uses fat as its main source of energy, ketone bodies are released, which have a characteristic sweetish smell of acetone.

Systemic diseases and infections

Certain conditions outside the oral cavity can also cause halitosis. Bad breath and diabetes are linked due to diabetics’ tendency towards dry mouth and increased susceptibility to gum infections. Bad breath and upper respiratory tract infections, sinusitis or chronic tonsillitis also cause a characteristic unpleasant odour.

How can we tackle bad breath?

Tackling halitosis requires a comprehensive approach. Depending on the cause, different measures are needed, but the good news is that in most cases the problem can be resolved. Here are the most effective methods for achieving fresh breath.

Improving daily oral hygiene

The first and most important step is to learn how to get rid of bad breath through proper hygiene. Brush your teeth at least twice a day with a high-quality fluoride toothpaste. Don’t neglect your tongue – a large amount of bacteria accumulate on its surface. Use dental floss or interdental brushes to clean the spaces between your teeth where your toothbrush cannot reach.

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Regular check-ups

Preventing bad breath involves visiting the dentist at least twice a year. Professional removal of tartar and plaque significantly reduces the bacterial load in the mouth. At DentaTime, we have an ultrasonic device and an Air Flow system for gentle and effective cleaning, which are part of our comprehensive approach to preventing bad breath.

Image: freepik

Hydration and stimulating saliva production

Drinking enough fluids throughout the day keeps the mouth moist and aids the natural self-cleaning process. If you suffer from a dry mouth, bad breath and sugar-free chewing gum is a useful combination – chewing stimulates saliva production and helps wash away food debris. Another tip for fresh breath is to drink more water between meals.

Natural remedies and probiotics

Natural remedies for bad breath include chewing fresh parsley or mint, or drinking green tea, which can temporarily freshen your breath. In recent years, experts have also focused on the link between bad breath and probiotics, which help restore the oral microflora.  

Treatment of the underlying condition

If halitosis is a symptom of another condition, treating it involves addressing the underlying problem. For gum disease, periodontal treatment is necessary. For tooth decay, the affected teeth need to be restored.

When can bad breath be a more serious problem?

Chronic halitosis can be a sign of untreated periodontitis, diabetes, kidney disease or stomach disorders. Bad breath and oral health are inextricably linked. 

If the bad breath is accompanied by bleeding gums, pain, loose teeth or a change in taste, it is advisable to seek dental treatment as soon as possible.

Conclusion

Halitosis is a condition that can be successfully managed, provided it is approached correctly. Do not underestimate bad breath; instead, treat it as a signal from your body that something needs attention. If the problem persists, consult a dental specialist for professional advice and a comprehensive treatment plan.

Frequently asked questions

Can stress cause bad breath?

Yes, stress reduces saliva production and can lead to a dry mouth, which creates conditions for bacteria to multiply and cause an unpleasant odour.

How often should I change my toothbrush?

It is recommended that you replace your toothbrush every 3 months, or sooner if the bristles are worn, as a worn toothbrush cleans significantly less effectively.

Do dentures affect breath?

Dentures can trap food debris and bacteria if not cleaned properly. Regular disinfection and removing them at night significantly reduce the risk of bad breath.