Poor dental hygiene, eating particular foods, and smoking are just a few of the many causes of halitosis (bad breath). Yet sometimes, poor breath is an indication of something far more serious, like a life-threatening sickness. WebMD cites the following fatal conditions as potential sources of persistent bad breath, even after brushing:
Bad breath may result from a buildup of toxins in the body, which can occur with kidney illness. If the kidneys aren’t doing their job and getting rid of waste and toxins, they might build up in the mouth and give off a bad smell.