Brain

They say sex starts in the brain, and it’s true. The blissful feelings are due to nerves from the body being linked to the brain’s pleasure centres, which MRI scans show light up strongly during intercourse. Regardless of gender, the brain during orgasm is said to look much like the grey matter of a person taking heroin, according to a study published in the Journal of Neuroscience.

It’s often said that sexual experiences begin in the mind, and scientific evidence supports this notion. During intercourse, nerves throughout the body connect with the brain’s pleasure centers, which MRI scans reveal to be highly active. Regardless of gender, a person’s brain during orgasm shows similarities to that of someone under the influence of heroin, as noted in a study published in the Journal of Neuroscience.

Research indicates that men and women exhibit slightly different brain responses during sex. Women, in particular, experience a greater shutdown of the brain’s fear and anxiety centers at climax compared to men. Notably, activity in the lateral orbitofrontal cortex, responsible for behavior regulation, decreases significantly in women, potentially allowing them to relax and enjoy the moment fully, facilitating orgasm.

Nose

Interestingly, women exhibit heightened brain activity in regions associated with emotion processing during sex, hinting that the experience is more emotionally charged for them. Conversely, men display increased activity in visual processing areas, suggesting that visual stimuli play a more significant role in their arousal compared to tactile sensations.

Sexual activity can also influence your sense of smell and even lead to nasal congestion. Post-intercourse, you might find yourself needing tissues, as a 2008 study published in the Journal of the Royal Society of Medicine explains. The same physiological response that triggers arousal can cause nasal tissues to swell, resulting in a runny nose or sneezing, a condition known as honeymoon rhinitis, which affects both genders.

Eyes

We’ve heard the term “bedroom eyes”, and it seems there really is some truth to it. That’s because it’s not just your genitals that respond when you are turned on. Your pupils, the dark centres of your eyes that allow in light, get bigger too. Researchers at America’s Cornell University found that when men and women were shown arousing images in 2012, their pupils also dilated, increasing in size up to four times. In adults, normal pupil size ranges from 2-4mm in diameter in bright light, but may go up to 8mm during sex.

Sex can affect your eyesight in other ways too, according to a report in the British Medical Journal, particularly if you’re a man. This is because males are more likely to hold their breath in the immediate run-up to orgasm, often in an attempt to delay it. This build-up of pressure can cause the delicate blood vessels in the eye to burst, leading to a small haemorrhage and temporary blurred sight.

Feet

In the run-up to orgasm, it’s not just our pelvic floors that start to contract. Muscles all over our bodies tense up too. One knock-on effect is that some people may also point or curl their toes. This is because orgasm triggers involuntary muscle contractions throughout the body, not just in the genitals. Another reason our toes may clench is “motor overflow”. In other words, your nervous system is so excited that other muscle groups get triggered too. The toes get triggered because the same spinal nerves that control the pelvic floor muscles also supply our legs and feet, sending messages to them to tense up as well.

Breasts

According to research by the American sex researchers, William Masters and Virginia Johnson in the 50s and 60s, a woman’s breast size may increase by as much as a quarter during arousal. This is due to a rush of blood to the breasts, causing them to get engorged and get firmer and fuller. They might also change colour. Research has found around 50-75% of women also get a sex flush – or pink colour – as the vessels close to the skin fill up with blood.

Nipples

At the same time as a woman’s breasts get bigger, the muscles beneath them tense up. Blood also flows to the areola, the area around the nipple, sometimes making it look darker. This increased blood flow causes the nipples to stand erect. Women also find their nipples far more sensitive than men do. A study in the Journal of Sexual Medicine in 2006 found that 81% of women say they are turned on by nipple and breast stimulation, compared with just 52% of men. As each partner’s temperature rises during sex and they start to sweat, the apocrine glands in the chest area – regardless of gender – release pheromones. While your partner may not consciously detect this scent, it can help bond you more closely.

Heart

Your heart rates will rise during sex – but not by as much as you might think. As tension mounts in the run-up to orgasm, both men’s and women’s breathing, and heart rates start to rise. But it’s a mistake to think you can skip your workout just because you’ve had sex. Research has found most of this heavy breathing and rapid heart rate is triggered by signals from the nervous system rather than because you’re getting lots of exercise.

Your heart rate will steadily rise as arousal builds, and then peak at orgasm, according to a 2022 review in the Archives of Sexual Behaviour. In males, the average heart rate during intercourse ranges from around 100 to 125 beats per minute, roughly the same as brisk walking or climbing stairs. However women’s hearts don’t beat as fast – on average their rates only rise to around 90 beats per minute, the same as a light intensity activity like slow walking or cleaning.

Vagina

While it’s well known that penises have to get bigger for sex to happen, it’s less well known that vaginas get bigger too, a process known as “tenting”. A woman’s vagina is normally around 7-8cm long – about the length of a tube of lip gloss. But during arousal, the muscles around the vagina and uterus lift upwards, stretching it to as much as 12cm. This isn’t just to make penetration more comfortable. This tightening also draws the cervix – the small muscular opening at the base of the womb – upwards, allowing more opportunity for the sperm to pass through to find the egg.

Testicles

It’s not just the penis that changes shape. A man’s testicles do too. Usually, the testicles hang slightly away from the body so they are 2-4C cooler than core temperature. This is because too much heat damages them. During sex, however, the testicles are drawn towards the body by the cremaster muscle, just above them. This means that sperm don’t have to travel as far to get to the end of the penis. At the same time, the testicles also become warmer and softer, before dropping down returning to normal after ejaculation, according to a 2007 study in the journal Urologia Internationalis.