Author Lora Leigh writes mainstream novels that often climb The New York Times best-sellers list. Her books are known for explicit sex scenes and graphic language, as well as for featuring alternative erotic lifestyles or menage a trois relationships.

So the Kentucky-based writer says she was shocked that the hype of “Fifty Shades of Grey” and its two sequels marked a new trend in fiction: sexually explicit scenes.

Leigh makes it clear that she’s in no way dismissing the success of “Fifty Shades.”

“A lot of people enjoy the book. I think it’s wonderful that it’s getting notice,” she says.

But she does wonder, when did writing books with explicit sex scenes become new?

She’s quick to mention longtime authors such as Bertrice Small, Iris Johansen and Linda Howard and said that while their descriptions were a little different (they didn’t use four-letter words) their writing laid the groundwork for today’s erotic-romance authors, including “Fifty Shades” author E.L. James.

“They were very sexy and very erotic,” Leigh said.

Author Sylvia Day, whose latest release, “Bared to You,” is currently ranked No. 4 on the Times best-seller list for trade paperbacks, concurs with Leigh’s assessment.

“It’s a long-established genre,” Day said.

Instead, erotic-romance authors say, “Fifty Shades” is a beacon that has brought attention to their work, in much the same way J.K. Rowling’s “Harry Potter” series resuscitated the children’s category.

At last count, 31 million copies of the “Fifty Shades” books have sold worldwide, 20 million in the U.S.

The plus side, said Day, is that “people finish and want to find something like it.”

Day said she has heard from people who have gone through her entire backlist of books since reading “Fifty Shades.”

North Texas author Shayla Black, who, like Leigh, has had books rising to the Times best-sellers lists for a while, calls “Fifty Shades” a gateway.

“People are coming out of the woodwork” looking for similar stories, said Black, who adds that demand has gotten to the point that her publisher is re-releasing her entire backlist. The first book in her “Wicked Lovers” series, “Wicked Ties,” is now in its 14th printing.

Romance fiction claims the largest share of the consumer book market, with annual sales of about $1.36 billion, according to the Houston-based Romance Writers of America. But it has long been dismissed.

“It’s a devalued genre,” said Jacqueline Lambiase, a journalism associate professor at Texas Christian University who studies the representation of gender and sexuality. She added that the response to romance is typical of a longstanding bias against women’s literature.

Leigh agrees that the entire romance genre has long been denigrated. “Romance writers have never been able to get away from the stigma,” she said. “People see the cover and make fun of them.”

Black said a double standard exists when it comes to romance fiction and sex. “I would love to know why James Bond can have sex with a blonde and it’s OK, but when the heroine of a romance has sex, it’s porn.”

The sex scenes in the “Twilight”-inspired trilogy about the tortured relationship of Christian Grey and Anastasia Steele prompted some to dub it “mommy porn,” a description that Lambiase and the authors take exception to.

“This prim and proper reaction denies that women are full sexual beings,” said Lambiase.

Day said she has fielded questions about “mommy porn,” or “mummy porn,” as it was called when she was in the U.K. recently for the launch of “Bared to You” in that market. “Usually only male journalists ask,” she said. She joked that there seems to be a surprise “that women like to read about sex.”

Susan Edwards, chief operating officer of Ellora’s Cave, one of the earliest e-publishers of erotic romance, said women of all ages write for the publishing line, and readers are equally diverse. “It’s erotic romance,” Edwards said. “It’s patronizing to call it ‘mommy porn.’ ”

The Internet and, later, e-publishing were key sparks in the current era of erotic romance. It allowed authors to push their work directly to readers, and it meant that readers didn’t have to read books with racy cover art that would prompt questions.

Ellora’s Cave launched after founder Tina Engler began selling her manuscripts online as e-books, using PayPal to collect.

Edwards said Engler decided to write because most of the books she read “stopped when it was just getting good.” Her submissions were rejected by publishing-house editors who told her, “Women will never read this.”

A single mother, Engler went from being a welfare recipient to a millionaire in five years, Edwards said.

Resistance to the rise of erotic romance wasn’t limited to the public and media. Day and Black both talk about pushback from mainstream romance writers, who objected to the explicit content.

Black has a canned spiel on the difference between erotica and erotic romance.

“Erotica is one person’s journey to self-actualization through sexual exploration,” she explained. “There’s no happily every after. The person just winds up in a different place. Erotic romance is the journey of two people to happily-ever-after: They just have a lot more sex.”