Sour mouth may be a sign of oral disease and GERD. 1. Oral diseases: Oral diseases, such as gingivitis and periodontitis, may cause bleeding in the mouth. Bleeding from the mouth may also be accompanied by a sour taste in the mouth and may be accompanied by a rusty odor. 2. Gastroesophageal Reflux Disease (GERD): GERD can be caused by impaired anti-reflux structures and functions, reduced esophageal clearance, and reduced resistance of the esophageal mucosa. Gastric acid refluxes into the esophagus, pharynx, and mouth, which can cause irritation of the local mucous membranes and lead to sourness of the mouth. It is recommended that patients go to the hospital as soon as possible, complete oral and other related tests and examinations to clarify the specific causes of acidity and receive treatment for the specific causes.