"Some people go there because the intimacy in the relationship is as high as the person can stand it. If they were to unveil the sexual interest which is sort of their closely held secret, the intimacy would be way too high for their own ability to tolerate it, so they save it for elsewhere," Weston says.

Independent of the role it plays in relationships, people also look at pornography just to arouse themselves before or while masturbating.

"I think of porn addiction as a label that's used to put down behavior that's disapproved of socially," Violet Blue, a sex educator and author of The Ultimate Guide to Adult Videos, tells WebMD. "A lot of it is shaming masturbation."

Men are thought to be more easily aroused by erotic imagery than women are, but many women masturbate to pornography, too, she says.

She moderates an online message board for female enthusiasts called the Smart Girls' Porn Club. "I occasionally receive emails from members of the group about different kinds of sexual problems," she says, but none so far have expressed concerns about stopping.