Pain in the left side of the jaw can be caused by trauma, gingivitis, periodontitis and other reasons. 1. Trauma: If a patient suffers from trauma, such as a violent collision or blow, it may cause damage to the left side of the jaw tissue and pain in the affected area. 2. Gingivitis: Gingivitis is an inflammation of the soft tissues around the teeth. If the patient does not pay attention to oral hygiene or suffers from bacterial or viral infections, the gum tissues will be stimulated by inflammation, and then pain will occur, so the patient may feel pain in the left side of the jaw. 3. Periodontitis: Periodontitis is mainly due to the stimulation of microorganisms and surrounding plaque, long-term damage to the tooth tissue, resulting in symptoms of tooth pain, and in serious cases, it may also cause jaw pain, lymph node enlargement and so on. It is recommended that patients can go to the hospital for a comprehensive examination, and according to the cause of the appropriate treatment.