It happened in an instant: our eyes met across the dance floor and we moved towards one another. Something pulled us closer together. “What’s your name?” I asked with the confidence of a 24-year-old who had zero expectations of meeting anyone, let alone a romantic partner, at a rave party at 3am on New Year’s Day. “Nick,” he replied. “What’s yours?”

It was his eyes and then his smile that drew my body closer to his. We danced until the sun came up. Then we went our separate ways and, as with all great millennial romances, a friend request on social media followed. By April, we were Instagram-official. Had the universe been turning its gears, preparing us both for that moment on the dance floor? Did the stars finally align? Perhaps it was simply pot luck. All I know is that seven years later, we’re to be married and, yes, we are very much in love.

My experience is far from unique. Poetry, novels, music – all kinds of art – have popularised the phenomenon of love at first sight for centuries. But what is it, how do we measure it? Does it even exist? What happened on the dance floor that night? And was a romantic relationship inevitable?

What is love at first sight?

One hundred milliseconds – that’s precisely how long it takes to evaluate a potential sexual partner. And if, after that split second, you deem that person to be attractive, emotions will begin to kick in as well as some animal-like instincts.

Anthropologist Helen Fisher explored the process of communicating our attraction to another person via a copulative gaze in her book Anatomy of Love, first published in 1992.

“The gaze is probably the most striking human courting ploy,” Fisher writes. In cultures where eye contact between the sexes is permitted, “men and women often stare intently at potential mates for about two to three seconds during which their pupils may dilate – a sign of extreme interest. Then the starer drops his or her eyelids and looks away.”

So, what is it that makes our pupils dilate? What is it that triggers a snap judgement that could lead to a romantic connection?

Unsurprisingly, looks matter. Studies reveal we are sexually attracted to people who look like us. In 1999, researchers asked subjects to rate pictures of faces morphed with their own and found the subjects each rated the morphed faces as being more attractive.

Other physical traits can also seal the deal: “Men and women around the world are attracted to those with good complexions. Everywhere people are drawn to partners whom they regard as clean. And men, in most places, generally prefer plump, wide-hipped women to slim ones,” Fisher writes.

The medial prefrontal cortex, near the front of the brain, is responsible for such judgements. Researchers in Dublin discovered that one particular area of this region – the rostromedial prefrontal cortex, a segment located lower in the brain – goes one step further in evaluating physical attractiveness by asking, “Is this person a good match for me?” This is the same brain region known to be important in social decisions, particularly how similar someone is to you, the study’s authors explained.

Essentially, we are evaluating someone’s attractiveness in those initial milliseconds while also determining their compatibility. But it’s all very unromantic, really, says Trish Purnell-Webb, a clinical psychologist at the Relationship Institute Australasia.

“When we’re looking to mate, the brain will constantly search the environment and look for another person who will be a good mate and make strong babies,” she says.

You like what you see, so what happens next?

There is a surge in the attachment hormone oxytocin, says Purnell-Webb. Oxytocin stimulates the secretion of other neurotransmitters – molecules that act as chemical messengers – such as dopamine, which fires up the brain’s reward centres. At this point, you begin to focus more intently on that person, and there will be a spark of interest in your eyes.

“Imagine a dog pricking up its ears when it senses its master has returned home – that’s what a person who is experiencing attraction is like,” says Purnell-Webb, adding that generally it’s subtler than with dogs, although not always.

Often called the “cuddle hormone”, oxytocin compels us to get close; when we are feeling close to somebody else, we secrete more of it.

“Oxytocin is actually the hormone for poor decision-making,” says Purnell-Webb. “It makes you become a bit obsessed and compulsive. You’re being driven to try and make contact and attract the same interest back.”

The more signs you get from the other person that they are interested in you, the more oxytocin is released. It’s during this time that we often feel like our heart is racing, our palms get sweaty or we have butterflies in our tummy, says Gery Karantzas, the director of Deakin University’s Science of Adult Relationships Laboratory.

“It’s why we often hear love being referred to as a drug,” says Karantzas.

