Bad breath is not always just a dental hygiene issue; it can be a hidden indicator of serious health problems. While often associated with poor oral care or food choices, recent research shows that certain breath odors may serve as warning signs for diseases like diabetes, kidney failure, or even cancer. Your breath carries chemical compounds reflecting what is happening inside your body, making it a potential diagnostic tool. Paying close attention to unusual or persistent odors, especially when accompanied by other symptoms, can help in early disease detection and improve long-term health outcomes.

Here are 9 health conditions that may cause bad breath:

While imaging and biopsies are standard for diagnosing lung cancer, new research suggests breath tests could offer a non-invasive and cost-effective alternative. One study used a device known as the “electronic nose” to detect volatile organic compounds (VOCs) associated with lung cancer, with promising results. The device accurately identified cancer in both smokers and non-smokers. As this technology evolves, breath analysis may become a tool for early lung cancer detection—long before symptoms appear.

Researchers found certain chemical markers in breath, such as acetone and pentane, can help diagnose heart failure. These compounds increase when the heart fails to pump blood efficiently and can be measured using mass spectrometry. Elevated levels have been linked to worse outcomes over time. If widely validated, breath tests could become an effective tool to monitor disease progression and treatment response.

People with poorly managed diabetes are prone to gum disease and dry mouth, both of which can cause bad breath. Particularly concerning is the presence of a fruity or acetone-like breath odor, which may indicate diabetic ketoacidosis (DKA), a potentially life-threatening complication. In DKA, the body breaks down fat for energy, releasing acidic ketones into the blood that can smell like nail polish remover. If you notice this odor along with symptoms like fatigue, nausea, or confusion, seek medical help immediately. Prompt treatment can prevent severe dehydration, organ failure, and coma, making early recognition of this distinctive smell critical for diabetics.

A fishy or ammonia-like breath odor may indicate kidney dysfunction. In kidney failure, the body cannot eliminate waste and toxins, leading to their buildup in the blood. These substances can be exhaled through the lungs, causing a foul smell known medically as “uremic fetor.” This symptom often appears in late-stage kidney disease and may be accompanied by fatigue, swelling, and changes in urination.

Morning bad breath is common, but if it is particularly strong and persistent, it may signal a sleep disorder such as sleep apnea. People with sleep apnea often breathe through their mouths at night due to airway obstruction, leading to dry mouth and increased bacterial growth. Mouth breathing reduces saliva’s natural cleansing effect, allowing odor-causing bacteria to thrive. If bad breath is accompanied by snoring or daytime sleepiness, a sleep study may be necessary.

Acid reflux and gastroesophageal reflux disease (GERD) can contribute to bad breath. When stomach acid backs up into the esophagus, it may carry partially digested food or intestinal gases, producing a sour or bitter odor. Dentists may also notice signs of reflux, such as enamel erosion or throat redness and inflammation. In some cases, Helicobacter pylori bacteria, which cause ulcers, have been linked to persistent bad breath.

Respiratory infections, allergies, and chronic sinusitis can cause bad breath by increasing mucus production. Postnasal drip allows mucus to accumulate at the back of the throat, where it can feed bacteria and cause odor. Nasal congestion may also force mouth breathing, worsening dry mouth and odor. If you experience frequent congestion and persistent bad breath, evaluation for sinus or allergy problems may be helpful.

Poor oral hygiene is the most common cause of bad breath. It can lead to gum disease (gingivitis), tooth decay, and infections, all of which cause foul odors. When bacteria break down food particles trapped in cavities or gum pockets, they release sulfur compounds with unpleasant smells. Therefore, brushing, flossing, and regular dental visits are essential not only for oral health but also for detecting more serious systemic problems that may first appear in the mouth.

Although rare, stomach cancer can also be detected through breath analysis. Researchers have developed breath analysis tools that identify compounds associated with stomach and esophageal cancers. One study showed this technology achieved 85% accuracy in distinguishing cancer patients from those with benign diseases. While more research is needed, breath tests may one day offer a safer, faster, and easier option for early cancer screening.