Blood in saliva may be caused by periodontal disease, throat disease, digestive system disease, etc., which need to be clearly diagnosed through periodontal examination, laryngoscopy, gastroscopy, etc., as follows. 1. Periodontal disease: gingivitis can cause gums to bleed after being stimulated, periodontitis can cause spontaneous bleeding of periodontal tissues, all of which can lead to blood in saliva, and need to be clearly diagnosed through periodontal examination. 2. Diseases of the pharynx: pharyngitis may lead to bleeding in the throat, which requires laryngoscopy to make a clear diagnosis. 3. Digestive system diseases: reflux esophagitis, duodenal ulcer, etc. may lead to bleeding, and blood may reflux into the mouth, making blood in saliva, which needs to be clearly diagnosed through gastroscopy. There may be other reasons for blood in the saliva, it is recommended to go to the hospital in time, with the help of the doctor to clarify the cause of the disease for targeted treatment.