Phenol red solution is widely used as a pH indicator in biological and medical applications. It changes color depending on the acidity or alkalinity of the solution, making it ideal for monitoring pH in cell cultures and microbiological media. In tissue culture, it is commonly added to growth media to visually indicate pH shifts—turning yellow under acidic conditions and pink to red under basic conditions. It is also used in diagnostic procedures, such as the phenolsulfonphthalein test to assess kidney function, where the rate of excretion of the dye helps evaluate renal performance. Additionally, phenol red serves as an indicator in enzyme assays and colorimetric tests due to its reliable and reversible color transition in the physiologically relevant pH range.