People with diabetes can have a fruity smell to their breath, Dr. Hirsch says. This can signal diabetic ketosis: When there isn’t enough of the hormone insulin or the body isn’t using it correctly, we start burning fat for fuel. This can lead to potentially fatal ketoacidosis if not caught and addressed early.
Infectious mononucleosis or mono strikes about 90 percent of the population worldwide; for some people, sour breath is among the first signs, Dr. Hirsch says.
Also known as fish-odour syndrome, trimethylaminuria is a rare metabolic disorder that occurs when a person can’t digest certain foods, including eggs, liver, legumes, fish, and some vegetables. As the foods sit undigested in the intestines, trimethylamine builds up and is expelled in bodily fluids like sweat and saliva, Dr. Hirsch explains. The smell is described as similar to rotting fish, urine, days-old garbage or rotten eggs. It’s not a life-threatening condition, but the unpleasant odour can lead to social isolation, depression and emotional disorders.