A hard lump on the neck below the ear may be caused by enlarged lymph nodes, sebaceous cysts and other reasons. 1. Enlarged lymph nodes: mostly due to infections of neighboring tissues and organs, such as tonsillitis, chronic otitis media, etc., which may lead to enlarged lymph nodes in the neck below the ear, resulting in a hard lump in the neck below the ear, which may be accompanied by obvious tenderness, or nasopharyngeal carcinoma and other malignant tumors leading to enlarged and metastasized lymph nodes in the local lymph nodes, which are fixed and inactive, with no obvious tenderness. 2. Sebaceous cyst: usually due to the blockage of sebaceous gland opening in the skin of neck below the ear, the sebaceous gland secretion can not be discharged in time, and over a long period of time, it is easy to be retained in the local area to form sebaceous cyst, which causes a hard lump in the neck below the ear. Infection can lead to redness, swelling and pain in the affected area of the skin. A hard lump on the neck below the ear may also be caused by other reasons, and should be consulted as soon as possible to clarify the diagnosis and give targeted treatment.