"I am often terrified about different aspects of characters I am playing. With respect to nudity, it was vital to the character in 'Shame', who wasn't supposed to be a very attractive character and needed to be emotionally naked and lost in different ways," Mulligan told thesun.co.uk.
"This is who she is - a character who can stand fully naked in front of her brother and not feel anything. But doing the nudity for 'Shame' was actually very liberating for me and it helped me deal with my own issues with my body," she added.
Mulligan, 27, says in her private life she is very "prudish" about her body.
"In my own life, I am very prudish about my body, or at least I have been in the past. I am always covering myself up rather than wearing skimpy outfits. I don't look good in very short skirts - at least I don't think so," she said.