The right side of the neck tendon swelling is mainly caused by muscle tension and spasm of the sternocleidomastoid and trapezius muscles, and the main causes are cervical spondylosis, falling pillow, thyroid disease and lymphatic disease. 1. Cervical spondylosis: because of cervical disc herniation, cervical vertebrae physiological curvature straightening and other factors, leading to excessive pulling of sternocleidomastoid muscle, trapezius muscle and the surrounding soft tissues, resulting in muscle tension or even strain, thus resulting in neck distension and pain. 2. Falling pillow: because of improper sleeping posture or external force triggered by muscle injury, can also lead to neck pain. 3. Thyroid disease: such as hyperthyroidism, can cause thyroid enlargement, pulling the surrounding tissues to cause neck pain. 4. Lymphatic diseases: Due to the presence of more lymph nodes in the neck, when reactive lymphadenitis and other diseases occur, the lymph nodes become enlarged, which can also cause neck pain and discomfort. There are many reasons for the swelling of the right side of the neck, and it may also be related to lipoma and other diseases. If the symptoms continue to be unrelieved, it is recommended to consult a doctor in time to clarify the cause of the disease and carry out targeted treatment.