Oral health guide

What Causes Bad Breath (and What Actually Helps)

Almost everyone has bad breath now and then. When it sticks around, the cause is usually in the mouth, and the habits that help most are the unglamorous ones. Here’s what causes it, what the research says about popular remedies, and when it’s worth seeing a dentist.

Research last updated · Written by Sarwar Hossain

You’re far from alone. The American Dental Association (ADA) says studies show that 50 percent of adults have had bad breath, also called halitosis, at some point in their lives.[1] A 2019 Cochrane review put the figure at 50% to 60% of people worldwide.[2]

What causes bad breath

The main cause is bacteria in the mouth. Without regular brushing, cleaning between the teeth and professional cleanings, bacteria build up and produce bad smells, according to Cleveland Clinic.[3] The ADA notes that hundreds of types of bacteria that can cause bad breath live in the mouth naturally.[1] Other common causes:

  • The tongue. Bacteria and bits of food collect on the surface of the tongue, which is why cleaning it is often recommended.[3]
  • A dry mouth. Saliva washes food particles away from the teeth and gums. The National Institute of Dental and Craniofacial Research (NIDCR) says hundreds of medicines can make the salivary glands produce less saliva, and that dry mouth is not a normal part of aging.[4] The ADA lists dry mouth as a cause of bad breath.[1]
  • Food and drink. Garlic, onions and coffee are on the ADA’s list: what you eat affects the air you breathe out.[1]
  • Tobacco. Smoking stains teeth and causes bad breath, along with far more serious health risks.[1]
  • Gum disease. Bad breath that won’t go away, or a constant bad taste in your mouth, can be a warning sign of advanced gum disease.[1]
  • Other health conditions. Mouth infections can cause bad breath. If your mouth is healthy, the ADA says the cause could be something else, such as a sinus condition, gastric reflux, diabetes, or liver or kidney disease.[1]

What helps most: the everyday basics

Because most bad breath comes from bacteria in the mouth, the habits that keep your mouth clean do most of the work:

  • Brush twice a day with a fluoride toothpaste, and clean between your teeth once a day with floss or another interdental cleaner.[5, 1]
  • Clean your tongue with your toothbrush or a tongue scraper.[3]
  • Clean dentures or other removable appliances thoroughly before you put them back in.[1]
  • Keep your mouth moist. NIDCR suggests drinking plenty of water, sipping water with meals, chewing sugarless gum or sucking sugarless hard candy, and limiting caffeine.[4] The ADA also suggests crunchy foods that need a lot of chewing, such as carrots or apples.[1]
  • Skip tobacco. Giving it up helps your breath and much more besides.[1, 4]
  • See your dentist regularly. Checkups let your dentist spot problems such as gum disease or dry mouth early.[1]

Tongue scrapers and mouthwash: what the research says

The most thorough look at the evidence is a 2019 Cochrane review. It pulled together 44 trials with 1,809 people that compared ways of managing bad breath, including tongue cleaning, chewing gum, toothpastes and mouthwashes, against a placebo or no extra care.[2]

The results were underwhelming. Most trials lasted only one to four weeks, and only three of the 44 were judged at low risk of bias. The authors rated the evidence as low to very low certainty and couldn’t say that any one approach worked better than another.[2]

That doesn’t mean these things are useless. The ADA says over-the-counter mouthwashes can help kill bacteria or neutralize and temporarily mask bad breath.[1] In one trial in the Cochrane review, people who brushed and also used a mouthwash containing cetylpyridinium chloride had slightly better breath scores than people who only brushed, though the evidence was low certainty.[2]

The practical takeaway: a tongue scraper or a mouthwash is a cheap extra you can add, but neither replaces brushing, cleaning between your teeth and dental visits. A mouthwash that only masks odor may also hide a problem a dentist should look at.

Can probiotics help with bad breath?

Oral probiotics are supplements, usually lozenges or chewable tablets, that contain “friendly” bacteria. The idea is that they shift the balance of bacteria in the mouth.

