Sexual Personality: Understanding SES and SIS

This article is an excerpt from the Shortform book guide to "Come As You Are" by Emily Nagoski. Shortform has the world's best summaries and analyses of books you should be reading.

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What determines your sexual personality? Why do different people seem to have different levels of sexual desire? Are some people biologically wired to want more sex?

Although everyone is born with the same brain mechanism that controls sexual response, certain aspects are distinct to each person. According to sex researcher Emily Nagoski, these differences produce unique sexual personalities that determine our individual sexual needs, such as what it takes to turn us on.

In this article, we’ll explore the two-system mechanism in our brain that determines our sexual personality, including what it is, how it works, and how it varies from person to person.

The 2-System Mechanism of Sexual Response

Why do different people seem to have different levels of desire?

To answer this question, researchers at the Kinsey Institute in the late 1990s developed the theoretical model that makes up our modern understanding of human sexual response. Their model describes a two-system mechanism in the brain that determines our sexual personality. Nagoski nicknames these two systems our sexual “accelerator” and “brakes,” but moving forward, we’ll refer to them as the Sexual Excitation System (SES) and Sexual Inhibition System (SIS), the model’s original terms.

Nagoski explains that the Sexual Excitation System (SES) is responsible for the process of arousal. It constantly scans our environment for potential sexual stimuli. (Common examples could be the scent of cologne or seeing our partner in a bathing suit.) When the SES identifies sex-related stimuli, it sends a signal from our brain to our genitals so that our body can prepare for sex.

In contrast to the SES, Nagoski says that the Sexual Inhibition System (SIS) controls the process of impeding arousal. The SIS scans our environment for reasons not to have sex (for example, the risk of unwanted pregnancy) and sends a signal to our brain when we identify something relevant. 

Turn Ons and Turn Offs

So if there are two systems in our brain that are scanning our environment for signs that it’s time for sex (or not), how do they know what to consider a turn on and a turn off? Nagoski explains that although we may assume this knowledge is innate, in reality we learn almost all sexual stimuli through culture. In other words, society teaches us what to find arousing and off-putting. 

(Shortform note: Culture has such a powerful impact on our perception of sexuality that people can view even the same body part through an entirely different scope in different parts of the world. For example, while in many western cultures a woman’s breast is likely to trigger arousal, in other communities, the breast is treated as a neutral body part in comparison to others, such as the buttocks.)

Discovering Your Unique Sexual Personality

Nagoski asserts that understanding the two-system mechanism of sexual arousal, especially in a culture that bases its sexual standards on the average man (who often has a more sensitive SES and less sensitive SIS), can reassure women that their experience of sex is completely normal, no matter what combination of sensitivities they have. 

(Shortform note: Research, including cross-cultural studies, supports the differences in sensitivity levels between men and women that Nagoski cites. For instance, researchers applied the model to Portuguese men and women, the results aligned with previous research demonstrating higher excitation and lower inhibition in men compared to women.) 

But this reassurance doesn’t simply come from knowing what the mechanism is and how it works. Nagoski argues that instead, it arises from developing an understanding of our unique balance—our unique personality. While it isn’t an exact science, asking ourselves some questions about our individual experiences can help increase our awareness of how we function and what we need. For brevity, we’ve simplified the questionnaire while retaining its major themes.

(Shortform note: Another potential benefit of understanding the nature of our own SES and SIS is that it can help us determine our sexual compatibility with our partner. Although differences in sexual personality don’t guarantee incompatibility, they may help us predict potential challenges in our sexual relationship that could threaten our overall satisfaction, such as one partner initiating sex significantly more than the other.)

Reflecting on Your SES and SIS

Here are some questions to help you think about your SES:

  • Do you become sexually aroused by your partner showing off their strengths?
  • What about when you fantasize about sex?
  • Does boredom often lead to thoughts about sex?
  • Are you aroused by particular scents or tastes?
  • Does the thought of someone or something interrupting sex have little effect on your ability to stay aroused?

If you answered yes to these questions, you most likely have a sensitive SES. In particular, Nagoski says this means you’re very sensitive to sexual stimuli, even things like smell and taste. If you answered no, you most likely have an insensitive SES. Specifically, Nagoski says this means you don’t easily respond to sexual stimuli and need to devote specific attention to become aroused. If you couldn’t provide a definitive yes or no answer, then you probably fall somewhere in between.

Now, here are some questions to help you think about your SIS:

  • Does stress prevent you from getting aroused?
  • Does everything have to feel “right” for sex to be enjoyable?
  • Does worrying about your partner’s attraction to you affect your ability to become aroused?
  • Does fear about your performance in bed inhibit your arousal?

If you answered yes to these questions, you most likely have a sensitive SIS. In particular, Nagoski says this means you must feel relaxed and trust your partner to become aroused. If you answered no, you most likely have an insensitive SIS. Specifically, Nagoski says this means you’re not worried about your performance, body image, or potential consequences of sex. If you couldn’t provide a definitive yes or no answer, then Nagoski says you’re most likely somewhere in the middle.

Sexual Personality: Understanding SES and SIS

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Here's what you'll find in our full Come As You Are summary:

  • Why women should change the way they talk, think, and feel about their sexuality
  • A look at the misinformation and harmful cultural messaging surrounding sex
  • A discussion around the individual experiences of arousal, desire, and orgasm

Darya Sinusoid

Darya’s love for reading started with fantasy novels (The LOTR trilogy is still her all-time-favorite). Growing up, however, she found herself transitioning to non-fiction, psychological, and self-help books. She has a degree in Psychology and a deep passion for the subject. She likes reading research-informed books that distill the workings of the human brain/mind/consciousness and thinking of ways to apply the insights to her own life. Some of her favorites include Thinking, Fast and Slow, How We Decide, and The Wisdom of the Enneagram.

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