Halitosis (Bad Breath): Symptoms, Causes & Treatment Options

Gum disease is a prime environment for bad‑breath‑causing bacteria. Anaerobic bacteria, which grow in places with little to no oxygen, like gum pockets and the back of the tongue, produce foul-smelling compounds as they break down proteins. Poor oral health care, such as irregular brushing and flossing or skipped dental visits, allows plaque to build up along the gum line, irritating the gums and creating pockets where bacteria thrive. Gingivitis makes your gums red and swollen, and if it progresses to periodontitis the odours get stronger, and regular brushing won’t be enough.

You may also notice a metallic smell or taste in your mouth - this can occur when dental issues like gum disease or an infected tooth set up an overgrowth of bacteria, or when certain medications alter taste and saliva production.

Saliva naturally helps clean your mouth by washing away food particles and bacteria. If you don’t produce enough saliva, those odor-causing substances stick around. Dry mouth happens naturally while you sleep, which is why morning breath is so common. Medications, health conditions, or mouth breathing can also cause chronic dry mouth. 

GERD causes stomach acid to flow back into your throat and mouth, often resulting in a sour or acidic taste and smell that lingers, even with good oral hygiene. The acid can also damage your enamel, giving bacteria more places to grow and making bad breath worse over time.

Respiratory infections produce bacteria and mucus that smell. Sinus infections cause post-nasal drip, allowing infected mucus to slide down your throat. Pneumonia, bronchitis, and other lung infections can make your breath smell medicinal or metallic, and often require medical treatment.

Certain foods affect your breath by entering your bloodstream after digestion and being exhaled through your lungs. Garlic, onions, spicy dishes, cheese, pastrami, and certain spices contain strong-smelling compounds that can linger for hours. Drinks like orange juice, soda, and alcohol can also contribute by drying out your mouth, creating an environment where bacteria thrive. Sugary foods and drinks feed these bacteria, making bad breath even more likely. These foods not only affect your breath from within but also leave particles in your mouth that bacteria love, creating a double source of odour.

Uncontrolled diabetes can cause fruity or sweet-smelling breath, due to ketones in your blood. This happens when your body burns fat for energy instead of glucose. Diabetic ketoacidosis is a medical emergency. High blood sugar also encourages bacterial growth in your mouth, worsening breath.

Severely cutting calories puts your body into ketosis, so it burns stored fat and releases ketones. These can make your breath smell like acetone. Fasting also dries out your mouth, allowing bacteria to multiply. Together, the ketones and bacteria make breath especially noticeable.

Oral infections from tooth decay, abscesses, or surgical wounds create a breeding ground for bacteria. These infections often produce pus and dead tissue with a foul odor. Wisdom tooth extractions, root canals, and deep cavities are common culprits. A dentist is usually needed to treat them.

Tonsil stones form when food particles, dead cells, and bacteria collect in the tonsils. These white or yellow lumps, also known as calcium deposits, give off a strong sulfur smell. Many people don’t realize they have them, as they're often hidden, but they can cause persistent bad breath even with good oral care.

Smoking and chewing tobacco leave behind smelly chemicals and dry out your mouth, encouraging bacterial growth. Tobacco users are more prone to gum disease, and the combination of chemical residue and infection makes bad breath stick around.

Certain cancers can cause distinct breath odors as tumors break down tissue. The smell can be sweet, metallic, or resemble rotting flesh. Cancer treatments like chemotherapy and radiation can also dry out the mouth and affect taste. Early detection is critical.

Kidney disease can cause breath to smell like ammonia or urine as toxins build up. Advanced kidney failure may even create a fishy odor. Medical care is needed to address the underlying issue.

Liver disease can cause a sweet, musty smell known as fetor hepaticus. Medical care is needed to address the underlying issue.

Many medications dry out the mouth, giving bacteria a chance to flourish. Antihistamines, blood pressure drugs, and antidepressants are common offenders. Some medications also break down into chemicals that are released through your breath. Nitrates, certain chemotherapy drugs, and high-dose vitamins can all affect how your breath smells.

​​Dentures, bridges, and braces can trap food and bacteria in hard-to-clean spots, leading to odors. These devices need special care. Old fillings with gaps or rough edges also collect debris. Bacteria in the mouth can then metabolise this trapped material, producing and releasing foul-smelling compounds that cause bad breath. Regular dental visits help catch and fix these issues early.

Chronic sinusitis causes post-nasal drip that feeds bacteria in your throat. Nasal polyps and deviated septums can trap mucus and lead to infection. Throat conditions like strep or chronic tonsillitis can cause bacterial overgrowth. Even foreign objects in the nose - especially in kids - can produce strong, localized odors.

Stress can dry out your mouth and throw off your mouth’s bacterial balance. Hormonal changes during menstruation, pregnancy, or menopause can also affect your breath. Autoimmune disorders like Sjögren’s syndrome can nearly stop saliva production. Some people also become overly anxious about their breath, which can make the problem feel worse than it is.