Bad Breath (Halitosis): Causes and What Actually Helps

Bad breath is usually caused by bacteria on the back of the tongue and along the gums, which break down proteins into foul-smelling sulfur gases [1, 2]. Dry mouth, strong foods and smoking make it worse [3]. A smaller share of cases come from the nose, throat or a medical condition elsewhere in the body [2].

What is halitosis?

Halitosis is the medical term for bad breath [4]. A review of 13 population studies put the pooled prevalence at about 32% of adolescents and adults, though results varied widely [5]. The smell comes mostly from volatile sulfur compounds (VSCs) such as hydrogen sulfide and methyl mercaptan, which bacteria release as they break down sulfur-containing amino acids [2]. Morning breath is normal, because saliva flow drops during sleep [3].

The largest clinic study we found looked at 2,000 consecutive patients in Leuven, Belgium [1]. The table shows the main causes, and other or mixed causes make up the remainder:

The main bad breath causes

The tongue

The coating on the back of the tongue is the most important source of VSCs [2]. We compare the tools for removing it in tongue scraping vs tongue brushing.

Gums and teeth

Periodontal pockets are a reservoir for odor-producing bacteria [2]. People with periodontitis had about three times higher odds of halitosis across five pooled population studies, though these were cross-sectional and cannot prove cause [6]. Cavities, mouth infections and poorly cleaned dentures can also cause odor [3, 4].

Dry mouth

Saliva rinses away food and bacteria, so less saliva means more odor. Common causes of a dry mouth include some medicines, smoking and certain health conditions [3, 7].

Food, fasting and smoking

Garlic, onions and spices are absorbed into the blood and carried to the lungs [3], and fasting or crash dieting can also cause bad breath [4]. Tobacco leaves its own smell, dries the mouth and raises the risk of gum disease [3, 7], and smokers tend to have more tongue coating [8].

Causes outside the mouth

About 5 to 10% of halitosis starts outside the mouth [2]. Causes include tonsil stones, postnasal drip, infections of the nose, throat or lungs, acid reflux (GERD), kidney or liver disease, some head and neck cancers, and diabetes [3, 7]. Breath that smells fruity in someone with diabetes can be a sign of ketoacidosis, which is a medical emergency [7].

When to see a dentist or doctor

See a dentist if bad breath does not go away after a few weeks of better cleaning at home, or if you have painful, bleeding or swollen gums, toothache or loose adult teeth [4]. If your dentist finds no cause in the mouth, see your doctor to look for one elsewhere [3, 7].

How to get rid of bad breath: what the evidence supports

Clean between your teeth every day

The NHS and Mayo Clinic both advise cleaning between your teeth once a day with floss or interdental brushes [4, 9]. In a five-week trial of people with treated periodontitis, interdental brushes and rubber picks reduced plaque and gum inflammation more than a toothbrush alone [10]. Few trials measure breath after flossing, so the case rests on gum health, and our guide to cleaning your gums naturally covers technique.

Clean your tongue

A systematic review found that adding tongue cleaning to toothbrushing reduced breath odor and tongue coating [11], but the effect is short-lived and the 2019 Cochrane review rated the evidence as very low certainty [12].

Stay hydrated

Mayo Clinic recommends drinking plenty of water and chewing sugar-free gum to keep saliva flowing [9], though we did not find large trials testing hydration as a treatment for bad breath.

Choose a mouthwash by its ingredients

In the 2019 Cochrane review, brushing plus a cetylpyridinium chloride (CPC) mouthwash lowered odor scores more than brushing alone, but that rested on one trial of 70 people and was rated low certainty [12]. A separate review found the most support for rinses combining chlorhexidine, CPC and zinc, or zinc chloride and CPC, yet graded the recommendation as weak [13]. Chlorhexidine can temporarily stain the teeth and tongue and change how things taste [14].

Bad breath myths

• Myth: you can check your breath by breathing into your hand. In 626 Swiss army recruits, self-reported bad breath did not match clinical measurements [15], and an earlier study found that expectations skew how people score their own breath [16].
• Myth: bad breath usually comes from the stomach. Only 4% of the 2,000 clinic patients had an ear, nose, throat or other cause outside the mouth [1], although reflux can contribute [3].
• Myth: brushing removes garlic breath. In a small study of five people who ate garlic, the odor came first from the mouth, but after three hours the main sulfur gas came from the gut, where brushing cannot reach [17].
• Myth: natural remedies are proven fixes. A 2021 review of 26 studies on alternative treatments such as herbal products and essential oils found inconsistent results, a high risk of bias throughout and no clear evidence of added value [18].

Where a miswak fits

A miswak is a tool for cleaning teeth and gums, used alongside a regular toothbrush and dental checkups. The miswak contains silica (a natural abrasive), trace natural fluoride, benzyl isothiocyanate (germ-killing compounds released when chewed), tannins, vitamin C, salvadorine and trimethylamine [19, 20]. In lab tests, benzyl isothiocyanate quickly killed Gram-negative bacteria linked to gum disease [21], which we cover in the natural compounds in a miswak.

The breath evidence is thin: in a seven-day trial of 34 women with bad breath, judge-rated odor scores fell in groups using a miswak, a miswak extract rinse or a chlorhexidine rinse, but breath-meter readings did not change significantly and no comparison between groups was reported [22]. In a survey of 1,551 adults in Kuwait, people who never used a miswak were more likely to report bad breath, an association that cannot prove cause [23]. For more on the miswak and breath, see does miswak remove bad breath.

Frequently asked questions

If you want to add a miswak to your routine, start with the 1 Pack or the Family 4 Pack; one stick lasts 1 to 3 months, and 20% of our profits go to humanitarian aid.