The causes of pain in the left cheek may be the following: first, ulcers in the buccal mucosa, ulcers are often caused by eating spicy, irritating food, lack of vitamins and trace elements in the body, or teeth with relatively sharp tips, stub roots, stub crowns, which can often bite the buccal mucosa caused by local mucosal damage, the ulcerated surface will cause severe pain. The second, parotid duct mouth inflammation, the normal position of the parotid duct mouth is located in the mucosa corresponding to the buccal side of the second molar of the upper jaw, when normal is a soft small meat protrusion, is the opening of the parotid gland in the mouth, if the duct mouth is infected inflammation, or duct obstruction caused by the duct mouth inflammation, will also cause pain in the cheek when opening the mouth, there is this situation to go to the hospital for duct mouth unblocking and anti-inflammatory, to be able to relieve pain. The pain can only be relieved by going to the hospital for ductal opening and anti-inflammation.