What is the effect of phenol red in DMEM (Dulbecco’s Modified Eagle Medium)?

While serving primarily as a pH indicator in cell culture, phenol red is seen to have estrogenic effects, due to similarity in structure to nonsteroidal estrogens, and the ability to promote cell proliferation in some cell lines. Thus, if working with cells that are responsive to estrogen, you may want to take into consideration the estrogenic effects or use a formulation of DMEM without phenol red.