Dr William Struthers, Associate Professor of Psychology at Wheaton College, said that 12 to 18-year-olds in the US and UK were "rampantly" accessing internet pornography.
"It's not a question of if my 10-year-old son is exposed. It's a matter of when," he said at a talk in the House of Commons yesterday.
Whereas 20 years ago, teenagers might have stumbled across the odd dirty magazine, the internet has made accessing pornography so easy that it is "intrusive".
It is not uncommon nowadays for teenagers - boys especially - to email sexually explicit material to each other and there are numerous websites offering inappropriate material with few restrictions to keep young people out.
And whereas previously, most girls viewed pornography as disgusting, they are becoming more and more open to it.
According to Dr Struthers, 67% of men and 49% of women see porn as an acceptable outlet for sexuality.
The fallout is a world in which young people are being "groomed into unhealthy attitudes to sex", he says.
Pornography is giving young people "unrealistic attitudes about sex and sexual relationships", he said, meaning that more girls are growing up with body image insecurity, while boys are experiencing "performance anxiety".
There is an increased belief that "porn is real life", he said, and that the way porn stars interact with each other is "applicable" in real life.
Dr Struthers explained that many young people were learning their sexual behaviour from pornography and that this was causing them to increasingly view sex as a "physical" rather than emotional act with real intimacy.
Sexual acts are "performances to be evaluated" and "men and women are props", he said.
"Pornography is teaching them that sex is available on demand, whenever, wherever and however they want it."
He added: "They are looking for intimacy and think that pornography is helping them [but it's] junk food."
When people feel they can't compare, their self-esteem falls, leaving them feeling even more withdrawn from others.
"Sex is about connecting with others," he said. "Pornography has co-opted this."
Dr Struthers warned that young people who frequently access pornography are less able to form healthy relationships with other people. They suffer from a "great inability to emotionally connect" and instead of experiencing genuine intimacy with a partner, settle for "very transient sexual rendezvous".
However, there are also concerns that consumption of pornography at too young an age will cause mental health problems later on in life.
"They are not ready for the stimulation that an adult brain can handle," said Dr Struther.
"They can see it, they know how to do it, but they don't know how to emotionally respond to the consequences of those actions."
He said parents needed to create an environment in which their kids could feel comfortable enough to tell them if they had seen something inappropriate.
He also expressed his support for opt-in filters to give parents the power to block porn coming into their homes via the internet.
Dr Struthers suggested that using such a filter would give parents the opportunity to explain the real value of sex and the appropriate place for it.
"[The effect of pornography] can be counteracted when you challenge those beliefs," he said.