Sour gums may be caused by gum sensitivity, gum inflammation, dental caries and other reasons. 1. Gum sensitivity: teeth, especially the pulp tissue, in the external stimuli, such as temperature (cold, hot), chemicals (acid, sweet) and mechanical effects (friction or bite hard objects) caused by the soreness of the symptoms, once the stimulus to leave the symptom will disappear. 2. Inflammation of the gums: If the gums are localized with bacterial infection causing inflammation, or even periodontitis, soreness of the gums will occur. Periodontal inflammation should be controlled under the guidance of the doctor. 3. Dental caries: If the root caries develops to the middle caries and deep caries, it will involve the dentin, and there will be sensitivity and soreness of the teeth near the gums. The necrotic tissue should be removed in time for filling. There may also be other causes of sour gums, it is recommended to go to the dental specialist for diagnosis, to clarify the cause of the disease, and under the guidance of the doctor for treatment.