For those unfamiliar with the genres, erotica and erotic romance might seem the same: stories about sex. But a closer examination reveals a lot more. As in most literary genres, certain tendencies attract readers, enjoy a brief moment of popularity, and lose traction—possibly to be renewed years later by another author.

Before getting into trends in erotica and erotic romance, it’s important to describe the two, which, like stepsiblings, are only sort of related.

Erotic romance, according to a definition from the Romance Writers of America, refers to “novels in which strong, often explicit, sexual interaction is an inherent part of the love story, character growth, and relationship development and could not be removed without damaging the story line.”

And erotica? “Erotica is just people doing it,” says Cordelia Logan, who has written 19 stories under five pen names and is beginning to focus on BDSM. (To maintain privacy, she declined to reveal her pseudonyms.) “[Characters] are having sex in interesting ways and with interesting people,” she says. “There’s not a lot of character development. The plot revolves around how these people are going to do it, and what’s getting in the way.”

Appealing to Readers

Last year, the author Peter C. Hayward, who writes erotica under the name Pandora Box, published a now-deleted blog post outlining what he calls the “Golden 12” erotica genres that find consistent readership: those featuring billionaires and other “modern alpha males”; incest and pseudo-incest, which includes relations between women and their stepfathers and men and their adopted sisters; shifters; monsters; students and teachers; gangbanging; cuckolding; gender swapping; sleeping or unconscious sex; ménage à trois; and cowboys.

Trends in erotica tend to emerge as kinks written into those popular genres. Many erotica writers point out that while the Golden 12 have been around for a while, situations like breeding—in which a male character hopes to impregnate a female character to trap her in a relationship—have seen an increase in popularity recently.

“Breeding is definitely in right now and will most likely be in for another six months or so,” says Amy Cooper, who has authored numerous how-to guides on self-publishing erotica, including “Publishing Erotica: How to Make Your First $1,000.”

Many trends are cyclical. The two anonymous authors who have published more than 30 erotica stories on Amazon under the pseudonym Alexa Riley say breeding was in vogue about 10 or 15 years ago and has only recently made a resurgence. Riley’s popularity might have even helped spark that.

After they included “light” breeding in a Riley book, the authors noticed that people kept highlighting it on their Amazon Kindles. (Authors can see what people who use Kindles home in on while reading). “I wanted to see what would happen if I pushed it,” the authors say, speaking in the unified voice of Riley. They aren’t sure what exactly is driving the current popularity of breeding, though they note that previous breeding stories weren’t packaged very well compared with their modern counterparts.

Pushing out shorter works with more exotic kinks is a valuable way to get insight into what the audience wants to read. “A lot of times, I’ll do a smaller book and see how people respond to the kink,” the authors say. “If it does well, I’ll write a full length novel. The breeding thing did really well, and it’s blown up.”

Cooper says erotica trends “come quickly and leave slowly.” That means it’s important for authors to take advantage of what’s hot and what’s likely to become hot. “It’s usually when two currently popular kinks are mashed together to create something new,” Cooper says. “Ménage is hot, as is breeding, werewolves, and billionaires. A new trend could be two billionaire werewolves breeding women for their own dark purposes.”

Steamy Sloppy Storybook Romance

Trends in erotic romance tend to be less kink driven, in part because the genre is more story-oriented. “I think tropes are our version of kinks,” say Bree Bridges and Donna Herren, who publish together as Kit Rocha. Popular tropes currently include romancing a best friend’s little sister, marriages of convenience, and forbidden romances.

What’s popular in erotica is often also popular in erotic romance, despite the comparative lack of kink in the latter. “[Readers] all like alpha males,” the popular erotic romance author C.M. Steele says. “And everybody goes for stepbrothers.”

Though erotic romance authors generally write longer and don’t publish as frequently as erotica authors—who might churn out one or more stories per month—they also try to chase what’s popular. “Stepbrothers were the most common trend last year,” says author Minx Malone. “And that affects you when you’re writing.” Malone, whose books have been on the New York Times and USA Today bestseller lists, first published erotic romance novels in 2007 with Ellora’s Cave, but she began self-publishing in 2011 and is now entirely self-published.

