The phrase "mummy porn", used to describe Fifty Shades of Grey and its imitators, dismissed the predominantly female readership.

But the world of erotic literature is far wider than the phenomenon created by EL James and it appeals to many young adults.

Kay Jaybee writes a variety of erotica but is best known for her "more full-on, whips and chains" stories.

When she writes, she pictures her reader as someone like her, in her 40s.

"When I look at my sales figures, that's about 50% of my readership," Kay, who prefers to be referred to by her pen-name, tells Newsbeat.

"The other 50% are 18 to 26-year-olds. I guess they maybe do have a little bit more free time and may well be experimenting themselves.

"Or [they] may just enjoy the fantasy and like to see what options are out there, without having to actually physically do the things that I'm writing about."

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Kay says she is aware that the young people reading her books will potentially be learning about their sexuality, through her writing.

"There are things that perhaps, however open your family is, you couldn't ask your parents and you might not want to ask your friends," she says.

"It just gives you a little bit of information."

I write to help them escape for a few hours into a fictional world of romance and part of that is sex Alice Raine Erotica author

While Kay isn't directly targeting young adults, erotic publisher Xcite Books noticed a gap in the market a couple of years ago and some of its authors are now writing specifically for that audience.

Alice Raine's first series, Untwisted, was aimed at 18 to 30-year-olds.

She says she is careful to label her books as suitable only for those aged over 18.

But it's not just about the age warnings, these authors also believe they have a responsibility when it comes to the content.

"There's never any question of consent. There's never anybody underage. There's never anything illegal. There is no blood loss," says Kay.

"Even when things get slightly more rough in the BDSM stories, everyone is always allowed a get-out."

Readers of erotic fiction tend to be women, research done by publishers suggests.

"I think men prefer a visual stimulus where women like a more emotional connection. They like to read words, if they're [engaging with content about] sex," says Alice.

When I first started, I didn't tell that many people, mostly because I was quite shocked at myself because I didn't think I had it in me Kay Jaybee

"They can read books like this and see an almost near-perfect relationship which has got amazing physical relationships.

"I think they like to read it as a way of escaping for an hour or two."

Naomi Smart, who published her first erotic novel earlier this year, has a slightly different take.

"Women tend to be more open about reading erotica. It's not necessarily the case that men don't, it's just they choose not to share it," she says.

"Perhaps they may feel they'll be ridiculed for it."

Although both Alice and Kay aren't writing under their real names, most of their friends and family are aware of their books.

Having said that, they don't think their parents have read their erotic fiction.

"I don't want them thinking that's what I do at home," says Alice.

"When I first started, I didn't tell that many people, mostly because I was quite shocked at myself because I didn't think I had it in me," says Kay.

"I'm the least likely erotica writer in the world."

There are things that perhaps, however open your family is, you couldn't ask your parents and you might not want to ask your friends Kay Jaybee Erotica author

She adds: "I don't think I would have been able to tell my grandparents, I don't think they would have liked it."

Meanwhile Naomi is writing under her actual name and says she is "proud" to see it on the book covers.

"What I would like is for people to see there is no stigma anymore [about the sexual content in her books]," she says.

"We all like different things and that's OK."

Alice says she originally thought it a "little bit weird" that her stories may be incorporated by her readers into their sex lives.

"I find it quite amusing now really," she says.

"I wouldn't say I write to encourage people to try the things.

"I write to help them escape for a few hours into a fictional world of romance and part of that is sex."

Kay says that the way people use her books is "private" to the reader.

"You don't like to ask people too much because some people will tell you and you don't want to know," she explains.

"If I am giving you a good story to read and you are enjoying it then yes, job done."

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