Common complaints are of food tasting too sweet or too bitter or of a continuous metallic taste. Complications
Sores or ulcerations can become infected by virus, bacteria or fungus. Pain and loss of taste perception makes it more difficult to eat, which leads to weight loss. Ulcers may act as a site for local infection and a portal of entry for oral flora that, in some instances, may cause septicaemia (especially in immunosuppressed patients). Therefore, oral mucositis can be a dose-limiting condition, disrupting a patient’s optimal cancer treatment plan and consequentially decreasing their chances of survival. Pathophysiology
The pathophysiology of mucositis is complex and multifactorial. Currently, Sonis five phase model is the accepted explanation for the process. The 5 stages are:

Initiation phase. Free radicals are produced due to DNA damage caused by chemo- or radiotherapy. Primary damage response. Chemotherapy, radiotherapy and free radicals all contribute to the activation of transcription factors, such as NF-κB. This results in the upregulation of pro-inflammatory cytokines, ceramide, nitric oxide and matrix metalloproteinases. The consequence of this is mucosal destruction, caused by thinning of the epithelium due to tissue injury and cell death. Signal amplification. Positive or negative feedback loops involving some of the molecules in the previous phase can exacerbate or prolong tissue injury. For example, the pro-inflammatory cytokine TNF-α can positively feedback on NF-κB thus inducing more pro-inflammatory cytokine production. Ulceration. Bacteria colonise ulcers and their cell wall products infiltrate the submucosa. This leads to activation of tissue macrophages, which causes further production of pro-inflammatory cytokines.
Mucositis is the painful inflammation and ulceration of the mucous membranes lining the digestive tract, usually as an adverse effect of  chemotherapy and radiotherapy treatment for cancer. Mucositis can occur anywhere along the gastrointestinal (GI) tract, but oral mucositis refers to the particular inflammation and ulceration that occurs in the mouth. Oral mucositis is a common and often debilitating complication of cancer treatment.Oral and gastrointestinal (GI) mucositis affects almost all patients undergoing high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT), 80% of patients with malignancies of the head and neck receiving radiotherapy, and a wide range of patients receiving chemotherapy. Alimentary tract mucositis increases mortality and morbidity and contributes to rising health care costs.For most cancer treatment, about 5–15% of patients get mucositis. However, with 5-fluorouracil (5-FU), up to 40% get mucositis, and 10–15% get grade 3–4 oral mucositis. Irinotecan is associated with severe GI mucositis in over 20% of patients. Seventy-five to eighty percent of bone marrow transplantation recipients experience mucositis, of which oral mucositis is the most common and most debilitating, especially when melphalan is used. In grade 3 oral mucositis, the patient is unable to eat solid food, and in grade 4, the patient is unable to consume liquids as well.Radiotherapy to the head and neck or to the pelvis or abdomen is associated with Grade 3 and Grade 4 oral or GI mucositis, respectively, often exceeding 50% of patients. Among patients undergoing head and neck radiotherapy, pain and decreased oral function may persist long after the conclusion of therapy.