There are many causes of blood in saliva that need to be alerted, such as pharyngeal diseases, oral diseases, digestive system diseases and so on. 1. Pharyngeal diseases: acute pharyngitis, acute laryngitis and other inflammatory diseases, can cause the mucous membrane of the throat congestion, edema, so the phenomenon of blood in the saliva may occur. 2. Oral diseases: oral ulcers, periodontitis, gingivitis, gingivoma and other diseases can also cause bleeding of the gums, oral mucosa and other locations, resulting in the phenomenon of blood in saliva. 3. Digestive system diseases: reflux esophagitis, gastritis, if the acute attack period, or the inflammation is more serious, may also cause the phenomenon of blood in the mouth. There are many reasons that lead to blood in the saliva, after the symptoms, it is recommended to go to the hospital in a timely manner to improve the examination, follow the doctor’s instructions to take standardized treatment, do not ignore the symptoms, take it lightly.