Oral mucositis is an inflammatory condition in the mouth. It is a frequent and unpleasant side effect of radiation and chemotherapy. The condition causes redness, mouth sores and ulcers that can be very painful, making it difficult to eat, drink and speak. Oral mucositis can lead to several problems, including nutritional deficiencies or hospitalization as a result of an inability to eat and an increased risk of infection due to open sores in the mouth. It can even interfere with your cancer treatment (Ref. 10, 11).