For years in his teens, Daniel Simmons says he suffered “numerous breakdowns” — panic attacks and a series of unexplained physical problems. But in October 2013, at the age of 21, the intelligent and likeable, if slightly withdrawn, British music student underwent a miraculous change for the better.

“I suddenly had much more energy, and I could concentrate,” he says. “I was reading books for the first time in years. I was going out seeing my friends. I felt I had a sense of purpose.” By December, Simmons had resumed his studies at the University of York with a vigour he’d never felt before. His friends commented that Daniel seemed much happier. Privately, they wondered whether he was on anti-depressants. The truth was that Daniel had given up porn.

Simmons was 15 when he started looking at online pornography, relatively late by the standards of today’s youngsters. Last week the NSPCC released a report saying that children as young as ten are becoming addicted to online pornography, which can have a profound effect on the lives of its users, mentally, emotionally and physically. There is evidence to suggest that intensive use of internet porn gravely affects sexual function in the very young.

I can tell by Simmons’s voice that talking about his teens is painful. For six years of his life he felt “numbed”, and spent “two or three hours just watching porn, using multiple tabs. I’d call off sick and just watch it all day.” It was an unhappy, frightening time. “I was like a robot. I couldn’t relate to normal people.” His sexual tastes became synthetic and mutated in directions that frightened him, extending to rape- and transsexual pornography. More frightening still: “I couldn’t not watch it.” Holidays with his family were stressful, in case there was no internet. “Porn abstinence”, he says without hyperbole, saved his life.

Simmons stumbled across “porn abstinence”, a grassroots movement on the web, by accident when he typed “pornography” and “addiction” into his search engine. He read how thousands of men and boys were “rebooting” their brains off porn with the help of “porn recovery” sites. Unheard of three years ago, they are called things like Reboot Nation, Your Brain On Porn, QuitPornGetGirls, Fight The New Drug and the reddit site NoFap (fap is slang for masturbation). “I went 100 days without orgasm or masturbation, full-out ‘monk mode’ as it’s called in the community. I meditated daily. I was getting CBT [cognitive behavioural therapy]. I was going to the gym, I was writing, I just began to feel good.”

I had expected these websites to be boorish, but instead found the stories I read there often astonishing in many cases, thoughtfully articulated, worrying, and more often than not, written by young teenagers. Porn has wrecked their lives, you’ll read again and again on the forums. “I’m a loser piece of s*** who should die,” writes a teenager, aged 16. A 12-year-old says his preoccupation with hardcore pornography has crossed over to Facebook: “I post pictures online of these girls and get other people to Photoshop them nude. It’s disgusting and I know it is.”

Lekajones put it forcefully in a message he posted on NoFap last week: “I used to think porn was normal for guys to use and it was an acceptable substitution for sex used in moderation. NO! NO! NO! Porn is a parasite that will destroy, sabotage and hurt you.” Since they’ve started Your Brain On Porn’s “no-porn, no-masturbation” journey, they’re rediscovered their passion, ambition, capacity for love, joy and sex.

This month, Gary Wilson, a retired anatomy and physiology teacher who set up Your Brain On Porn, pushed the abstinence movement a step further into public consciousness by publishing Your Brain on Porn, a précis of his porn recovery website, which gets 20,000 unique new visitors a week. Wilson’s was the first such website on the net. “Evolution,” he says , “has not prepared your brain for today’s internet porn.”

Thousands of “rebooters”, including Simmons, credit Wilson’s website with changing their lives and emboldening them to take the very brave step of going public. “Our strength is in our numbers”, Simmons boldly tells viewers in a YouTube interview. “Our opponent [the porn industry] is a giant compared to us.”

A radio show host and vlogger on yourbrainrebalanced.com, he has also just made a documentary on porn’s damaging effects. “Porn is glorified as this great, fun activity. If you think of the tobacco wars, nobody could imagine that cigarettes could be so harmful.”

The real shocker for him — and this he had in common with many of the hundreds of thousands of young men who now form part of this anti-porn revolution — was the main physical consequence of giving up porn: “It might sound ridiculous that there’s a connection,” he says, “but I had my first erection in years.

“Porn makes you see other people as objects. I couldn’t talk to women and couldn’t feel interested in them. I had no libido. When I did go bed with them, I had erectile dysfunction, which was extremely embarrassing and disturbing. It’s like you’ve tuned your radio to a different frequency.”

A hundred days after he gave up pornography, he had his first wet dream. He told his friends and family about his problem with pornography. It helped. “I was actually very envious of my dad. They don’t know how good they had it, growing up before the internet and all this highly stimulating material.”

How worried is he about the new generation of teenagers? “Very. The younger you are, the more vulnerable you are. Anywhere where there is high speed, there are people suffering. It puts you in a stupor. It is extremely difficult to give up, and you need a lot of support. Young people [there are female porn addicts too] are losing years of their lives.”

I call Wilson in Ohio, where he lives. In his sixties, friendly and straight-talking, he comes from a generation of men whose porn use was mainly limited to magazines. People haven’t yet made the distinction, he says, between that and the never-ending supply of streamed hardcore material available now. This is not about sex addiction, Wilson says. It’s about endless novelty: the internet. “In the last two to three years,” Wilson tells me, “ they’ve finally done about six studies on erectile dysfunction.”

