2020 guidelines from Multinational Association of Supportive Care in Cancer and International Society for Oral Oncology (MASCC/ISOO):
Prevention with multi agent, combination oral care
Tooth brushing, flossing, mouthwashes (bland rinses, reduce bacterial build‐up) and applying moisturizing agents to the oral mucosal surfaces
benzydamine mouthwash for prevention
Topical morphine 0.2% mouthwash
Honey
Mucosal-protective agents(oral antacids, Gelcair, Orabase, Episil, topical kaolin/pectin) without any concrete evidence showing effectiveness
Saline and sodium bicarb rinses
No strong evidence but relatively harmless, expert opinion level of recommendation
Tooth brushing, flossing, mouthwashes (bland rinses, reduce bacterial build‐up) and applying moisturizing agents to the oral mucosal surfaces
No strong evidence but relatively harmless, expert opinion level of recommendation
Chewing gum was NOT effective in preventing oral<unk>  in pediatrics
Mucositis
Oral candidiasis
Myositis 
Herpes simplex virus infection
Dermatitis
Acute graft-versus-host disease
Alopecia
Conjunctivitis 