Methylene blue is widely used in medical settings as a dye and treatment. It is employed in surgeries to help identify tissues, such as in parathyroid gland visualization, and as a stain in diagnostic procedures like Gram staining for bacteria. It also serves as an antidote for methemoglobinemia, a condition where blood cannot carry oxygen effectively. In microbiology, it is used to test for cell viability and respiration. Additionally, it has applications in aquaculture to treat fungal infections in fish and as a staining agent in histology to highlight cellular structures. In chemistry, it functions as a redox indicator in analytical procedures. Research is also exploring its potential in treating neurodegenerative diseases and as an antiviral agent.