Getting away from the influences of traditional houses has allowed Malone to push the boundaries of her genre. “It’s not even pushing kink boundaries, but pushing the boundaries of what we’ll accept for a hero or heroine,” she says. “For a long time, romance was very traditional.” The alpha male’s continued popularity, for example, is a holdover from the demands of the old romance publishing houses, she says.

Thanks to the rise of self-publishing, however, authors can now experiment more. “Maybe the woman is in power,” Malone says. “I have a friend who writes about female billionaires. She’s flipped that paradigm. Those boundaries would not be pushed in a traditional situation. That’s the most common thing I hear from people writing for houses: it’s hard to do something different.”

As in erotica, mash-ups can be an effective way of igniting a new trend. Malone recently introduced her Blue-Collar Billionaires series, in which working class men discover that they have a billionaire daddy. “I was shocked that my billionaire twist worked,” Malone says. “I didn’t expect it to be a full series. I thought it’d be a side book that I’d write for fun. That’s the attitude you have to take if you’re not sure it’s going to work.”

Meanwhile, Rocha’s Beyond series—currently seven books in—combines dystopias with motorcycle gangs and cage fighters. “We’re not jumping on any new trends,” the authors say. “I see them go by, but we’re not shifting gears.”

The Unpredictable Amazon

Any story about trends in erotica or erotic romance must reckon with Amazon’s impact on the genres. The company’s dominance as an e-book distribution platform—and its squeamishness toward sexual content—gives it tremendous influence in determining what’s popular, as it dictates what can and cannot be easily purchased.

“It really all comes down to Amazon,” says Cooper, who has published her how-to guides through the retailer. “It always has. They say no to something, and it completely cuts out a portion of the market.”

In addition to banning overly explicit covers, Amazon forbids certain words. It is taboo to mention “breeding” on the cover, for instance. “A lot of authors try to write around it and change lingo and things like that,” the authors who write as Riley say. “So it turns into ‘she wants babies.’ ”

Even the acceptability of those work-arounds can change, Cordelia Logan says: “Lately, Amazon has been cracking down on the ways you can use euphemisms.”

But Amazon is vague about what it does or doesn’t allow. A company spokesperson pointed to Kindle’s content guidelines. Offensive content, as defined by Amazon’s website, is “probably about what you would expect.” That lack of clarity isn’t likely to change. “They keep it vague on purpose,” the authors behind the Rocha pseudonym say. “The minute they codify it, people will walk as close to the line without going over.”

As Logan points out, the consequences of raising Amazon’s ire can lead to removal from the platform or having books rendered unfindable, even if a reader is typing an exact title into the search field.

“It’s complicated selling books that are sexual on Amazon,” Rocha’s authors say. “When we were ready to release our third book, Amazon thought the cover was too sexual. We got hidden from searches. We rebranded our series. We had the same cover three books in because people couldn’t find us. It’s complicated, and it’s hard sometimes to walk the line.”

Natural Selection

Amazon’s business practices also influence the way erotica and erotic romance are published. The advent of Kindle Unlimited, which gave authors 30¢ each time their stories were read, regardless of length, drove a wave of writers onto the platform, many hoping to make a quick buck by publishing an array of short pieces. Since Amazon changed the Kindle Unlimited model to pay authors on a per-page rate, there’s no longer an economic benefit to publishing frequently and short.

There were other reasons why so many authors joined Amazon in 2015. “I saw a bigger spike of people when Amazon started kicking out the monster erotica,” Logan says. “People were so shocked it existed. There were a lot of think pieces about it in Business Insider and Jezebel, and that attention drove a lot more people.”

But self-publishing erotica or erotic romance can be a grind, and the volume it demands can make it a grueling one. Logan notes that the herd is beginning to thin. “People thought it was a get-rich-quick scheme when they heard about girls making $100,000 on Amazon,” Logan says. “Then they realized it’s a job. You have to be consistent.”

Malone says that in 2015 the market was glutted with work that was subpar. “But I’m a huge believer in economics,” she says. “Readers are extremely smart, especially romance. They are very exacting, and they’ll start exercising their power with their pocketbook. It’ll be very important this year to hold your work to the highest standards possible.”