In the film, the 45-year-old mother of two plays a high school teacher being terrorised at home and work by a much younger guy (Ryan Guzman) who is obsessed with her, reported E!Online.
Lopez said she never thought of using a body double as they needed things as close to real as possible.
"It was all me. And all Ryan, by the way... Those scenes are embarrassing. They are uncomfortable, but your job as an actress or an actor is to make it believable and this movie in particular... Hinges on if that was believable, that it was enough to make this guy go insane," she said.