"Sex addiction" remains a controversial designation—often dismissed as a myth or providing talk-show punchlines thanks to high-profile [cases] such as … Tiger Woods. But compulsive sexual behavior … can systematically destroy a person's life much as addictions to alcohol or drugs can. And it's affecting an increasing number of Americans, say psychiatrists and addiction experts. "It's a national epidemic," says Steven Luff, coauthor of Pure Eyes: A Man's Guide to Sexual Integrity.

Reliable figures for the number of diagnosed sex addicts are difficult to come by, but the Society for the Advancement of Sexual Health, an education and sex-addiction treatment organization, estimates that between 3 and 5 percent of the U.S. population—or more than 9 million people—could meet the criteria for addiction. Some 1,500 sex therapists treating compulsive behavior are practicing today, up from fewer than 100 a decade ago, say several researchers and clinicians, while dozens of rehabilitation centers now advertise treatment programs, up from just five or six in the same period.

The demographics are changing, too. "Where it used to be 40- to 50-year-old men seeking treatment, now there are more females, adolescents, and senior citizens," says Tami VerHelst, vice president of the International Institute for Trauma and Addiction Professionals. "Grandfathers getting caught with porn on their computers by grandkids, and grandkids sexting at 12."