Teenage boys watch pornography. Estimates, based on the research evidence that I have tracked, suggest that about half of all pre-teens and teenagers between the ages of 11 and 16 watch pornography. About 3 in 10 boys age 11 and 12 watch pornography and by the age of 18, the figure jumps to about 9 in 10 boys that have watched, or do watch, pornography. The average age at which boys are first exposed to pornography is estimated to be 11 years, but there is research evidence that boys as young as eight years old view pornography.

Pornhub is one of the largest and most popular pornography websites and they occasionally release statistics about the usage on their site. In 2016, 92 billion (yes, billion) videos were clicked on to on Pornhub. That equated to 4.5 billion hours of porn that was streamed. That's just one porn website. Estimates suggest that porn sites attract more visitors each month than Amazon, Netflix and Twitter combined.

So, if you are the parent of a teenage boy, you need to sit up and take notice. Whatever attempts you have made to educate your son about sex and relationships probably pales into insignificance compared to the way pornography will have educated them.

Because of the way pornography affects a teenager's brain, it is very easy for them to become rapidly addicted. Young teenagers have a very natural and instinctive inquisitiveness about sex. They are biologically programmed to find out about sex and the internet now provides the most simple access for them to information. If they Google the word "sex" they will be instantly brought to millions of pornographic images, almost all of which will then link them to a pornography site.

But, returning to the plasticity and development of a teenager's brain. We know that the brain's reward centre will be stimulated by pornography. The reward centre in a teenager's brain will respond twice as powerfully than that of an adult. In essence, watching pornography gives a teenage boy a chemical hit of pleasure, with the release of dopamine, and that dopamine high will also create a craving for the release of more dopamine. Over time, however, excessive levels of dopamine cause a teenager's brain to develop tolerance and so they need either more porn, novel porn or more extreme porn, to be able to achieve the same pleasure response.

Researchers have established that regularly watching pornography leads inevitably to teens becoming accustomed to the porn they have already seen, and moving on to more extreme forms of pornography to get aroused. This, in turn changes their "tastes" (in terms of sex) and disrupts their ability to have regular relationships with peers. Youngsters can become desensitised to things that they previously may have considered disgusting, degrading or dangerous, such that extreme sex acts can appear to be more normal, acceptable and common to them. About 90pc of online pornography contains violence, and that violence is primarily towards women.

Unsurprisingly, research has also clearly shown that watching pornography will affect teenage boys' attitudes and beliefs towards sex, women and relationships. Pornography becomes the teacher, and frighteningly, the moral compass, for boys' sexual behaviour. There was a study done in 2015 that aggregated evidence from 22 studies across the world and concluded that "the accumulated data leave little doubt that, on the average, individuals who consume pornography more frequently are more likely to hold attitudes conducive to sexual aggression and engage in actual acts of sexual aggression than individuals who do not consume pornography or who consume pornography less frequently."

When teenagers rely on pornography to learn about sex, they usually expect any sexual partner to act out what they've seen, even if it's degrading, painful or dangerous.

Over time, teenage boys who continue to consume pornography will become increasingly less satisfied with any real life relationships that they manage to have, as pornography will affect their ability to be attracted to others, to become sexually aroused by another person, will reduce their sex drive and may even lead to erectile dysfunction and difficulty reaching orgasm.

Are you frightened yet? Hopefully I haven't terrified you to the point that you can't bear to read more, because, for all the harm that pornography is causing, we also have to accept that it isn't going away. We, as parents, can't simply adopt a "head in the sand" approach to it. We need to address it as a very real, very significant and very dangerous issue in teenage boys' lives.

So, what can we do?

In the first instance we need to educate ourselves. I've summarised some of the research evidence above, but there is a lot more to it than I have even been able to collate in the space I have here. I'd recommend a website called "Fight the New Drug" as an excellent resource about the harmful effects of pornography. We need that information if we are to challenge the attitudes and beliefs that our sons may develop when they start watching pornography.

Much like we need to promote an abstinence message in relation to alcohol to preteens and younger teens, we must do the same with pornography. We must monitor our children's use of devices and make it hard to access inappropriate material. Use things like digital parental controls on any device that your child may use to access to the internet. We need to let younger children know that we disapprove of pornography for all the good reasons we will have established from our self-education on the topic.

Pornography will not be addressed in school sex education programmes, just like they don't deal with masturbation. Even if schools do deal with the topic, you can't rely on a school teacher to share your values, beliefs and attitudes. Nor can you rely on the discussions about pornography happening in time to give your son some hope of being able to contextualise and question what he will see. Sex education, and education about pornography is your job with your son. It is not something that can be sub-contracted out to schools or the internet.

This will mean that we have to start talking about sex, sexuality and relationships with our sons, probably from the age of 9 or 10 onwards. And it isn't simply giving them "the talk". It is an ongoing process of engagement with them about our attitudes and beliefs about sex and relationships. We need to educate them about how pornography is not representative of real relationships. We need to use every opportunity to talk about sex, relationships, morals and our values and give our sons a context for critically evaluating what they will see. There's a documentary series on Channel 4 at the moment called Let's Talk About Sex, which looks at how sex education has changed over the decades. It proved to be the perfect chance for me to reopen discussions with my own 14-year-old son because the programme combined humour and realism, allowing him and me to stay watching and chatting without either of us squirming away in embarrassment.

We need to accept that there will come a time when our sons will view pornography and so we need to make sure that we - and they - are prepared for all that it might bring to their understanding about sex and relationships.

David Coleman is a clinical psychologist and is an adjunct associate professor at the School of Psychology, UCD

Irish Independent