Why is beta-mercaptoethanol often added to cell culture media

Question

Many protocols suggest that beta-mercaptoethanol is necessary for growing cells. It is a reducing agent but what does it mechanistically do for your cells. When would one not add it.

Answer 1

2-me is a reducing agent necessary to be added to help keep free radical oxygen from affecting mouse cells. It is generally not necessary for human cells.

Also from S Bannai and Ishii et al., 2-mercaptoethanol improves tumor cell uptake of cystine by creating a reducing environment.