By Sean Nelson
Special to MSN Music

Though pop music seems to have changed a great deal over the past several decades, one phenomenon remains constant: the teen idol. From the swooning croon of early Sinatra through the apoplectic frenzy that greets British imports like One Direction (whose sophomore album, "Take Me Home," was released last week to record-shattering sales), teen idols have taken many forms, sported many fashions and covered many musical genres, all of which we examine in this gallery. In the end, however, whether boy band or solo heartthrob, the teen idol exists to generate two sounds: the screaming of kids in search of an outlet for their raging hormones and the ringing of cash registers.