The actress, who plays prostitute Kelly-Marie Ball, told The Sun that she insisted on the wardrobe requirement.
Carman said: "It's pretty much in my contract. I have a three pairs rule. As long as I've got three on, I'm okay."
Of her sometimes kinky outfits in the show, she claimed: "I will put anything on, I really don't care."
Carman claimed that her character's heavy makeup means that she is not often recognised off camera, but added: "When I am it's always, 'Oh look, it's the prossie'. There's a fine line anyway with acting and prostitution!"
Shameless continues tonight at 10pm on Channel 4.