Phenol red is widely used as a pH indicator in various biological and chemical applications. In cell culture, it helps monitor the pH of the medium, turning yellow under acidic conditions and pink to red in alkaline environments. This allows researchers to assess cell health and metabolic activity. It is also employed in microbiology to detect pH changes in fermentation processes. Additionally, phenol red is used in urine analysis kits to identify pH levels, aiding in the diagnosis of certain medical conditions. In water quality testing, it serves as a tool to measure the pH of aquatic environments, ensuring suitable conditions for aquatic life.