Unplanned radiation treatment breaks and prolongation of the radiation treatment time are associated with lower survival and locoregional control rates when radiotherapy or concurrent chemoradiotherapy is used in the curative treatment of head and neck cancer. Treatment of head and neck cancer is intense, involving high-dose, continuous radiotherapy, and often adding chemotherapy to radiotherapy. As the intensity of treatment regimens has escalated in recent years, clinical outcomes generally have improved. However, more intensive therapy also increases the incidence of treatment-related toxicities, particularly those impacting the mucosal lining of the oral cavity, pharynx, and cervical esophagus, and results in varying degrees of ulcerative mucositis. Ulcerative mucositis is a root cause of unscheduled radiation treatment breaks, which prolongs the total radiation treatment time. Alterations in radiotherapy and chemotherapy, including the use of continuous (i.e., 7 days/week) radiotherapy to ensure constant negative proliferative pressure, may improve efficacy outcomes. However, these approaches also increase the incidence of ulcerative mucositis, thereby increasing the incidence of unplanned radiation treatment breaks. Conversely, the reduction of ulcerative mucositis to minimize unplanned breaks in radiotherapy may enhance not only tolerability, but also efficacy outcomes. Several strategies to prevent ulcerative mucositis in radiotherapy for head and neck cancer have been evaluated, but none have demonstrated strong efficacy. Continued investigation is needed to identify superior radiation treatment regimens, technology, and supportive care that reduce unplanned radiation treatment breaks with the goal of improving clinical outcomes in head and neck cancer.