There are numerous examples of this theme throughout the play. The protagonist, Chance Wayne, was once a high-school jock and drama star who thought he could make it big in the movies. But he failed, and instead he's ended up as a gigolo to an alcoholic, has-been film star called Alexandra Del Lago. He's desperately trying to recapture his youth while his soul and his looks decay.
Alexandra in turn also personifies the theme of decay. Once upon a time, she was a big Hollywood star, but she quit the movies when her looks started to fade, and since then has thrown herself into a self-destructive lifestyle of booze, drugs, and loveless sex.
Then there's Chance's high school sweetheart, Heavenly Finley. Her soul has been in decay ever since she slept with Chance and he gave her a sexually-transmitted disease (which led to physical decay). Just like Chance's youthful looks and popularity, and Alexandra's former stardom, Heavenly's virginity is something she'll never get back no matter how many times she puts on a white dress.