1. Fruity breath: People with diabetes mellitus can have breath that smells like acetone. Diabetes mellitus is a chronic disease in which the blood sugar rises (hyperglycemia), either because the pancreas can’t make the insulin hormone or because the body can’t use insulin properly. And when the body can’t use glucose for energy, it breaks down fats. One of the byproducts of fat metabolism is ketones - which make the breath smell slightly sweet.3
2. Fetid, stinky breath: Syphilis — a sexually transmitted infection caused by Treponema pallidum bacteria — can make a patient’s breath smell really bad. The disease starts as a painless sore on the genitals, rectum or in the mouth. If it goes untreated, it can affect the heart, brain and other organs and even become life-threatening.
3. “Breath of a dead person”: Liver insufficiency or liver failure is a life-threatening situation in which the liver is unable to excrete bilirubin (waste material of liver) or filter blood or perform any of its functions. Technically, the odour from the mouth of a person who has liver failure is called “fetor hepaticus”, which translates as the breath of a dead person.
4. Sour or acidic breath: After the mouth, tummy and intestine problems are the most common reasons for bad breath. Gastroesophageal reflux disease, or GERD, is a condition in which the sphincter muscle at the lower end of the food pipe (oesophagus) is unable to close. The result: the stomach acid can flow back into the oesophagus. Yep, it’s as uncomfortable as it sounds and it can make the patient’s breath smell sour.
5. Fishy smell: Trimethylaminuria, also known as fish odour syndrome or fish malodor syndrome, is a rare metabolic disorder. Patients with this disorder can’t produce an enzyme called flavin-containing monooxygenase 3 (FMO3) which breaks down nitrogen-containing compounds from the diet, including trimethylamine. The result: breath that smells like fish.
6. Smells like ammonia, or pee: Kidney failure is a life-threatening condition in which the kidneys are no longer able to filter the blood - our kidneys absorb water and glucose before removing the waste products of digestion. People with kidney failure may have breath that smells like pee.
7. Burned sugar breath: Maple syrup urine disease is mainly seen in newborns - the patient’s body is unable to process certain protein-building blocks (amino acids). This makes their pee smell sweet and their breath smell like burned sugar. If not treated, this disease can be fatal.
8. Sweet and musty: Homocystinuria, a genetic disease in which the body can't process the amino acid methionine, can make the breath smell sweet and musty.
Homocystinuria typically affects infants and can be fatal if not treated.
9. Sweaty feet smell: Isovaleric acidemia is a genetic condition in which the enzyme responsible for the break down of the amino acid leucine stops working, which leads to the accumulation of isovaleric acid in the blood. This condition can be toxic and result in damage to the brain and nervous system. And it can also make the patient’s breath smell like sweaty feet.
10. Rotten meat smell: Bronchiectasis is a condition in which the airways of the lungs become widened, leading to a build-up of excess mucus. The resulting infection in the lungs can make the breath smell like rotten meat.
11. The odour of decay and putrefaction: Lung abscess — a microbial infection that can cause death (necrosis) of the lung tissue and accumulation of necrotic debris into deep cavities (more than 2 cm) — could be the reason a patient’s breath smells putrid.
12. Smells like old blood: Any disease or disorder related to the blood — example, bleeding disorders, coagulation disorders, and red blood cells disorder — can make a patient’s breath smell like blood or like a surgical wound that has just started healing.
13. Decaying wound smell: Liver cirrhosis is a chronic liver condition in which scar tissue forms in the liver - it may eventually lead to liver failure. People with this disorder can have breath that smells like a festering wound.