Those studies — conducted in Switzerland, Croatia, and Canada and by the US military — show that between 27 to 30 per cent of 16-to-21 year olds have been found to be suffering from ED. A study by the International Society For Sexual Medicine, published in 2013, found that one in four patients with newly diagnosed erectile dysfunction is under 40. “Now, the last real cross-sectional study was carried out before internet, in 1992,” Wilson says. “ED for men between the ages of 18 to 60 was around 5 per cent. We are looking at a 600 to 800 per cent rise.” He claims that men with “porn-induced ED” — which most doctors say doesn’t exist — “are taking two years or more to regain erectile function. Some guys are claiming they’re not recovering, they can’t get aroused.” There are a lot of under-18s turning to Viagra.

The accepted medical line on ED holds that its increase in young men correlates with rising obesity rates or alcohol consumption. But “fapstronauts” — men on the no-porn, no-masturbation challenge — don’t believe that. “We’ve only recently begun to see serious scientific studies on the effect of the internet on the brain,” says Wilson. What they seem to show is a correlation between porn use and depression, ED, anxiety, ADD, loss of interest in sex, falling grades and university dropout rates. “A teen’s brain is at its peak of dopamine production and neuroplasticity, highly vulnerable to addiction rewiring.” A study in the Journal of Early Adolescence this year shows that an increased use of internet pornography decreased boys’ academic performance six months later.

Wilson explains the science. The neurotransmitter dopamine’s evolutionary purpose, he says is to motivate you. “And dopamine surges for novelty.” The internet provides that but is subject to the law of diminishing returns. So the same erotic film loses its charge the more often it’s watched. “Internet porn is especially enticing to the reward circuit because novelty is only a click away,” Wilson says. Surprise, fear, disgust, anxiety — emotions you are likely to experience while roaming the borderless world of online porn — combines with arousal, “to give you a bigger brain chemical kick. What’s a brain to do when it has unlimited access to a super stimulating reward it was never evolved to handle? It adapts.” A Pavlovian super memory is formed. “Your tastes escalate, at the same time you become desensitised and feel numbed.”

Last year a Cambridge University study found the same brain changes in heavy internet porn users as in drug addicts. More than 50 per cent of subjects — their average age was 25 — had difficulty feeling aroused or getting erections with real partners. The brain science Wilson is talking about is the same as scientist Susan Greenfield was shot down for two years ago, when she warned about “Facebook zombies”. “And Susan was completely right.”

Recovering porn addicts have created their own vocabulary, with catchy slogans to go with them: “You’ve only f***ed yourself”, “Porn kills love”, “Get a new grip on life”. Their aim: to overcome “procrasturbation” by giving up PMO (porn masturbation orgasm) so that they can enjoy PIV (penis in vagina — sex with real women). At first “Fapstinence” is a void for these men. Wilson suggests installing monitoring apps on internet devices; diverting cravings into hobbies and getting out more: “Loneliness can trigger temptations.” Relapse is common and unpleasant. “Bad flu-like symptoms,” reports one young man. “My throat aches like crazy. Depressive. I see everything in black. It’s almost like the worst day of my life. Anxious, afraid. My voice is f-ed up.” But there are “NoFap Academies” you can join: “Sign up for NoFap’s Masturbation-Free April 2015 here!”

UnoroginalNam3 is 14 years old and 42 days into his NoFap challenge. “I’ve noticed a lot of things, including increased energy, confidence and reflexes/co-ordination. However what I did today trumped all of that. I talked to the girl I like, we had a good chat and I got her number. I will never go back to how I used to be. Never.” Others report improvements in their performance at work, memory, even the thickness of their hair and brightness of their eyes. Many say their voices are deeper. “I feel like I’m finally doing something worthy with my life,” writes Siroop. “Keep fighting this battle until porn and masturbation is completely irrelevant in my life! Stay strong, people.”

I ask Wilson where he thinks today’s teens are headed.

“You’ve got to wonder whether we’re going in the direction of Japan,” he says. A Japanese study found that 10 per cent of Japanese men have no interest in real sex because porn is easier and cheaper. “Is porn a factor in pregnancies going down? It’s killing young guys’ sexual performance. We hear guys say that they are scared because they have lost interest in sex — real relationships can’t compete with 300 pictures of vaginas a day.” Two boys in India contacted Wilson last week, terrified because they had found themselves logging on to child pornography sites. Others are disturbed by their synthetic and surreal new sexual tastes. “Tentacle porn is a big one,” Wilson says.

What’s tentacle porn? “Hentai porn. You’re not supposed to show penises and vaginas in Japan so they have monsters, things like giant octopuses, having sex with cartoon girls. That’s even more disturbing because it’s even further away from real life. But without porn they can’t get an erection. There are a lot of guys out there who are very frightened. Some are suicidal. They think they’re ruined for life.”

“I think a lot of men don’t understand what’s going on,” Simmons says. “Porn is seen as a normal thing, how can it be unhealthy?” Masturbation, young boys hear, is a healthy part of growing up: “good for your prostate”, it also supposedly stops you going bald. But young men don’t distinguish between masturbation and hardcore pornography.

“We’re a pair bonding species. We fall in love,” Wilson reminds all the teenage boys out there who have no idea what he is talking about. “When a man leaves porn behind, he realises that real partners are so much better than looking at pixels.”