Common reasons for bad urine odors include foods, vitamins and medicines, according to MedlinePlus. Asparagus, for example, is notorious for causing strong urine odors. Bacterial infections can also cause bad urine odors.
Another reason for bad urine odors is dehydration, says MedlinePlus. In this case, the concentrated urine smells like ammonia. Other causes are fistulas and infections in the bladder, liver failure and a condition called ketoniuria in which the urine has elevated levels of ketones and ketone bodies, according to MedicineNet. It can be a sign that diabetes is out of control or a complication of an eating disorder. The urine of a person with uncontrolled diabetes has a sweet odor, according to MedlinePlus.