The causes of jaw swelling after radiotherapy for hypopharyngeal cancer include side effects of radiotherapy, complications of infection, or progression of hypopharyngeal cancer. 1. While killing cancer cells, radiation also has damaging effect on normal cells and tissues around cancer foci, thus resulting in congestion and edema of soft tissues in jaw area after injury. 2. After radiotherapy for hypopharyngeal cancer, the decrease of white blood cells and granulocytes will lead to secondary infection in the jaw area, which will not only cause localized swelling, but also pain, fever and other symptoms. 3. Due to the ineffectiveness of radiotherapy, metastasis of hypopharyngeal cancer occurs in the jaw area, which may also cause symptoms such as swelling and pain in the jaw. Once jaw swelling occurs after radiotherapy for hypopharyngeal cancer, it is recommended to consult a hospital as soon as possible for standardized diagnosis and treatment by professional doctors.