Halitosis (Bad Breath): Causes and What to Do

The most common cause of bad breath (halitosis) is a build-up of bacteria in the mouth — particularly on the back of the tongue — along with gum disease, tooth decay and a dry mouth. The vast majority of cases originate in the mouth and can be managed with good hygiene. If persistent odour does not improve after a professional cleaning, it may point to an underlying problem and should be assessed by a dentist.

What does the research show? Around 85–90% of halitosis cases originate within the mouth — tongue coating, periodontitis, caries and a dry mouth, where bacteria produce volatile sulphur compounds (International Journal of Oral Science, 2012); contrary to popular belief, gastrointestinal causes rarely play a role, while among non-oral causes, ear, nose and throat and sinus problems are more common. According to a Cochrane review (2019), mechanical tongue cleaning, antibacterial mouthwashes and professional periodontal treatment are effective in the short term, while long-term evidence is limited. If odour persists (for more than 2–3 weeks) and does not resolve at home, a professional assessment is needed. Related: Professional cleaning · Tongue cleaning · The difference between tartar and plaque.

What is halitosis?

Halitosis is the medical term used to describe persistent bad breath. Temporary odour on waking in the morning (caused by a dry mouth overnight) is normal and usually goes away after brushing. Persistent odour that stays throughout the day, however, calls for the underlying cause to be identified. Very often the person with the odour cannot smell it themselves — those around them notice it more easily.

Main causes

The leading causes of bad breath are:

• A layer of bacteria on the tongue — the most common source of odour; food debris and bacteria collect on the back of the tongue.
• Poor oral hygiene — plaque and food debris that are not brushed away.
• Gum disease (gingivitis/periodontitis) — inflamed gums create odour.
• Tooth decay — bacteria building up in cavities.
• Dry mouth (xerostomia) — when saliva decreases, the mouth cannot clean itself naturally.
• Food and habits — garlic, onion, coffee, smoking and alcohol.
• Non-oral causes — sinus and ear, nose and throat infections, stomach conditions or certain systemic diseases (less commonly).

What to do at home

Most cases improve with the right home care:

• Clean your tongue: Gently clean the back of the tongue with a tongue scraper or brush — this is one of the most effective steps.
• Correct brushing and interdental cleaning: Brush twice a day and use interdental floss. For technique, see our article on correct brushing and flossing.
• Drink water: Keeping the mouth moist supports saliva in its natural cleansing role.
• Give up tobacco: Smoking both creates odour and increases the risk of gum disease.
• Consider dietary factors: The effect of foods such as garlic and onion is temporary.

Mouthwashes can mask odour temporarily, but they do not address the cause — the main focus should be on hygiene.

When to see a dentist

• Odour that persists despite good hygiene
• Odour accompanied by bleeding, swollen or receding gums
• A persistent bad taste in the mouth
• A constant feeling of dry mouth

A dentist can identify the cause — tooth decay, gum disease or tartar. Professional tartar removal often makes a significant difference. If odour continues after oral causes have been ruled out, a referral to your family doctor may be considered.

Points to keep in mind

• In most cases halitosis originates in the mouth and can be managed.
• Cleaning the tongue is an often overlooked yet effective step.
• Mouthwash does not address the cause, it only masks it temporarily.
• Persistent odour should be assessed by a dentist.

Questions and Answers (FAQ)

What is the most common cause of bad breath? The most common cause is a build-up of bacteria in the mouth, particularly on the back of the tongue. Gum disease, tooth decay and a dry mouth are also frequent causes. Most cases originate in the mouth and are managed with hygiene.

Why does my breath smell even though I brush? The cause is often a layer of bacteria remaining on the back of the tongue, or areas between the teeth that are not being cleaned. Gum disease, hidden decay or a dry mouth may also play a part. Cleaning the tongue, using interdental floss and having a professional check-up all help.

Does mouthwash solve halitosis? Mouthwash can mask odour temporarily, but it does not eliminate the underlying cause — bacteria, plaque or gum inflammation. Lasting results require good hygiene and, where necessary, an examination by a dentist.

Can bad breath be a sign of a serious illness? In most cases no — the cause originates in the mouth. In rare cases, however, persistent odour may be linked to a sinus infection, conditions that cause a dry mouth, or systemic diseases. Odour that continues after oral causes have been ruled out should be investigated by a doctor.

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Clinical note: This article is for general information only and does not replace individual advice from your dentist. To discuss persistent bad breath, book an appointment.

Sources: Peer-reviewed dental literature on oral hygiene, periodontology and the management of halitosis. The clinical content is based on Dr. Minaya's dentistry practice.