Pain on the side of the ear when the mouth is open should be a problem with the temporomandibular joint. There are many reasons for this condition, sometimes it is a TMJ disorder caused by biting hard objects, or chewing on the side. It may also be TMJ pain caused by opening the mouth wide or yawning, so this is a time to eat soft foods and try not to open your mouth wide. If you have the bad habit of chewing on the side, you should actively correct it and insist on eating and chewing food evenly with both sides so that the muscles can be relaxed and the pain can be relieved. If you have the condition, it is recommended to go to a regular physical therapy department to do ultrashort wave, microwave and other physical therapy to promote blood circulation. Usually, when sleeping, keep lying flat, do not press the affected side, and keep the joint area warm when it is cold to avoid joint stiffness, which may aggravate the joint pain.