Evolution may provide one explanation.
Feet. Feces. Statues. These are such common fetish objects that experts have given them names. (Coprophilia, by the way, is an arousal to shit.) Sexual fetishes don't stop at objects, either: Specific settings and scenarios—everything from caves to foggy weather—are well documented in the existing fetish literature.
To fully understand this concept, it's first important to differentiate a true fetish from fetish behavior. "The clinical definition of a fetish is that you need this object or activity to be aroused, but that's pretty rare," says Justin Lehmiller, director of the social psychology program at Ball State University and a faculty affiliate at The Kinsey Institute. "It's far more common for people to enjoy fetish sex on occasion"—BDSM being the most popular example—"but not truly have a fetish."
Whether you're a dabbler or a full-on fetishist, however, it's not always clear where these sexual proclivities come from. What we do know is that a person's personality and sexual history likely play a role. "Habituation might make a more frequent behavior seem dull after a while," says Roland Imhoff, a professor of psychology at Germany's Johannes Gutenberg University who has authored research on fetishes and sexual motivation.
Imhoff compares "vanilla sex" to eating the same kind of pizza every night for dinner. Even if you love pizza, you're going to get tired of eating the same pie night after night. Likewise, white bread sex may grow boring—especially for people with a high sex drive who are doing it all the time, he says. That boredom may lead you to try novel and increasingly exotic forms of sex—including sex that incorporates fetish objects. If that experimentation leads to excitement and—the ultimate payoff—an orgasm, you may be more likely to revisit unusual or "deviant" forms of sexual adventurism, he says.
That helps explain BDSM and some of the more common forms of fetish sex. But how does a person develop a serious attraction to less widespread fetishes—like sex in caves? Or around wood? The most likely explanation is that a person is exposed to something unusual or exotic during an especially pleasurable sexual experience, Lehmiller says. Maybe a woman has amazing sex in a cave, or a guy spends his childhood enthusiastically masturbating in his dad's woodshop. These events could form powerful associations in the brain—associations made all the more powerful because they were rewarded with an orgasm.
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Once that reward pathway is formed, the association between the fetish object and sexual pleasure will be strengthened every time that person has cave sex or plays with himself around wood. And despite what you might guess, there isn't a big Freudian or subconscious element to all this. Lehmiller says most fetishists can remember a specific sexual event or encounter that kicked things off.
But even that theory doesn't always account for what may be one of the most polarizing fetishes of all: poop. Fecal matter is inherently revolting to most of us, but researchers actually have a theory as to how someone could develop an attraction to it.
Research shows that, when people are aroused, their disgust reflex basically shuts down. That makes sense from an evolutionary perspective; soap, toilet paper, and breath mints didn't exist for most of human history. Sex was a dirty, smelly affair. If arousal didn't overpower our disgust toward bodily fluids and excretions, our species wouldn't have lasted long.
Lehmiller offers a hypothetical: "Maybe a guy is in the shower with his girlfriend, being intimate, and she urinates on him," he says. Because the man is aroused and his disgust reflex is muted, he may find he enjoys the introduction of human waste into the equation. "I've heard stories like that," he adds. He also points out that anything considered taboo is likely to kindle excitement. If you're the type who gets a thrill out of the forbidden, exposure to urine or shit during a sexual experience could—emphasis on could—stimulate a new fetish.
Your personality may also play a role. "There are probably some traits that predispose people to enjoying fetish sex," Lehmiller says, adding that sensation-seeking is one example. Or it could simply be how you're wired: One study suggests that the areas of the brain that light up in response to pain and pleasure have a lot of overlap; crosstalk between these overlapping networks might help explain why BDSM is so popular.
But there's still a lot we have to learn about how these associations develop. And it's important to note that not everyone who has awesome sex in a cave, or in a wood shop, or around poop, for instance, is going to develop a taste for it. As Lehmiller puts it, "It's a complex question, and I think there is more than one answer."
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