What’s the difference between sexual desire and arousal? How does the contraceptive pill affect your sex drive? Which hormone has recently been found to boost sexual arousal in both men and women?
Hello and welcome to series 3 of Hormones: The Inside Story, the podcast from the Society for Endocrinology. Over the next six episodes, we're going to be delving inside the body to find out more about the little chemicals that make us tick.
I'm Dr Sally Le Page, an evolutionary biologist and science presenter, and I'll be chatting with a whole bunch of hormone scientists - or endocrinologists - to bring you surprising stories and cutting edge research.
Today we're asking, "Are my hormones making me horny?", so as you might expect, this might not be the best episode to have playing around younger listeners unless, of course, you're ready to answer a whole bunch of uncomfortable questions. You have been warned.
Are you feeling frisky? In the mood? Hot under the collar? Turned on? Looking for some action?
However you phrase it, sexual desire and arousal are very common experiences. And there's a good reason why: we humans ain't nothing but mammals, and we need to have sex to pass on our genes to the next generation. It's our biological mandate to get it on, so we've evolved all sorts of adaptations that make sure we do.
But what is it that makes us want sex? Are our hormones making us horny? Is it our environment that gets us excited? And what can we do when it goes wrong, when that loving feeling just isn't there?
Before we go any further with the euphemisms, let's make sure we're all on the same page. What does it mean biologically to be horny, and is there a difference between being turned on and having a hard on?
Kristen: Some of those things are very similar. So being horny or wanting something that would be considered desire. The physiological response that you just mentioned, that's actually what we call arousal.
Sally: That's Professor Kristen Mark, a sex and relationships researcher and therapist and the Director of Education at the Institute for Sexual and Gender Health at the University of Minnesota.
Sally: It turns out, there's a big difference between sexual desire and sexual arousal:
Kristen: Desire is the more psychological component, the motivation, the drive, whereas arousal is the physiological response like an erection or lubrication in the vaginal canal, for example. So they overlap certainly, but they are definitely very different constructs.
Sally: If desire is the motivation, does that make sex the reward?
Kristen: Sure. Yes. That is simplifying it. But desire is a motivation. Yeah. It's a motivational state that brings you toward or away from sexual behavior.
Sally: So although desire and arousal are two separate things, they do still affect each other. If you don't have the arousal needed for an erection or vaginal lubrication, it's less likely you'll have satisfying sex, which will in turn reduce your sexual desire. But similarly, if you don't desire sex or seek out sexual encounters, you're less likely to feel aroused.
Sally: A good example of this is the infamous 'little blue pill', Viagra. It has to be the best known drug when it comes to getting it on, but is that affecting desire or arousal?
Kristen: So that is directly affecting arousal. That is not impacting desire in any way. Viagra targets arousal response, vasocongestion, it targets blood flowing to the penis, and that is an entirely arousal response. Yeah, so it's not actually changing anything to do with the extent to which one might want sex directly.
Kristen: Now, it could be impacting that indirectly, simply because obviously one is more motivated to engage in sex when things are functioning properly, right? So if things aren't functioning properly, then that can negatively impact desire, because why would you wanna engage in it again if there's a limited response happening.
Sally: Now we know what we're talking about when we say we're feeling horny, we can start to look at how our hormones affect this. And if any hormone's going to affect desire and arousal, it's going to be testosterone. Testosterone is often called the 'male hormone', and it's widely known in pop culture for making men aggressive and making them want more sex. Can't get it up? Must be that you don't have enough testosterone. So more testosterone equals more arousal and desire, right?
Kristen: Testosterone is related to arousal and it can be seen to be related to desire, but really there's a lot of other factors that play a much larger role other than testosterone. So if you imagine pumping someone up with testosterone, but they're still not having satisfying sex, well, what kind of effect is that gonna have on their ability to enjoy that sex? Not probably much. With women's desire, we tend to see that we can pretty quickly rule out testosterone. That's sort of like the first stop to rule it out.
Sally: Ok, so testosterone isn't the be all and end all of sexual desire. What about so-called 'female hormones' then, like oestrogen and progesterone? Those hormones increase and decrease dramatically during the course of the menstrual cycle and then only tiny amounts are produced after the menopause: do they affect arousal and desire?
Kristen: Yes, around ovulation we see an increase in sexual desire, in drive, in horniness. Whereas, right after one’s cycle, there tends to be less lubrication response so a little bit lower arousal. And that is all related to your hormone levels throughout the cycle.