It’s a virtuous circle and a delicious cycle. “You develop these strong feelings for someone, particular parts of your brain get activated when you spend time with them, you therefore want to spend more time with them, which then releases more of these chemicals, and you feel more of those feelings and so on.”

Similar brain areas fire up if you take cocaine, as Fisher discovered in a groundbreaking experiment. She did MRI scans on 37 people who were madly in love, which showed a surge of activity in brain areas rich in dopamine. “But romantic love is much more than a cocaine high – at least you come down from cocaine,” Fisher said in a 2014 talk. “Romantic love is an obsession, it possesses you. You lose your sense of self.” You can’t, she adds, stop thinking about that other human being.

What’s love at first sniff?

Pheromones – which are, essentially, scented chemicals that act like hormones outside the body – allow us to literally sniff out a potential match. Think of them as a primal form of communication; smell plays a major role in sexual attraction and can even trigger ovulation. But here’s the thing: pheromones smell different to different people.

“Male pheromones are often described as having a woody or musky smell while female pheromones smell more floral or sweet,” says Purnell-Webb.

At other times, depending on who is sniffing whose pheromones, they can smell bitter, sweaty or like stale urine. Some studies have suggested that, during ovulation, women are highly sensitive to the musk-like pheromones that men secrete.

As you continue to smell the other person, attraction builds, and you move closer to them.

Are you looking for anything in particular? Not really. It’s more a case of beauty being in the eye of the beholder, says Purnell-Webb. “We all have particular personal preferences, some people like beans, others peas,” she says. There is some evidence to suggest attraction is part of our genetic imperative – our genes determine who and what we are attracted to – which raises the question, is there a perfect match out there for each of us?

That’s the premise of the Netflix show The One, set “five minutes into the future”, in which finding a soulmate is as simple as snipping off a strand of hair and posting it to a DNA matchmaking company. Because the company claims to find perfect matches on a genetic level, attraction is inevitable, actually involuntary. Upon first meeting, the match smells right, looks right and demonstrates all the right characteristics. They also taste good.

A 2000 study by Swiss biological researcher Claus Wedekind found that when humans kiss they exchange a wealth of biological and genetic information.

Women tend to be more attracted to men whose MHC (major histocompatibility complex) genes, which are essential to the immune system, are different from their own. Having different genes produces offspring with stronger immune systems.

Wedekind is best known for his 1995 “sweaty T-shirt study”, which asked women to sniff T-shirts that had been worn for two days by male students using no deodorant. The results showed they preferred the odour of men with different MHC genes to their own.

No one has conducted a T-shirt-sniffing exercise to examine how same-sex participants are magnetised towards some people but not others. However, the findings of a large genetic study into the underpinnings of same-sex attraction was released in 2018. It had researchers identify four regions in participants’ genomes that influence a person’s choice in sexual partner. Two were observed in men and women, and two were seen in men alone. The DNA identified could account for only 8 to 12 per cent of the genetics behind non-heterosexual behaviour. One of the variants was linked to the olfactory receptor.

Sniffing unwashed T-shirts is the human equivalent of dogs sniffing each other’s sweat glands (which happen to be located in their rear ends), says Purnell-Webb. Romantic, no? And kissing, for its part, may well be the most glamorised exchange of chemical information known to humans. This also explains why some people are immediately turned off after the first whiff (or kiss) while, for others, the intensity of attraction and desire only grows.

Can you engineer love at first sight?

Researchers of romantic love will tell you there are some definitions of love that would allow for the possibility of love at first sight, while other definitions leave no such room.

If we think of love as a purely physiological experience, then love at first sight is possible, says Mandy Len Catron, author of How to Fall in Love with Anyone.

“If we looked at what’s happening in your brain when you are feeling an intense attraction to a complete stranger, we’d see dopamine and norepinephrine levels rise, and we could definitely say you are having a love experience,” she says.

Of course, this definition has several implications. For one, it potentially removes personal responsibility from the act of falling in love. You’re simply going along for the ride and then – bam! – destiny steps in and offers up your one true love.

