Crews called his three-part video series Dirty Little Secrets. It’s a frank account of his use of porn, which he says started when he was just 12 years old. The first instalment in his series has been viewed more than three million times, and has attracted thousands of comments.

Crews, a former American football player now better known for his TV and film roles, recounts in detail how he used to spend hours looking at porn.

“Pornography really messed up my life in a lot of ways,” he says. “If day turns into nights, and you are still watching, you’ve probably got a problem. And that was me.”

And he admits his addiction almost cost him his relationship with his wife, the gospel singer Rebecca King-Crews, from whom he temporarily separated. Thousands on Facebook applauded Crews for his honesty.

Others reacted by sharing their own experiences with sexual addiction. One user wrote: “I have wrestled for years – YEARS – with pornography. I am grateful today to say that I have a very specific sobriety date and I have stayed clean for some time now.”

However, the very idea of “porn addiction” is controversial. It’s not a disorder listed in the latest edition of Diagnostic and Statistical Manual, the “bible of psychiatry” issued by the American Psychiatric Association. Many experts say the brains of people watching porn don’t function in the same ways as the brains of, say, drug users, although the evidence is somewhat contradictory on this point. In one study, University of Cambridge researchers performed brain scans on 19 men watching porn, and the same reward centres of the brain were activated as when addicts see their drug of choice.

Nicole Prause, a researcher at the University of California Los Angeles, says that porn use shouldn’t be lumped in with drug and alcohol addiction.

“In the case of porn addictions, the brain looks similar to other addictions but only up to a point and then it diverges. When you look at porn, you get increases in learning and reward… but you don’t see some of the other hallmarks,” she told BBC Trending radio.

“In other addictions such as gambling, when you see a cue, for people who have a problem, the brain is more responsive. In the case of porn, with people who say they have problems, their responsiveness is decreased.”

Prause says the brain science means that porn is not addictive according to current models, and that treating it as an addiction can be counter-productive.

But calling porn non-addictive is no comfort to the thousands who talk about their struggles with pornography online. One such group on Reddit, r/NoFap (“fap” is slang for “masturbate”) has more than 170,000 followers, making it as popular as Reddit boards (aka subreddits) devoted to beer and Grand Theft Auto.

Many users of the forum – which is associated with a website of the same name – detail their intense struggles with their porn obsessions, and pledge not to use pornography or masturbate for a certain period of time. Tom (not his real name) is a teacher in the US Midwest. He told Trending that his obsession with porn began at a young age, and took a toll on his marriage.

“You’ve probably heard a saying that porn is great but it doesn’t compare to the real thing,” he says. “When you’re addicted to porn, you’ll feel the opposite. Sex is great, but it doesn’t compare to porn.”

At one point, Tom says, there were weeks when he spent hours every night looking at porn.

“I had trouble getting aroused with my wife, just because it wasn’t enough any more,” he says. Whatever scientists might say, Tom feels he’s addicted to porn – as do many others on the Reddit forum. He’s been trying to stop watching it for two years, and has gone as long as 90 days, but he says he still struggles to stop entirely.

By Dierdre Finnerty and Mike Wendling

First published by BBC