Kristen: Menopause, what we tend to see is that dip in oestrogen really results in a real decrease in arousal and that is due to lack of lubrication response. And also the vaginal walls lose some of that elasticity, which can cause painful sex too. So if you're experiencing sort of more pain, less arousal, of course that might impact your desire in a negative way.
Sally: Right, so less oestrogen after the menopause means less sexual arousal means less sexual desire. So is this a case of 'no sex please, we're postmenopausal?'
Kristen: For some people, their desire actually increases in the context of menopause because when women age, they become much more confident in their bodies. They become much more able to articulate what their sexual needs are and kind of in a way are like, " I'm done dealing with this societal pressure to do this, this and this. So I'm gonna demand what I want." And that empowerment that can kick in at that stage can be really powerful for sexual desire and can result in getting what you want finally.
Kristen: And so I think there's a balance between those things and it's not just a simple yeah, your desire just tanks at that age.
Sally: There's clearly a lot of factors that all work together to affect how horny you feel at any given time in your life. So far we've discussed natural fluctuations in hormones like oestrogen and progesterone and how they affect desire and arousal. But every day, millions of women take artificial hormones in the form of the contraceptive pill as a form of birth control. Anecdotally, you hear people say their sex drive changes when they go on the pill, but what does the data say?
Kristen: The research has been so interesting on this. It's been pretty mixed. What we tend to see is that, yes, the pill does seem to have some sort of an impact on desire, but it doesn't really impact frequency because the protective mechanism of being on the pill, in and of itself, protecting you from unintended pregnancy, that alleviates a level of anxiety that might have previously existed, that frequency of sex remains high.
Kristen: So, they might subjectively report lower sexual desire, but frequency still remaining high and pleasure and satisfaction are remaining high, which are fueling desire. So in that way we see really mixed results.
Sally: So if you're a single woman, going on the pill might reduce your level of sexual desire a little bit, but that's more than made up for by not having to worry about getting pregnant. Understandable really. But what about women in long term relationships?
Kristen: If you are looking at people who are in longer term relationships, we found that there wasn't a link between the type of contraceptive method someone was on, whether it was hormonal, non-hormonal, and the extent to which they desired sexual activity.
Kristen: Within the context of a longer term relationship, there's a lot of factors at play that could be impacting your sexual desire. Things like relationship satisfaction, sexual satisfaction. And being on the contraceptive pill, that hormonal impact is not having a driving effect on this.
Sally: There are clearly both hormonal and non-hormonal factors at play, but which are more important? As part of Kristen's job, she sees hundreds of people who come to her for help with low sexual desire or problems with arousal. How often does the root cause tend to be their hormones?
Kristen: Really infrequently. As a sex therapist, I would definitely send them to just get that ruled out and it's pretty rare that it comes back as like, oh yeah, your hormones are all over the place. That's a really rare result in those cases.
Sally: If it's not hormones, then what are these non-hormonal things that affect sexual desire?
Kristen: Yeah, so we can classify these things into three main categories: these individual level factors, which hormones would fall into, these interpersonal factors, and then societal factors, which are broader components.
Sally: Individual, interpersonal and societal. That sounds like a lot, so let's break it down. What are individual factors?
Kristen: Things like your stress levels, if you're worried about finances or if you have a big deadline. Sleep is so important. If you're exhausted, what's the first thing that goes off of your to-do list, right? If you're exhausted, it can be really hard to feel like you have the energy to engage in sex. So definitely sleep is one of those life factors, those individual level factors that I was talking about.
Sally: Makes sense. There's nothing sexy about a looming deadline or feeling knackered. What about interpersonal factors?
Kristen: Interpersonal factors are things like sexual compatibility, the extent to which you are happy in your relationship, your sexual satisfaction, your communication with your partner.
Sally: Yes, it probably does help if you feel good about your other half before you get it on. What about the last category, societal factors?
Kristen: Societal factors like the way that you were raised when talking about sex. Do you have shame or stigma surrounding sex? The patriarchal society that teaches women to be gatekeepers of sex. Couples who tend to talk more about their sex life tend to not struggle with desire difficulties as much. This talking about it and being able to be open and honest about your sex life with your partner, which is hard for people to do given the way that many people were raised to not talk about it, right?
Sally: It's clear from talking to Kristen that there are so many things that affect your level of sexual desire and arousal, from your hormones and relationships to just life in general. It's hardly surprising then that 1 in 10 people around the world experience low sexual desire, so low that they find it distressing. Wouldn't it be great if we could just hack our hormones and take a pill to make us feel horny? This sounds like a sci-fi fantasy, but in the last decade, we've made some remarkable discoveries that make a 'sexual desire drug' seem more and more realistic. And it's all thanks to a hormone that you've probably never heard of before, called kisspeptin.