But if we were to think about love from a sociological or philosophical perspective, Catron says it becomes less about a feeling in our bodies that happens to us, and more about an action we choose. In this case, love is a verb – and even if we’re attracted to someone, we can still decide they’re not for us, for a whole range of reasons. By this reading, love requires work and doesn’t always fit so rosily in the love-at-first-sight wonderland, where individual effort is void and soulmates are served on silver platters.

Still, we gleefully consume and re-tell stories of being instantly struck with love, each tale another hit of ecstasy that fortifies the possibility that one day we might find extraordinary love.

“I understand why love at first sight is appealing,” says Catron, whose 2015 essay for the New York Times′ Modern Love column, titled To Fall in Love with Anyone, Do This catapulted a 20-year-old experiment into the cultural lexicon. The 1997 study, by US psychologist Arthur Aron, succeeded in making two strangers fall in love in a laboratory by having them answer a series of 36 personal questions face to face – What would constitute a “perfect” day for you? For what in life do you feel most grateful?, etc – and then had them stare into each other’s eyes for four minutes.

Six months later, the two strangers were married.

Catron, who came across Aron’s work while at university, decided to apply his technique in her own life, with an acquaintance. Naturally, they weren’t in a laboratory but a bar, and they weren’t strangers. Nevertheless, it worked.

Three months later they were still together, and Catron did what any writer would do: she wrote an essay about it. Published just as dating apps, such as Tinder, were sweeping the northern hemisphere, the piece offered something powerful, recalls Catron: a “ready formula for falling in love” that contradicted the idea of love at first sight, that love was something that simply happened to you.

After all, Catron chose to do the experiment; the acquaintance agreed. It was through these actions – and perhaps Aron’s carefully selected questions – that they achieved and sustained intimacy.

Speaking on the phone from her home in Vancouver in 2021, Catron says she is still in a relationship with that university acquaintance from her experiment six years ago.

Meanwhile, the fondness for the idea of love at first sight remains largely unchanged across cultures. In arranged marriages, for example, couples report similar feelings, only it is present during the marriage as opposed to the courting period.

“The reality is that, by nature, humans are very interested in story,” says Catron. “We have evolved to be narrative creatures and when it comes to romantic love we really like the idea that there is a soulmate or that there is someone out there who we are favoured to be with.”

There are countless examples – both fictional and real life – that have been associated with the notion of love at first sight. In Disney’s Sleeping Beauty, Princess Aurora meets Prince Phillip for the first time on her 16th birthday, and they instantly fall in love. In William Shakespeare’s Romeo and Juliet, the star-crossed lovers first lay eyes on each other at a ball – neither of them speak – yet after learning of Juliet’s name from a waiter, Romeo becomes infatuated, immediately declaring he has never been in love until this moment!

It’s all very quick and erratic. And it’s not just Shakespeare; Kylie Minogue’s 2001 hit Love at First Sight tells the same story, as do countless other pop tunes.

Can you make love at first sight feelings last longer?

According to Purnell-Webb, between nine and 12 months is the limit before the butterflies calm down. That’s the amount of the time it takes for a female to become pregnant and for the foetus to have developed to a point where she is likely to have a live birth.

“It’s all about keeping the human race going,” she reminds us.

But Karantzas says passionate love ebbs and flows in a relationship over time.

“We see an increase in other types of love as relationships go along,” he says.

Companionate love, for example, where having a deep sense of caring and concern for someone, often grows with a relationship. And when you register someone as your “lifelong love” the moment you see them, only time can tell whether you’re right or not.

“People will say, ‘Well, I knew instantly that I loved this person’. But often the people who are saying that are those who have been together five, 10, 15, 20 years,” Karantzas says.

Purnell-Webb says, “attraction is what happens, Hollywood romanticists have labelled attraction ‘love at first sight’, but it doesn’t really exist, love only develops over time.”

Catron prefers to align her ideas about love with writer Bell Hooks’ definition – that is, love is an action, never simply a feeling.

“It’s not about how you feel, it’s about what you do with those feelings and how you connect to another person and how we treat each other,” she says.

“By defining love as an action, we are more likely to have healthier, more loving relationships that are sustainable.”

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