BDSM is at its core about power (not pain). An apparent power imbalance can be exciting in a sexual context. Some like to be in complete control and some like to surrender control, to relax, to be freed from responsibility. This exchange of power is usually of limited scope, either for the duration of a single session that lasts from a few minutes to a few hours, or within the sexual context of an ongoing relationship that only occasionally or selectively involves other areas of their lives. 24/7 adherence to established roles (known as total power exchange) though common in erotic fiction occurs only rarely in actual practice.

There is a commonly held view (reinforced by the widely read 50 Shades books) that interest in BDSM is a result of early trauma, psychological condition, or difficulties with more conventional sex. But this view is not supported by science.

A 2008 study surveyed 19,307 people aged 16–59. Approximately 2% had participated in BDSM within the previous year and “they were no more likely to have been coerced into sexual activity, and were not significantly more likely to be unhappy or anxious... Engagement in BDSM was not significantly related to any sexual difficulties. Our findings support the idea that BDSM is simply a sexual interest or subculture attractive to a minority, and for most participants not a pathological symptom of past abuse or difficulty with ‘normal’ sex.”

A 2006 study administered 7 psychometric tests to 32 self-identified BDSM practitioners. These individuals were no more likely than the general population to experience depression, anxiety, obsessive-compulsion, psychological sadism, psychological masochism, or PTSD.

In order for a sexual behavior to be considered problematic it must cause distress and impairment. Most people who participate in BDSM experience no distress (and if they do it stems from the social stigma attached to BDSM activities rather than the activities themselves). As far as impairment, there is no evidence to suggest that there is a causal relationship between BDSM and sexual dysfunction and it also has no apparent effect on the ability to form intimate relationships.

These sorts of misconceptions about BDSM likely arise because it can superficially resemble physical or emotional abuse. But when done properly everyone involved is fully informed and enthusiastically consenting. There is frequently a negotiation process where they discuss what they want and don’t want to occur. And during the activity although there is an apparent power imbalance, both people are achieving some form of satisfaction and both people have the option to withdraw consent at any time and call immediate halt to the activity.

If it isn’t pathological then why do people do it? People have kinky sex for all the same reasons they have more conventional sex. It feels good. It’s fun. It connects them to their partner. But many BDSM activities are not what most people would consider fun and pleasurable. Often (though certainly not always) they involve stimuli that are usually considered painful. However, pain and pleasure are physiologically closely related. Pain triggers a release of endorphins inducing a chemical high. Whether the person’s subjective experience is one of pain or pleasure depends entirely on the context. If they are aroused and intent on engaging in a pleasurable activity with a trusted partner then sharp pain (such as a slap or spank) can be interpreted as intense pleasure.

But obviously not everyone feels this way. Why does it appeal to some people and not others? Preliminary results of a 1980 study indicate that BDSM tendencies may have a genetic component. Identical twins were more likely to share an interest in being spanked and whipped than fraternal twins.

You might suspect that childhood discipline and corporal punishment is an important factor in deciding whether or not someone develops an interest in BDSM. But kinky people do not report that their upbringing was exceptionally strict or that they were corporally punished more frequently.

But it is not uncommon for kinky people to have first encountered these desires in the course of normal childhood play, which indicates that (at least for some) it’s tied to genetics and/or very early childhood development. I experienced my first sexual feelings (that I can remember) when I was between the ages of 4 and 6. I discovered that I liked spanking one of my dolls. It was a weird and confusing kind of liking, which I now recognize as sexual. Others report similar experiences. Girls who tied up their Barbies and put them in cages. Boys who never wanted to be the cop but the robber who was cuffed and jailed.

Others discover their interest later, at the same time and in the same ways they learn about more conventional sex. Their father’s porn magazines, internet fanfiction, conversations with friends. And some are introduced to it later still by a partner.

So who are these kinky people? They are people who are ordinary in every other respect (as much as it is possible for anyone to be ordinary). They are no more likely to be suffering from trauma or mental disorders than anyone else. They are not social outcasts who can’t get laid and can’t hold down a job. They form communities and have the same socio-economic status as the general population. Even if you’re not in a BDSM community, it’s likely that you know some seemingly normal secretly kinky people.