In the 1955 Billy Wilder film "The Seven Year Itch," The Girl (Marilyn Monroe) and her neighbor Richard Sherman (Tom Ewell) take a stroll in NYC. As she walks over a subway grate, a train passes below, blowing her skirt up, sparking Sherman's fantasies.

He's been married for seven years, and his urge to stray is dubbed "the seven-year itch." The film is a comedy, so (spoiler alert) no harm, no foul. But if you're one of the 25 percent of American adults who've had to deal with a persistent itch, called pruritus, you know it's nothing to laugh at.

Scratching the Surface: Pruritus can alert you to severely dry and aging skin, an allergy (dermatitis) or troublesome immune response (psoriasis), certain cancers and even kidney problems. That's why it's important to ID the cause.

-For dermatitis and psoriasis, try antihistamines, UV light therapy and/or topical compounds such as corticosteroid ointments; for dry skin, avoid harsh soaps and use lotions regularly.

-If it's kidney-disease-related, gabapentin and pregabalin (used to treat epilepsy and neuropathic pain) may help. Also, talk to your doc about foods to avoid.

-Cancer-related itching may result from infection or jaundice, or the tumors themselves. It can be treated with antihistamines, steroids, antidepressants and alternative, stress-reduction therapies.

Breaking News: There may be a way to turn off the itch sensation altogether! Chinese scientists isolated itch-processing neurons in the spinal cord and, in the lab, have been able to interrupt the pathway that triggers "itch-induced scratching behavior." Targeted therapy is under development.