Snapper Andrea Vecchiato invited the pair to be part of her project to raise funds for the National Autistic Society.
The actresses peeled off their clothes for the tasteful shots along with a line-up of models for the exhibition, which will run at The Gallery Soho in London.
Frost says, "I am deeply privileged to have been asked to be part of this great cause. I am thrilled to be in a position to help and will do anything I can to raise awareness for The National Autistic Society."
The exhibition, called The Sitter not the Artist, part 2, will run from 1-3 December (11).