The Science of Sexual Arousal: From Physiology to Psychology

Arousal may be spontaneous, or arise in response to sensory stimulation, memory, fantasy or emotional connection. Here’s how to understand the differences

What turns you on? Depending on the person, the answer to that question will vary wildly. But what is really going on under the, ahem, hood when we start to get in the mood?

The first scientists to really take the physiology of sex seriously – or at least break the taboos around talking about it – were William Masters and Virginia Johnson, sexologists who began their studies in the 1950s (and got married in 1971). “They came up with what’s known as the four-stage model, which was that the body gets aroused, you hit a plateau, you have an orgasm, you go back down to baseline,” says Dr Angela Wright, a GP and clinical sexologist based in Yorkshire.

“But what’s interesting about that is there’s nothing about actually wanting sex. It was like it just fell from the sky, rather than that there was any kind of desire that went along with the process. So subsequent models have asked: what is it that makes humans want to have sex? And what we see, typically, is that in male bodies, desire is usually experienced more like hunger; but in female bodies, especially in longer-term relationships, 75% of the time it’s more like walking into the supermarket, smelling bread and realising you want to eat.”

To put it another way, part of our desire seems to be spontaneous and another part responds to environmental cues, some of which we respond to because we associate them with the memory of a “reward”. Some of this response is hormonal – testosterone and oestrogen levels do have an impact on how much we think about sex – but much of it is behavioural.

“Signals from sight, touch, memory, fantasy or emotional connection activate networks in the limbic system and hypothalamus in the brain, and those signals travel through the nervous system to the body,” says Dr Ben Davis, a GP specialising in sexual medicine and sex therapy for men. “But people experience arousal differently. Some notice physical sensations first: warmth, genital tingling, a quickened pulse. Others need mental or emotional stimulation before their body responds. Most of us are somewhere in between. Understanding whether you’re more body-first or mind-first can help you create better sexual experiences.”

“Sexual arousal is a much more multifaceted, complex process than the straightforward, feral response it’s often assumed to be,” says Alix Fox, a journalist and PhD researcher in sexual wellbeing at University College London’s Institute for Global Health. “Appreciating that can help us be kinder to ourselves if our libido isn’t functioning as we want it to, or we’re experiencing kinks that confuse us.”

After these initial signals, our parasympathetic nervous system (often thought of as the “rest and digest” bit) takes the lead, triggering the release of nitric oxide. “That relaxes smooth muscle and allows more blood to flow into erectile tissue in the penis, clitoris and vulva, causing engorgement, lubrication and heightened sensitivity,” says Davis. “At the same time, neurochemicals like dopamine help drive desire and motivation, while oxytocin supports emotional connection and touch. Together they help the body shift from vigilance into a state where sexual response is possible.”

Though some of the mechanics are the same, what happens next depends on the equipment you’re working with. “In women’s bodies, there’s an arousal response that’s sometimes called ‘tenting’, where the uterus lifts and the upper vagina opens to help with penetration,” says Wright.

“It’s also probably helpful to note that there are two different ways that people can get the rush of blood that causes penile or clitoral erections. First, there are the reflex ones that come from the spinal cord without any correlation to your brain thinking about sex at all – they just kind of clean out the pipes with a big rush of blood to bring in some oxygen and keep everything healthy. This is really important, because the body keeps the brakes on sexual arousal, and the erectile tissues are kept slightly deprived of blood. If we lose reflex erections due to age or disease, the tissues gradually deteriorate and respond less well.”

The other kind of arousal is the one we get in response to thinking about or wanting to have sex, or sexual touch. “That triggers us to think actually sex is on the cards and our body’s going to get ready for it,” Wright says.

In the penis, when the blood rushes in, it swells up rods of erectile tissue – and eventually, these compress the veins on the outside that are meant to drain them. This traps the blood and makes the tissues rigid enough for penetration. “In female bodies, things are slightly different,” says Wright. “Blood has to keep on flowing in the whole time to sustain a clitoral erection, which is why sometimes it feels like things ebb and flow a bit differently.”

Apart from nitric oxide, the key neurotransmitters involved in this process are dopamine, oxytocin, noradrenaline, adrenaline and acetylcholine, and there’s a constant balancing act between them, depending on which part of Masters and Johnson’s four-step process we’ve reached. Dopamine is important for motivation, desire and reward; adrenaline helps with excitement; and oxytocin helps with bonding and trust, especially after an orgasm. Another key point is that for all of this to happen, the sympathetic nervous system (“fight or flight” mode) has to stay quiet: if you’re stressed or anxious, it can act as a biological brake, constricting blood vessels and stalling the whole process.

“Good sexual experience needs a certain amount of sympathetic arousal balanced with parasympathetic safety – you want to be excited rather than anxious,” says Davis. “If the sympathetic drive is too high – because of too much fear, or being hypervigilant to danger – it can kill arousal.”

What does this all mean for you? First, it means if you’re stressed about other things, you shouldn’t feel bad for not wanting sex. “An overloaded brain, overthinking, stress or anxiety can all inhibit our ability to not only experience sexual arousal, but to give our attention to things that feel good enough to encourage it,” says Kate Moyle, psychosexual therapist and author of The Science of Sex. “Stress and anxiety are also common interruptors of not just pleasure but also sexual functioning.”

It’s also important to note that, if you’re noticing a drop in desire, it may be a symptom of other changes in your body or life. “Women after menopause or breastfeeding may not have very good sensation, which means they don’t get a very good reward from bothering [to have sex]. So, as a partner, you have to appreciate that and be helpful in creating opportunities to be turned on,” says Wright. “You also have to be honest about what gives you pleasure, because humans are really simple: we do things we enjoy. If something is making you feel bad about yourself, or ashamed, or you get some negative consequence, you’ll find your behaviour changes because of that.”

For other people, sexual symptoms can be early-warning signs of cardiovascular, hormonal or mental health problems. “Many people assume it’s just part of getting older if erections become weaker or desire fades, but persistent changes are worth discussing with a doctor,” says Davis. “Gradually progressive erectile difficulties, in particular, are well-established predictors of future cardiovascular disease, because the small penile arteries are affected by vascular disease earlier than the coronary arteries.”

“If you asked most people how they would define desire, it would often contain the word ‘spontaneous’, which is the version that is over-represented in our culture and mass media,” says Moyle. “In fact, the way desire shows up for many – and particularly those who are more familiar to each other, such as those in long-term relationships – is in a more responsive way. This means we [need to] go to it and create opportunities – if we wait for ‘the mood to strike’, it’s likely to be a long wait, as it has many life factors and other priorities to compete with.”

“It becomes about willingness to get turned on,” says Wright. “That’s about creating desire. To use a food analogy, how many times have you been full, not wanted to eat anything else, and then somebody puts a cheesecake in front of you and you suddenly fancy a slice? It’s about creating the scenarios where you, or your partner, are going to see the cheesecake.” Or indeed, whatever else they might find a bit tasty.