The 24-year-old actress is playing Fiona Gallagher in the Showtime TV series, which has been adapted from the British programme of the same name.
Rossum has to take part in a number of raunchy bedroom scenes in the show and she's come up with a way to keep things private.
She said to Life & Style: 'I have this thing that I've invented with wardrobe and makeup that I like to call the 'vag pad'. It's a strip of rubbery stuff that gets adhered to me.'
Her co-star Justin Chatwin was asked what he uses to cover up and he said: 'When we were shooting the pilot, I remember coming out wearing nothing but a sock on my pecker.'