Mucositis is an inflammatory process that affects the mucous membranes of the oral cavity and gastrointestinal tract. ONS PEP resources focus on oral mucositis, which is estimated to occur in about 40% of patients secondary to chemotherapy and almost 100% of those receiving radiation for head and neck cancer. Approximately 80% of those undergoing hematopoietic stem cell transplantation will experience some level of oral mucositis. Oral mucositis can range in degree from mild changes in sensation to severe oral pain, infection, and ulcerative bleeding lesions.