Methylene blue is widely used in medical settings as a diagnostic tool and treatment. It is employed in surgeries to help identify certain tissues and structures, such as parathyroid glands, due to its staining properties. Additionally, it is used as a treatment for methemoglobinemia, a condition where blood cannot carry oxygen effectively, by converting methemoglobin back to hemoglobin. In microbiology, it serves as a stain to enhance the visibility of microorganisms under a microscope. It is also utilized in aquaculture to treat fungal infections in fish and their eggs. Furthermore, methylene blue has applications in chemistry as a redox indicator in titration experiments.