The reason for the left gum swelling and pain may be caused by oral inflammation, dental caries, oral tumor and other reasons. Oral inflammation: the left side of the gums swelling and pain can not be ruled out is gingivitis, periodontitis, wisdom teeth pericoronitis and other causes, oral inflammation occurs easily lead to inflammation of the gums and swelling and pain, can be localized rinsing on the medication, under the guidance of the doctor oral antibiotic medication for treatment, such as metronidazole tablets, amoxicillin and so on. When the inflammation is eliminated, periodontal treatment, removal of wisdom teeth. Dental caries: When teeth are decayed, bacteria erode the teeth and cause inflammation of the pulp, which can also cause swelling and pain in the gums. It is recommended to repair the caries as soon as possible, and after inducing pulpitis, it is necessary to repair the tooth after root canal treatment. Oral tumors: oral tumors around the gums or jawbone can also cause swollen and painful gums, it is recommended to go to the hospital for examination and then symptomatic treatment. No matter what the cause of swollen and painful gums, it is recommended to go to the hospital as soon as possible to check the cause of the disease, so as to achieve early detection and early treatment.