A composition for photodynamic therapy for treating Helicobacter pylori infections which contains methylene blue and has a pH of 7.6-9.5, a Helicobacter pylori infection treatment method, a system for sterilizing lesions caused by a Helicobacter pylori infection, and a method of operating the system for sterilizing lesions caused by a Helicobacter pylori infection are provided; also provided are a composition for photodynamic therapy for treating mucocutaneous infections which contains methylene blue and has a pH of 7.6-9.5, a mucocutaneous infection treatment method, a system for sterilizing lesions caused by a mucocutaneous infection, and a method of operating the system for sterilizing lesions caused by a mucocutaneous infection.