Taste in the mouth may be caused by eating or drinking foods with bad odor, or by injury or inflammation in the mouth, or by systemic diseases that emit bad odor from the mouth. 1. Eating and drinking foods with bad taste: a bad taste in the mouth may be caused by eating and drinking foods with bad taste, such as seafood, fish and shrimp, durian, garlic and other foods with bad taste. 2. Oral injury or inflammation: when the oral cavity is traumatized or periodontitis, dental caries and other diseases, pathogenic bacteria multiply and easily produce flavored metabolites, in the oral cavity appear bloody taste or odor. 3. Systemic diseases: digestive diseases such as gastric ulcers or respiratory diseases such as bronchitis and other inflammatory diseases, due to the connection with the oral cavity, will also emit odor from the mouth. Mouth odor specific need to go to the hospital to check the oral cavity and systemic conditions, in order to determine the cause of the disease.