You know that feeling when you meet someone, and you just vibe? You never run out of things to talk about, you laugh together, you have tons in common, and you feel a sort of magnetic-like attraction to them? That, our friends, is called chemistry. It’s great, isn’t it? 
You can also hear people say, “there just wasn’t any chemistry” to explain why their first date won’t turn into a second.
So what is chemistry, really? What does it mean to have chemistry with someone?
A whole set of hormones and complex physiological interactions that make chemistry a little wonder of the world. It turns out the science behind love is both simpler and more complicated than we might think.
So, if there’s really a “formula” for love, what is it, and what does it mean? Where does love reside? What triggers it? And what’s really going on in our minds and bodies when we fall “head over heels”?
When it comes to love, we are at the mercy of our biochemistry. Romantic love can be broken down into three categories: lust, attraction, and attachment – each stage aided by a different set of hormones.

The idea of “love at first sight” might be more accurately described as lust at first sight. Appearance is one of the most prevalent catalysts for chemistry. Good looks can arouse desire in almost anyone. Our cultural conditioning instills these values, so we respond unconsciously to others on the basis of how they look. When under the spell of sexiness, we don’t realize that physical attraction is what’s driving our interest and instead identify it as the ever-elusive chemistry.

Attraction appears to be a distinct, though closely related, phenomenon. While we can certainly lust for someone we are attracted to, and vice versa, they can occur independently of one another. Attraction involves the brain pathways that control “reward” behaviour, which partly explains why the beginning of a romantic relationship can feel so exhilarating. People “in love” experience a range of intense feelings, such as intrusive thoughts, emotional dependency and increased energy, especially in the early phases of the relationship.
Brain activation in response to a romantic partner both rewards social interaction and impedes negative responses. How much the brain is activated during the early stages of a romantic relationship seems to influence both our own well-being and the extent to which the relationship is a success or failure. It’s the difference between using the brain in our heads vs the “brain” in our pants from the lust phase.

Produced by the hypothalamus, it is a particularly well-publicised player in the brain’s reward pathway – it’s released when we do things that feel good to us. In this case, these things include spending time with loved ones and having sex. High levels of dopamine and a related hormone, norepinephrine, are released during attraction. These chemicals make us giddy, energetic, and euphoric, even leading to decreased appetite and insomnia – which means you actually can be so “in love” that you can’t eat and can’t sleep. In fact, norepinephrine, also known as noradrenalin, may sound familiar because it plays a large role in the fight or flight response, which kicks into high gear when we’re stressed and keeps us alert. Brain scans of people in love have actually shown that the primary “reward” centres of the brain fire like crazy when people are shown a photo of someone they are intensely attracted to, compared to when they are shown someone they feel neutral towards (like a work colleague or an old high school acquaintance).

Attachment is the predominant factor in long-term relationships. While lust and attraction are pretty much exclusive to romantic relationships, attachment mediates friendships, parent-infant bonding, social cordiality, and many other intimacies as well. Romantic love appears to be universal, but the extent to which romantic or sexual love forms an important part of long-term relationships may vary.  
The two primary hormones here appear to be oxytocin and vasopressin, the hormones most closely associated with romantic love. Oxytocin is often nicknamed “cuddle hormone” for this reason. Like dopamine, oxytocin is produced by the hypothalamus and released by the pituitary gland in large quantities during sex, breastfeeding, and childbirth. This may seem like a very strange assortment of activities – not all of which are necessarily enjoyable – but the common factor here is that all of these events are precursors to bonding. 
Together, these findings highlight the manner in which hormone activity may help or hinder the formation of a close relationship.

And finally, what would love be without embarrassment? Sexual arousal, but not necessarily attachment, appears to turn off regions in our brain that regulate critical thinking, self-awareness, and rational behaviour, including parts of the prefrontal cortex. In a nutshell, love makes us dumb and makes us do stupid things we often regret.
Tip: Make sure you know the difference between love and lust. Enjoy the physical attraction but don’t move ahead too fast. Take time to assess what else is on offer. With time, the allure of a purely physical attraction will wear off, and you will be able to see the whole person more clearly.
love truly is a kind of drug!