The causes of breath odor are oral diseases, digestive system diseases, diabetic ketoacidosis and other reasons. 1. Oral disease: not pay attention to oral hygiene, oral caries, periodontal abscess, dental plaque, etc. can appear oral odor. 2. Digestive system diseases: Helicobacter pylori infection, dyspepsia, gastric ulcer, duodenal ulcer and other digestive system diseases can also lead to oral odor. 3. Diabetic ketoacidosis: If you have a history of diabetes, do not standardize the use of hypoglycemic drugs, or you do not know that you have diabetes, has not been treated, resulting in diabetic ketoacidosis, there can be a rotten apple flavor of the breath, breathing deep and fast, nausea, vomiting and other symptoms. Breathing odor may also be caused by other diseases, such as sinusitis, organophosphorus poisoning, uremia, etc., the patient needs to consult a doctor in a timely manner, under the guidance of the doctor to cooperate with the treatment.