A 2026 umbrella review in Frontiers in Oral Health, which combined 11 earlier analyses, found that probiotics were linked with modest improvements in bad-breath measures. The authors stressed that the effects depend on the specific strain and dose, that the certainty of the evidence is limited, and that routine use of probiotics to prevent oral disease should be considered experimental.[7]

One example of the kind of study behind these findings: in a four-week trial of 68 adults with bad breath, lozenges containing the strain Lactobacillus paracasei ET-22, taken three times a day, lowered the levels of the sulfur compounds that make breath smell bad.[8] It was a small, short study of one strain, so it doesn’t tell you whether a different product, with different strains or doses, would do the same.

If you’re thinking about an oral probiotic, check the label for the full strain names and the amount of each, and compare them with the studies. Our guide to reading a supplement label shows how, and our research review of ProDentim applies the same checks to one oral probiotic. Either way, a probiotic is at most an optional extra on top of the basics above.

When to see a dentist or doctor

Bad breath is usually harmless, but it can be a sign of a problem worth checking. See a dentist if:

  • You brush and clean between your teeth well, and the bad breath still doesn’t go away.[3]
  • You have a constant bad taste in your mouth.[1]
  • Your gums bleed, look red or swollen, or feel tender, or your teeth feel loose. These can be signs of gum disease.[6]
  • Your mouth often feels dry.[4]

A dentist can often find the cause by smelling your breath and examining your mouth.[3] If your mouth turns out to be healthy, your dentist may suggest seeing your doctor, because conditions such as sinus problems, reflux or diabetes can also cause bad breath.[1] If a medicine seems to be drying out your mouth, ask your doctor or pharmacist about it rather than stopping it on your own.

Common questions

Does mouthwash get rid of bad breath?

It can help for a while. The ADA says over-the-counter mouthwashes can help kill bacteria or neutralize and temporarily mask bad breath. Research on mouthwash for bad breath is low certainty, so use it alongside brushing and cleaning between your teeth, not instead of them.[1, 2]

Should I clean my tongue?

Cleveland Clinic recommends it, because bacteria and food debris collect on the tongue. Trials of tongue cleaning are small and short, so the size of the benefit is uncertain, but it’s quick and cheap to add to your routine.[3, 2]

Can an oral probiotic help with bad breath?

Some strains have shown modest improvements in breath measures in studies, but results depend on the strain and dose, and the overall certainty of the evidence is limited. Think of a probiotic as an optional extra, not a replacement for brushing, cleaning between your teeth and dental visits.[7]

When is bad breath a sign of something else?

If it doesn’t go away with good brushing and flossing, or comes with a constant bad taste, bleeding or swollen gums, see a dentist. If your mouth is healthy, conditions such as sinus problems, reflux or diabetes can also cause bad breath, so your doctor may be the next step.[1, 6]

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Sources

  1. Bad breath. MouthHealthy, American Dental Association. www.mouthhealthy.org
  2. Kumbargere Nagraj S, et al. Interventions for managing halitosis. Cochrane Database of Systematic Reviews. 2019. pubmed.ncbi.nlm.nih.gov
  3. Bad breath (halitosis). Cleveland Clinic. Last reviewed August 5, 2025. my.clevelandclinic.org
  4. Dry mouth. National Institute of Dental and Craniofacial Research (NIH). Last reviewed October 2024. www.nidcr.nih.gov
  5. Brushing your teeth. MouthHealthy, American Dental Association. www.mouthhealthy.org
  6. Gum disease. MouthHealthy, American Dental Association. www.mouthhealthy.org
  7. Tang Z, Deng Y, Guo G, Zhou L. The effects of probiotics intervention on oral health outcomes: a comprehensive umbrella review of meta-analyses. Frontiers in Oral Health. 2026. www.frontiersin.org
  8. Wuri G, et al. Lactobacillus paracasei ET-22 and derived postbiotics reduce halitosis and modulate oral microbiome dysregulation: a randomized, double-blind placebo-controlled clinical trial. Food & Function. 2023. pubmed.ncbi.nlm.nih.gov

This guide is general information, not medical or dental advice. Talk to your dentist, doctor or pharmacist about your own health, especially if you take medication or have a health condition.