Scientist Luke O’Neill says being in love is as addictive as heroin, lighting up the same parts of the brain.
The professor of biochemistry says lovers go on such a high that it feels like being on drugs.
In fact, synthetic drugs were created to mimic the euphoria of romance and passion.
It’s all required for bonding to ensure the survival of the human race, explained Prof O’Neill.
He told the Irish Mirror about the science of falling in love, as we celebrate St Valentine’s Day.
Luke said: “There are a few key chemicals rushing around in the early stages of romantic love. Oxytocin plays a big role, which is why it’s sometimes called the love hormone.
“It makes you feel as though you are possessed by your lover to the exclusion of everything else.
“It’s designed to make you get on with them. It’s biology in action.
“Noradrenaline is another one - that’s the one that is key in attraction and makes you so excited you can’t sleep or eat.
“Dopamine is a key one - it’s misunderstood as being about pleasure, but it’s more about motivation.
“You do feel good, and it’s pleasurable, but the pleasure is about the motivation you feel with the other person.”
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He explained how infatuation is part of the process. “You start off having this massive infatuation and that’s essential to make sure you don’t get distracted.
“Back to biology, that’s to increase the chances of reproduction.
“The same parts of the brain light up as if you’re on heroin. It’s addictive behaviour - you will do anything to get access to that drug. It’s the same when you really fancy someone.
“You’ll stay late at loud parties you don’t really want to be at, or stick the awfulness of a nightclub, just to be with them.”
Addiction to artificial drugs is a chemical way to try and mimic the obsessive love feeling. ”It’s no coincidence they trigger a pathway into the brain normally triggered when you’re in love.”
However, he says being so lovey-dovey you’re out of your mind - like Prince Harry and Meghan Markle or Kourtney Kardashian and Travis Barker - cannot go on forever.
But the addictive power of love follows on into what’s called the “bonding” stage.
“If you were forever staring into each others’ eyes, we’d get nothing done and be at risk of being eaten by tigers.
“So you move onto this caring phase and you form this bond and you’re a team. We’re biological machines and we have honed all this over millions of years of evolution.
“We all know this stuff too, on a certain level. We are a very social species - we’re not loners.”
O’Neill explains it all in his current book What Makes Us Human, in the chapter The Science of Finding Love.
It provides the secret of what makes us attracted to one person and not the other.
One of the main elements is pheromones - secreted body chemicals that trigger a response in other humans.
Ever find the smell of someone intoxicating, and you don’t know why? It’s likely pheromones.
Said Luke: “Pheromones are a controversial thing, and we know they exist in other creatures.
“Insects secrete to attract a mate. When you hear dogs whining they are sensing pheromones in the air, and they are mammals, like us.”
“There is evidence that people secrete these things in sweat glands and are drawn to someone in some cases, or repelled by them in others.
“We seem to be smelling their immune system - whatever is in the sweat or pheromone is one indicator of their immune system
“What scientists have found is we like them to be somewhat similar to our own, but not too similar. Studies where people were asked to rate different smells they were attracted to show we want somewhere in the middle.
“We know this from the perfume industry that has spent centuries trying to recreate that smell.”
A surprise one is how women look at a man’s fingers - not to see if they’re wearing a wedding ring, but to determine their attractiveness.
“The finger’s length indicates levels of testosterone. The female would like a male with a certain level of testosterone, which means more muscle mass and the offspring as strong as possible.”
Even perceptions of beauty are based in science. “A symmetrical face is regarded as more beautiful and suggests strong genes. If you’re a bit asymmetrical you haven’t developed optimally and may be carrying less optimal genes.”
He says diversity is key for the immunity of a community, which means there is someone out there to suit everyone. “If we don’t have enough diversity we are all clones of ourselves which is not good for immunity.
“So some people don’t mind a crooked face and others don’t want that and that’s essential.
“If we were all attracted to the same person, it would be mayhem.”
Also, women are inclined to be drawn to people like their father, perhaps because it was the first face they saw. So we might like people who look a little bit like ourselves.
Some people are more prone to falling head over heels than others - but that’s a mixture of biology and psychology.
“It’s highly complicated and a mix of genetics and you’re upbringing, so it’s hard to judge. There is no doubt upbringing is a key feature in this response.”
But it tends to happen to all of us at some point, once we reach a certain age.
“We all remember puberty comes on and suddenly we’re getting crushes that were not there before. It’s designed for us to mate - it’s all about recreation and getting the egg fertilised.
“If we didn’t have this compulsion, the species would not continue.
“If you got over it too quickly, you wouldn’t be bothered to mate and reproduce. This absolute compulsion is simply nature.”
