Hard lumps underneath the back of the ear may be related to the quality of the mastoid bone, or may be caused by enlarged lymph nodes behind the ear or sebaceous cysts. 1. Bone of the mastoid process: If there is a hard lump when pressed a little behind the ear after birth, and it is not accompanied by pain or discomfort, and it is found behind both ears, it is considered that it may be caused by the bone of the mastoid process. This is a normal physiological phenomenon and does not require special treatment. 2. Enlarged lymph nodes behind the ear: it is considered that it may be caused by tonsillitis, suppurative mumps, otitis media, etc. It is mainly caused by the infection invading the lymph nodes behind the ear, which leads to hard lumps under the back of the ear, and may be accompanied by tenderness and pain. 3. Sebaceous cysts: there are more hair follicles behind the ears, if you do not pay attention to the hygiene of the area for a long time, resulting in sebaceous gland blockage, resulting in secretions can not be discharged by the sebaceous gland ducts, and then form sebaceous gland cysts, which may lead to the back of the ear a little bit below the hard lumps when pressed, can be accompanied by pus, redness and swelling and other symptoms. If the symptoms are serious, it is recommended to consult a doctor as soon as possible to determine the cause of the disease and then give targeted treatment.