There are several reasons why patients have a condition of a hard bag behind the back of the ear: 1. Sebaceous cysts: often occur as a result of localized skin sebaceous cysts behind the back of the ear, mainly related to local skin uncleanliness factors, which often cause patients to have blocked skin follicles and form localized cysts that bulge. Some patients may also develop further secondary infections, resulting in cysts with symptoms of congestion, swelling and pain, often requiring further anti-infective treatment. If the hard pack is large and causes obvious discomfort, further surgical treatment measures can be taken. 2. Inflammatory infections: Some patients may also develop swollen lymph nodes, often related to inflammatory infections of the surrounding skin and respiratory tract. 3. Malignant neoplastic diseases: Some patients may also develop painless lymph node enlargement, which may be related to malignant neoplasms of the nasal cavity, sinuses, nasopharynx and throat. Malignant neoplastic diseases in the nasal cavity, sinuses, nasopharynx and pharynx may be related, and further detailed examination is needed if necessary.