Phenol red (Phenolsulfonephthalein) is a pH indicator dye, relying on a distinct color change from pink to yellow in case of a positive reaction [2].In Vitro: Phenol red (PR) is the standard pH indicator in various cell and tissue culture media, as it provides a quick check for the health of the culture. Phenol red has also been used in multiple protocols to detect cellular hydrogen peroxide as well as peroxidase activity from human peroxidase enzymes.