Watching natural-looking people engaging in sex that is consensual, pleasurable and realistic may not be harmful--heck, it might be a good idea--but that is generally not what the $97 billion global porn industry is shilling. Its producers have one goal: to get men off hard and fast for profit. That means eroticizing the degradation of women. In a study of behaviors in popular porn, nearly 90% of 304 random scenes contained physical aggression toward women, who nearly always responded neutrally or with pleasure. More insidiously, women would sometimes beg their partners to stop, then acquiesce and begin to enjoy the activity, regardless of how painful or debasing.

Over 40% of children ages 10 to 17 have been exposed to porn online, many accidentally. By college, according to a survey of more than 800 students titled " Generation XXX ," 90% of men and one-third of women had viewed porn during the preceding year. Even if what kids watch is utterly vanilla, they're still learning that women's sexuality exists for the benefit of men. An 11th-grade girl confided to me, "I watch porn because I'm a virgin and I want to figure out how sex works."

There is some indication that porn has a liberalizing effect: heterosexual male users are more likely than their peers to approve of same-sex marriage. On the other hand, they're less likely to support affirmative action for women. And porn users are also more likely than their peers to measure their masculinity, social status and self-worth by their ability to score with "hot" women.

Perhaps because it depicts aggression as sexy, porn also seems to desensitize: female porn users are less likely to intervene when seeing another woman being threatened or assaulted and are slower to recognize when they're in danger themselves. Boys, not surprisingly, use porn more than girls. Slightly under half of male college students use it weekly; only 3% of females do.

"Porn has terrible effects on what young women believe they are supposed to look like, particularly during sex," said Leslie Bell, a psychotherapist and author of Hard to Get.

"I'll be hooking up with some guy who's really hot," confided a high school senior in Northern California, "then things get heavier and all of a sudden my mind shifts and I'm not a real person: it's like, This is me performing. This is me acting ... And I don't even know who it is I'm playing, who that 'she' actually is. It's some fantasy girl, I guess, maybe the girl from porn."

For expert advice on talking to kids about porn, visit time.com/ideas

From the book GIRLS & SEX: Navigating the Complicated New Landscape by Peggy Orenstein. Copyright © 2016 by Peggy Orenstein. Reprinted by permission of Harper, an imprint of HarperCollins Publishers.