Phenol red pH indicator solution is widely used to monitor pH changes in cell culture and biological systems. It is commonly added to cell culture media to visually indicate the acidity or alkalinity of the environment. In neutral solutions, it appears red, turns yellow under acidic conditions, and becomes pink to purple in alkaline conditions. This color change helps researchers quickly assess the health of cell cultures without needing complex instruments. It is especially useful in tissue culture labs and during incubation processes where pH stability is critical. Phenol red is also used in water quality testing and educational experiments to demonstrate pH effects in liquids.