A hard lump on the right side of the neck may be caused by lymphadenitis, sebaceous cysts and thyroid cancer. 1. Lymphadenitis: usually caused by pathogenic bacterial infection, when the infection is serious, it will lead to bilateral or one-sided lymph node enlargement in the neck, manifested as hard lumps, which may be accompanied by symptoms such as redness, fever, pain, and so on. 2. Sebaceous cysts: staying up late for a long time or having an irregular diet may lead to more secretion of sebaceous glands and blockage of sebaceous gland ducts, causing sebaceous cysts, which often occur on the scalp, back of the neck, and chest where sebaceous glands secrete abundantly, and may be accompanied by pain, itching and other symptoms. 3. Thyroid tumor: it may be related to genetic factors, radiation and other factors, which may cause lumps on one side or both sides of the neck, with hard texture, and in serious cases, it may also make the patient suffer from dyspnea, hoarseness, swallowing disorders and other symptoms. There is a hard lump on the right side of the neck, which may also be caused by congenital diseases, etc. It is recommended to seek medical examination and treatment as soon as possible to avoid delays.