Alex: Kisspeptin is the conductor of the brain chemical orchestra. So it's the sort of master regulator for downstream reproductive hormones.
Sally: That's Dr Alex Comninos, a hormone consultant at Imperial College Healthcare NHS Trust, who specialises in researching reproductive hormones and behaviour. He's been very interested in kisspeptin and has recently published some papers showing it can make people feel more horny. So what is this kisspeptin thing, how does it work, and why the heck have I never heard of it before?
Alex: So it was first identified as an anti-cancer gene back in 1996.
Sally: KISS1 is the name of the gene that encodes the kisspeptin hormone. But why did scientists who discovered a cancer gene give it a name about kissing?
Alex: This is a really, almost incredible, story. So it was first identified at Penn State University in the city of Hershey. And perhaps you are more familiar with Hershey as the Hershey's Chocolate Factory. And their most famous products are Hershey's Chocolate Kisses. And so they named this newly identified anti-cancer gene after the Hershey's Chocolate Kisses. And it wasn't until 2003 when it was identified to be essential for reproduction.
Sally: That's a pretty amazing coincidence.
Sally: Considering kisspeptin was only discovered in the last 30 years, it turns out to be important at controlling lots of things in the body.
Alex: Kisspeptin can influence metabolism, audition, cognitive function, mood and depression, fear and anxiety. So it looks to have a number of roles all over the body, from the brain to the pancreas, the small intestine, the liver, the bones, the placenta.
Sally: It seems like there's nothing this little hormone doesn't do! But what we want to know is how does it affect sex?
Sally: As with a lot of things in the body, the answer is: it's complicated. As a hormone, kisspeptin sets off a chain of events that eventually, through a very long-winded process, means your body produces more oestrogen or testosterone after a couple of hours. But kisspeptin doesn’t just affect the sex hormones. It also directly affects our brains, especially the parts of our brains that process, you guessed it, sexual desire.
Sally: Professor Julie Bakker works at the University of Liege in Belgium, and has spent the last few decades studying mice in the lab to help us better understand what's going on when they're getting it on.
Julie: I'm interested in sex differences in the brain and behaviour. I started these studies quite a long time ago, to be honest, like 2005. That's when we really started to test kisspeptin as a potential stimulator of sexual behaviour in mice.
Sally: Julie was working with some mice that had been genetically altered so that their brains couldn't make kisspeptin.
Julie: This mouse model was showing less sexual behavior and was less sexually motivated.
Sally: This was the first evidence that kisspeptin directly affects sexual motivation. But this is all happening in mice. How on earth can you measure sexual desire in a mouse?
Julie: Well, you cannot really talk about sexual desire, of course, in the mouse, because they're animals and we can't ask them personally if they have any desire, right? So basically we are looking at stereotypical behavior actually in rodents.
Sally: And what is stereotypical sexual behaviour for a mouse?
Julie: So when rodents mate, the male will mount a female, and the female will show sort of this receptive behavior. She will show lordosis, which is like arching of the back. And so this allows the male to fertilize the female. So that's one way actually of looking at female sexual behavior is looking if she shows lordosis behavior when she's mounted by a male.
Sally: As well as looking for this back-bending behaviour, Julie also tests how frisky her mice are feeling by doing a sniff test. Scent is really important for mice, especially during mating. If a female is seeking out a mate, she'll spend longer sniffing at the scent of a male mouse versus the scent of a female mouse, so Julie can use that preference as another way to measure sexual behaviour.
Sally: Remember those female mice that had been genetically altered so they didn't make kisspeptin?
Julie: They will not show the typical lordosis behavior when she's mounted by the male. She'll actually get quite aggressive with the male. She's showing these rejection behaviours. In addition, she's no longer interested in really sniffing out male odours as well.
Sally: Both signs that these females without kisspeptin are less interested in sex.
Sally: But what happens if you go the other way and give mice MORE kisspeptin than they're used to? If you inject kisspeptin into a mouse that otherwise wouldn't be in the mood for sex?
Julie: We observed indeed that kisspeptin, just injected, increased the preference for sniffing the male odour and she was ready to show the lordosis behavior when she was mounted by the male which we did not observe when not giving the kisspeptin.
Sally: This means that for female mice, if they don't have kisspeptin, they're not interested in sex, and if you replace the missing kisspeptin, it makes them more interested in sex again. Julie and her team spent ten years doing more of these sorts of experiments with mice before publishing their results in 2018.
