There are several systemic diseases that can cause halitosis (bad breath). They are: chronic liver failure, bronchial or other lung infections, renal failure, carcinoma, trimethylaminuria, diabetes mellitus and metabolic dysfunction. Halitosis from these types of diseases is not originating from the oral cavity. Halitosis stemming from systemic diseases is extremely infrequent in the general population and most cases of halitosis will conclude with the source being from the oral cavity.

Chronic Liver Failure - Fetor hepaticus is chronic bad breath due to liver failure. It is also known as the "breath of the dead". It is a late sign of liver failure.

Bronchial or Other Lung Infections - Other types of infections may include: lung abscess, acute bronchitis and emphysema.

Renal Failure - diseases such as diabetes mellitus may include renal failure as a consequence of the disease progression.

Carcinoma - this is any cancer that arises from epithelial cells and invades surrounding tissues and organs.

Trimethylaminuria - "fish odor syndrome", is a rare genetic disease. The individual who has this disease is unable to properly breakdown trimethylamine that is consumed in their diet. When it is not properly broken down it builds up and is then released in the individual's sweat, urine and breath. The breath as well as the sweat and urine give off a strong fishy odor.

Diabetes Mellitus - This is a syndrome that is characterized by disordered metabolism, uncontrolled blood sugar levels, excessive urine production, thirst, and also blurred vision. One consequence of diabetes mellitus is diabetic nephropathy (requiring renal dialysis) and can lead to renal failure, which can cause bad breath.

Metabolic Dysfunction - Metabolism involves the breaking down of complex organic components of the body, generating a release of energy, which is erquired for other bodily processes. Metabolic dysfunction is when this process is disrupted by disease and is present in many systemic diseases.

Bad breath is most likely an insignificant part of diagnosing these systemic diseases so someone who is experiencing bad breath should not jump to the conclusion that they may have one of these diseases.

Misc. - Bad breath when it comes to systemic diseases is more of a consequence than a diagnosing symptom. Usually the diagnosis is already made by the time bad breath enters the equation. Like in liver failure, the bad breath usually comes at the final stages of the disease, when the disease itself is pretty obvious.

Systemic diseases are diseases that involve many organs or they involve the entire body.