A top psychosexual therapist is warning about a surge in the number of young men suffering sexual health problems because of online pornography.
Angela Gregory says more and more men in their late teens and early 20s are suffering from erectile dysfunction.
She puts the blame on people becoming addicted to watching online porn.
There are no official figures but she says a lot of the time it is via smartphones and laptops.
"What I've seen over the last 16 years, particularly the last five years, is an increase in the amount of younger men being referred," she said.
"Our experience is that historically men that were referred to our clinic with problems with erectile dysfunction were older men whose issues were related to diabetes, MS, cardio vascular disease.
"These younger men do not have organic disease, they've already been tested by their GP and everything is fine.
"So one of the first assessment questions I'd always ask now is about pornography and masturbatory habit because that can be the cause of their issues about maintaining an erection with a partner."
Nick, not his real name, started watching porn when he got his first laptop aged 15.
"It quickly escalated and it was every day. What I was watching, it definitely got more extreme over a short period of time in my case.
"There was nothing that would give me a kick. Normal stuff didn't do anything any more, so I had to get more and more extreme material.
"[It was] disturbing stuff that disturbed me that, in normal life, I wouldn't dream of doing."
It wasn't long before Nick's own sexual health began to suffer.
'Wired to porn'
"I found that when I was lying next to a girl a lot that I just wouldn't be horny at all, despite being really attracted to the girl and wanting to have sex with her, [because] my sexuality was completely wired towards porn.
"At my peak I was probably watching up to two hours of porn every day."
Newsbeat has been finding out how having easy access to online porn is affecting body image, sex and relationships for documentary Brought up on Porn, available now on iPlayer.
Once Nick realised he had a problem he tried to get help.
"At first I went to a doctor and she said, 'I don't think there's enough evidence to suggest it's a thing, however I do have a lot of young men coming to me with this problem.'"
In the end Nick went 100 days without watching porn and was relieved when things got back to normal.
"My libido came back with a vengeance and I met this girl and it was great.
"For the first time in ages I was able to flirt and within quite a short time I was able to have normal sex.
"I was feeling so balanced and happy."
He also has advice for anyone suffering with a similar problem.
"Once I recovered I spent a lot of time on online forums trying to help others do the same.
"There's a lot more information online than when I had problems.
"You should tell your friends, tell people who are close to you or just a couple of people you trust. And don't worry, there are many of us in the same boat."
If you think you're having a problem related to porn, Angela Gregory advises talking to your GP.
Help is also available at BBC Advice or at organisations like the College of Sexual and Relationship Therapists and the Association for the Treatment of Sexual Addiction and Compulsivity.
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