Julie: So it took a long, long time, but because we wanted to get the maximum amount of evidence together showing that kisspeptin strongly stimulated female sexual behaviour.
Sally: But once they published their paper, what came next was a bit of a surprise..
Julie: It was crazy actually. I hadn't expected anything like this. You know, you just publish a paper and somehow it got picked up by journalists. And so it was in the newspaper and then I got so many emails and calls from women that were kind of desperate to get kisspeptin and, you know, this could be the new thing basically for women that are suffering from low sexual desire.
Sally: And remember, this is all in response to a paper about sexual behaviour in mice. Not in humans. Mice.
Sally: As you can tell by the many emails Julie received, there are plenty of people around the world who feel distressed by the lack of sexual desire they experience. Here's Alex Comninos again:
Alex: So it's termed hypoactive sexual desire disorder. And this can affect up to 10% of women and men worldwide. It's quite a prevalent health condition. The predominant theory in HSDD is that there's an excess of overthinking, an excess of introspection and self-monitoring. You know, how do I look? How long will I last? What does my partner think? And negative thoughts like that basically suppress the downstream more raw sexual arousal and desire.
Sally: Right now, the main option for people with this distressingly low sexual desire is cognitive behavioural therapy with sex therapists like Kristen. But are there any drugs that can help boost desire?
Alex: Unfortunately at the moment, you know, there's very limited treatments. In America there are two treatments that are licensed there for premenopausal women, but they have significant side effects, which include dizziness, sedation and nausea, and interactions with alcohol, none of which are ideal during a sexual encounter. And, in men, unfortunately there are no current treatments.
Sally: Back at Imperial College around the same time, Alex and his colleagues were researching kisspeptin and sexual behaviour but in humans rather than mice. Over the last 8 years, they’ve done experiments to see how kisspeptin can affect sex drive and arousal.
Sally: If you're wondering how to go about measuring horniness as part of a highly controlled scientific experiment, the answer is... first put your participants in an MRI scanner...
Alex: Essentially you are applying a magnetic field to the brain and monitoring the feedback from that. And so you can generate a map of the brain activity and therefore you can say, yes, in this area there is enhanced brain activity, or in this area there's decreased brain activity.
Sally: Then you show them porn while scanning their brains...
Alex: In this study, we were just using images so they viewed erotica. In the more recent studies, they actually watched videos.
Sally: And you ask them a bunch of questions...
Alex: We do questionnaires as well. So there are certain well-established questionnaires for looking at sexual arousal and desire
Sally: This includes questions like: on a scale from 0 to 5, do you feel seductive? Excited? Do you have quivering sensations? It is quite the questionnaire!
Sally: By injecting half your participants with kisspeptin, you can compare which bits of the brain light up:
Alex: You do it with a placebo, and then you do it with kisspeptin and see what the difference is.
Sally: It's not exactly my idea of a good time, but what about the results? Alex started by testing healthy men with a normal sex drive.
Alex: So our first study was back in 2017. We basically showed that administering kisspeptin to healthy young men had an effect of amplifying brain activity in sexual arousal areas. And what we found is that the more their brain was activated by kisspeptin, the less averse the participants were to sex, so essentially they were more up for it.
Sally: So just like in the mice, giving human men kisspeptin made them more interested in sex by changing their brain activity.
Sally: But what about kisspeptin as a treatment for the hypoactive sexual desire disorder we mentioned earlier?
Alex: So this was a group of 32 men with low sexual desire that was distressing to them and was not caused by any other medical condition. They were given kisspeptin and we basically found that in their brain activity there was this deactivation in areas related to overthinking, self-monitoring and this excess introspection. How do I look? What does my partner think? How long am I going to last?
Alex: We also found that the men reported feeling happier about sex. They also reported feeling more flush, which is a frequent sensation during sexual activity.
Alex: And most importantly, penile rigidity went up by 56% above placebo suggesting a pro erectile effect of kisspeptin.
Sally: Yes, you heard that right, in this study they also measured how hard their hard-ons were. And to put that 56% in some context...
Alex: Viagra is normally above 50%, so we're in the ballpark of Viagra, which is exciting, yes.
Sally: So the men not only felt happier about sex after being injected with kisspeptin, we could also see that sexy boost manifest in their brains and...elsewhere in the body!
Sally: But for everyone sitting at home wondering - what about the women? Well Alex also administered kisspeptin to 32 premenopausal women in another research study...
Alex: Here we found that again, there was this deactivation in areas related to this overthinking and introspection. And with that, the participants reported themselves feeling sexier when they were given kisspeptin compared to placebo.
