Oral mucositis, one of the most common complications of radiotherapy and chemotherapy for head and neck cancers, remains a therapeutic challenge. The pain resulting from erythema and deep ulcerations significantly reduces patients’ quality of life and makes oral food and fluid intake difficult. These effects may lead to malnutrition, dehydration, water-electrolyte imbalance, deterioration of treatment results, or even discontinuation of cancer therapy. The aim of this review is to present current epidemiology, main clinical features, treatment, and prevention recommendations of oral mucositis published by international oncological associations. Additionally, the paper emphasises available activities that may have a positive impact on the quality of life of palliative care patients.