It was an ordinary weekday morning when Caroline first noticed how much pornography was taking over her life. With 15 minutes to go before she was due to leave for a job interview, she opened up her laptop to print off an extra copy of her CV and there, onscreen, was a grab she'd saved from pornhub.com.

"I remember the feeling of being sucked in, really wanting that two-minute fix, that numbness I got when I used porn," says Caroline. "I was stressed out, and I risked being late for my interview, but I pressed play anyway and fast-forwarded it to the bit I wanted. It took two minutes." But the relief was to be short-lived. "Afterwards I just hated myself for giving in and getting off on images that treated women like pieces of meat. But I kept going back."

Although there is much debate about whether "porn addiction" even exists, Caroline, a 21-year-old English graduate, has just finished seeing a sex addiction therapist to help get her porn habit under control. Having started watching porn out of curiosity when it became available over the internet in her mid-teens, she and her mates used it as a graphic form of sex education. She saw nothing wrong with it, particularly as she was raised in a generation of girls for whom it was seen as hip and liberated to enjoy watching sex.

Then, as she entered a depressed job market after university, it became a form of escape, a default she turned to whenever she felt anxious or bored. "I'd be stuck at home in front of my laptop on my own all day. I'd wake up with all these ideas for the day – and end up surfing for porn, trying to distract myself, eating and then going back for more porn. No one would ever have known. But I didn't get much done. It was like a constant battle between my sexual urges and my self-control. I'd think to myself: 'It's not doing any harm.' But then I started to loathe myself for giving in and wasting so much time on it."

Caroline is not alone. While it's accepted that women are watching – and enjoying – porn more and more, it's less recognised that some are also finding it hard to stop. At Quit Porn Addiction, the UK's main porn counselling service, almost one in three clients are women struggling with their own porn use, says founder and counsellor Jason Dean. Two years ago, there were none.While more than six out of 10 women say they view web porn, one study in 2006 by the Internet Filter Review found that 17% of women describe themselves as "addicted".

Dean says: "I remember getting my first woman contacts about two years ago and thinking that was fairly unusual. Now I'm hearing from about 70 women a year who are coming for their own reasons, not because their male partners have a problem."

There is little difference in the way the genders become hooked, says Jason. There is the same pattern of exposure, addiction, and desensitisation to increasingly hardcore images. The main contrast between male and female porn addicts is how much more guilty women feel. "Porn addiction is seen as a man's problem – and therefore not acceptable for women," says Dean. "There's a real sense among women that it's bad, dirty, wrong and they're often unable to get beyond that."

Orgasm releases a dopamine-oxytocin high that has been compared to a heroin hit, and many regular users of internet porn report experiencing an almost trance-like effect that not only makes them feel oblivious to the world, but also gives them a sense of power that they don't have in real life. "The PC becomes an erogenous zone. The more you keep trying to put porn out of your mind, the more it keeps popping back in. The brain then learns that porn is the only way to cope with anxiety."

Yet, what strikes you on the porn addiction websites is the real sense of despair and loneliness for the women who get caught up in it – and how early it starts. Many talk of a problem dating back to their early teens, before they've even had a relationship.

One 19-year-old college student writes: "It started seriously when I was about 14, I stumbled across some pictures while doing homework. Because all I had typed into Google was 'cream and sugar', I knew my parents wouldn't notice. I learnt all the ways round the parental controls, meticulously deleted my activities on the history and deleted the search engine entries every time."

Psychotherapist Phillip Hodson, of the British Association of Counselling and Psychotherapy, says that in consulting rooms, the issue of woman habitually using porn "is something that has not been aired before. It's something new that's just beginning to surface . . . Traditionally women's voices have been against porn. It's seen as more of a male thing, because it's men who are supposed to be visually stimulated. But that doesn't mean that women aren't. Men are just maybe more so."

Women who become regular users can suffer depression and low self-esteem because it can be hard to reconcile their enjoyment of porn with their intellectual dislike of seeing women used as sex objects. "Porn has an instant effect on the human body and mind and the psyche, even if you disapprove of what you are seeing . . . So women may find their body is saying yes, even though their mind may be saying no – and that can be upsetting."

But as porn becomes more pervasive, Hodson observes that women are now also using it as a quick way to have sex without emotional investment, just as men traditionally have. "For women, just as for men, the internet is able to satisfy that need in rather a raw, crude sense, quickly and easily. Why serenade someone and go through all the courtship rituals with another person when you have Google?"

But it's important not to turn lone use of porn into a catastrophe, adds Hodson. For many women, it's a phase that will pass – either because they take stock, they realise it's becoming a problem, it becomes boring – or their life fills up again with better alternatives.

"I have a problem with the word addiction," he says. "Sex is a very natural function – and what is an abnormal level of sex to have or to want? If a woman is taking two minutes to orgasm to porn, and she's doing it, say, 10 times a day, that's still only 20 minutes a day.

"But if porn does become a habit that interferes in other areas, it might be an opportunity to take stock and realise there's not enough happening in your life. Forgive yourself for being tempted and having a few orgasms. If it goes beyond that, there are people outside who can help."

The first support group in the US run for women by women was founded by Crystal Renaud, who also wrote a new book on women's addiction to porn, called Dirty Girls Come Clean.

A committed Christian, she first came across porn at the age of 11 in a magazine that belonged to her brother, and was addicted for eight years before she got her wake-up call when she arranged an anonymous hook-up with a man she met over the net. Renaud recalls: "I had no friends. No passions. I had one mission and purpose in my life: pornography. Any way I could find it, I would. It didn't matter where I was or what I was doing. Home, school, my friend's houses, summer camp and yes, even church: my addiction came too.

"Porn. Masturbation. Cybersex. Webcam sex. Phone sex. Anything you could think up, I watched, experienced and enjoyed. No matter how many times I said I would stop, I would just keep doing it."

As a trained counsellor, Renaud now calls women's addiction to pornography "widespread and silent". In almost every case, the women she meets believe they are the only ones ever to have struggled with the issue. "Porn and sexual addiction has always been referred to as a man's problem," says Renaud. "But for women it's an unspoken struggle. We have to give them the opportunity to say: 'Me too.'"