Hello, The bad smell may be due to the dental disease most commonly. Other causes are like: A cheesy smell usually indicates your bad breath has a nasal origin. A fruity smell may indicate uncontrolled diabetes due to increased. A fishy smell may indicate kidney disease, as increased urea levels can cause a fishy smell such as in (trimethylaminuria). An acidic smell can be a sign of asthma or cystic fibrosis. The scent of ammonia can indicate kidney problems. A sweet, musty odour may signal liver cirrhosis. A faecal odour may point to a bowel obstruction. Until examination is done it is difficult to say what it is. Get it examined for oral cavity, blood sugar, uric acid, ammonia levels or liver function tests. Please consult your physician he will examine and treat you accordingly. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Penchila Prasad Kandikattu , Internal Medicine Specialist