Sally: Just to reiterate, these experiments involved watching porn inside a MRI scanner knowing you're being monitored by researchers. And despite this being the least sexy environment I can think of, both men and women felt sexier when they were given kisspeptin.
Alex: It is quite encouraging to get these results in the exact environment that you talk about, in a small, white, claustrophobic tunnel. It's cold in there. You can hear this noise of these magnets moving around and you're watching it on a television.
Alex: So, you know, we're hopeful if you can get these types of results in a scanner. What might you get in a more natural environment such as a participant's home or bedroom?
Sally: This is a huge breakthrough! Kisspeptin, a hormone that the body produces naturally, can increase sexual desire in both men and women. And because our bodies already make kisspeptin, adding a bit more doesn't seem to have too many side effects...
Kristen: What is promising about this is that the side effects seem to be relatively mild, and a lot of these other drugs that have potentially been seen they've had such severe side effects that it just makes it not worth it. We're trying to improve people's lives, not make them more difficult in order to have one more satisfying sex event a month, right?
Sally: So what needs to happen now before we see kisspeptin on the pharmacy shelves?
Alex: We have to, you know, determine the correct dosing, the correct dosing intervals. We're doing some current work looking at administering kisspeptin as a nasal spray.
Julie: What needs to be done? There's still a lot of work ahead. I would say to look really at women depending on different phases of the cycle, how it would work in women taking the birth control pill, like, how is it actually in postmenopausal women compared to premenopausal women?
Sally: It's natural to compare kisspeptin with Viagra; some headlines have even called it 'mental Viagra', but is that an accurate moniker?
Alex: In terms of mental Viagra, I would say that you know, there's some truth to it
Alex: Viagra, as we know, is predominantly a vascular agent acting on the plumbing in the genitals. And here you've got an agent that can actually act on the core issue, which is often low sexual desire. So here we're trying to treat the core problem. There are a lot of men out there who have low sexual desire and they're prescribed Viagra. And for the majority, it's not gonna have any effect. And I've had people email me since saying, you know, my GP has given me Viagra, but I just walk around with an erection, but I don't want sex.
Alex: It's not really very helpful to them. Whereas if we can find a treatment that can increase their desire and arousal, then that's the sort of magic answer for a lot of people
Sally: Based on the research we have so far, we think kisspeptin is turning down the volume of the part of the brain for overthinking, self-monitoring and self-judgement. That sounds just like the issues Kristen finds her clients are suffering from; the societal shame and stigma surrounding sex, worrying about what your partner is thinking, being too stressed to actually live in the moment, right?
Kristen: Yeah, it does. And I think this research is really promising and has a lot of potential.
Kristen: But sexual desire in anybody is very contextual. It is something that has a lot of nuance.
Kristen: So with any medication, I mean for any psychological issue, pairing the medication with therapy results in the best possible outcomes. And so perhaps that's part of the key here too...
Sally: Now, I don't know about you, but I'm feeling a little hot under the collar - I'm off for a quick lie-down in an MRI scanner.
Sally: That's all for now. Thank you to all our guests, Professor Kristen Mark, Dr Alex Comninos and Professor Julie Bakker.
Sally: Next time, we'll be asking, "Can my pet pick up my stress", and meeting a dog that can detect life-threatening stress hormones...
Michelle: I just thought it was the most annoying pup, but clearly he was a clever pup that was just trying to save my life.
Sally: Learning the scientifically tested way to stress someone out...
Clara: It was amazing how panicked it did get people, it was certainly quite stressful.
Sally: And uncovering the number one way we are stressing our pets...
Ruth: They don't look in the mirror and think, I need to get to the gym. What it does is it changes the animal physiologically.
Sally: Hormones: The Inside Story is a podcast from the Society for Endocrinology. Explore more about the world of hormones at yourhormones.info and follow them on twitter @your_hormones
Sally: The show is a First Create the Media production. It was researched, written and produced by me, Sally Le Page and Emma Werner. Our executive producer is Kat Arney. Thank you for listening and we'll see you again soon.
REFERENCES
Impact of Contraceptive Type on Sexual Desire of Women and of Men Partnered to Contraceptive Users
Maintaining Sexual Desire in Long-Term Relationships: A Systematic Review and Conceptual Model
KiSS-1, a Novel Human Malignant Melanoma Metastasis-Suppressor Gen
Female sexual behaviour in mice is controlled by kisspeptin neuron
Kisspeptin modulates sexual and emotional brain processing in humans
