In 1955, Marilyn Monroe created cinematic history when she stepped on a subway grate. A gust of air from the train below lifted the bombshell's billowy white dress, which she coquettishly tried to keep in place. Decades later, that iconic scene from "The Seven Year Itch" is still being recreated or acknowledged in a host of films and television programs.

That famous scene isn't the only legacy of the film. The theory behind the title -- that a married person gets the urge to cheat or leave the marriage after seven years -- has become an ubiquitous term in marital counseling, women's magazines and popular culture. Before 1952, however, when "The Seven Year Itch" premiered on Broadway, someone complaining of a seven-year itch probably had an uncomfortable skin disease like poison ivy or scabies, not a relationship problem.

Writer George Axelrod heard the term "seven-year itch" from a comedian who specialized in jokes about hillbillies, farm animals and ugly girls. Regarding one particular unsightly girl, the comedian claimed that he could tell she was over the age of 21 because she'd had the seven-year itch four times. Axelrod didn't think it was a particularly funny line -- he called it "hideous" to writer William Safire in 1992 -- but it was stuck in his head when he was searching for a title for his play about a man considering an affair while his wife was away [source: Safire]. Before Axelrod settled on that title, the main character had been married 10 years, not seven.

But seven had a better ring to it than 10, so Axelrod changed the script. The main character encounters the idea of the seven-year itch when he proofreads a book by a psychiatrist who claims that a high percentage of men stray during their seventh year of marriage. In other words, we have a fictional psychiatrist, an American playwright and a hillbilly comedian to thank for the idea of the seven-year itch. The question is, did they accidentally stumble on a real phenomenon? Or is the idea that men stray at seven years just a lot of hot air -- the kind that blew up Marilyn's skirt?