A hard bag behind the ear may be the mastoid process, or it may be a symptom of certain diseases, such as mastoiditis, lymph node enlargement, etc., and you should consult a doctor in time to find out the cause of the disease. 1. Mastoid: the mastoid behind the ear, slightly higher than the surface of the skin, the surface of the mastoid if it is a bilateral symmetrical hard bag, the consideration is the mastoid itself bone, belongs to the normal anatomical structure and phenomenon. 2. Pathologic factors: (1) mastoiditis, mastoid is a bony structure located at the back of the earlobe, when the patient’s resistance is weak, the external pathogenic bacteria are strong or drainage is not smooth, resulting in the development of inflammation in the middle ear, spreading to the mastoid, causing mastoiditis. General ear symptoms include redness and swelling of the mastoid, ear pus, hearing loss, etc. Systemic symptoms such as fever, nausea and vomiting may also occur. (2) Inflammation of the throat, head and neck causes swelling of the lymph nodes behind the ear, which is also the inflammation of the local lymph nodes in the ear caused by inflammation. It is manifested as the size of the lymph nodes behind the ear exceeds the normal range, and the enlarged lymph nodes may become hard, which are usually movable and smooth to touch, with good movement all around. This symptom alone is not enough to diagnose the disease, it may also be caused by other factors, such as acne. Therefore, it is recommended to actively seek medical attention to clarify the cause of the disease and take standardized treatment.