by Katherine Wu
figures by Tito Adhikary

In 1993, Haddaway asked the world, “What is Love?” I’m not sure if he ever got his answer – but today, you can have yours.

https://www.youtube.com/watch?v=HEXWRTEbj1I?&autoplay=1

Sort of.

Scientists in fields ranging from anthropology to neuroscience have been asking this same question (albeit less eloquently) for decades. It turns out the science behind love is both simpler and more complex than we might think.

Google the phrase “biology of love” and you’ll get answers that run the gamut of accuracy. Needless to say, the scientific basis of love is often sensationalized, and as with most science, we don’t know enough to draw firm conclusions about every piece of the puzzle. What we do know, however, is that much of love can be explained by chemistry. So, if there’s really a “formula” for love, what is it, and what does it mean?

Total Eclipse of the Brain

Think of the last time you ran into someone you find attractive. You may have stammered, your palms may have sweated; you may have said something incredibly asinine and tripped spectacularly while trying to saunter away (or is that just me?). And chances are, your heart was thudding in your chest. It’s no surprise that, for centuries, people thought love (and most other emotions, for that matter) arose from the heart. As it turns out, love is all about the brain – which, in turn, makes the rest of your body go haywire.

According to a team of scientists led by Dr. Helen Fisher at Rutgers, romantic love can be broken down into three categories: lust, attraction, and attachment. Each category is characterized by its own set of hormones stemming from the brain (Table 1).

Table 1: Love can be distilled into three categories: lust, attraction, and attachment. Though there are overlaps and subtleties to each, each type is characterized by its own set of hormones. Testosterone and estrogen drive lust; dopamine, norepinephrine, and serotonin create attraction; and oxytocin and vasopressin mediate attachment.
Table 1: Love can be distilled into three categories: lust, attraction, and attachment. Though there are overlaps and subtleties to each, each type is characterized by its own set of hormones. Testosterone and estrogen drive lust; dopamine, norepinephrine, and serotonin create attraction; and oxytocin and vasopressin mediate attachment.

Let’s Get Chemical

Lust is driven by the desire for sexual gratification. The evolutionary basis for this stems from our need to reproduce, a need shared among all living things. Through reproduction, organisms pass on their genes, and thus contribute to the perpetuation of their species.

The hypothalamus of the brain plays a big role in this, stimulating the production of the sex hormones testosterone and estrogen from the testes and ovaries (Figure 1). While these chemicals are often stereotyped as being “male” and “female,” respectively, both play a role in men and women. As it turns out, testosterone increases libido in just about everyone. The effects are less pronounced with estrogen, but some women report being more sexually motivated around the time they ovulate, when estrogen levels are highest.

Figure 1
Figure 1: A: The testes and ovaries secrete the sex hormones testosterone and estrogen, driving sexual desire. B and C: Dopamine, oxytocin, and vasopressin are all made in the hypothalamus, a region of the brain that controls many vital functions as well as emotion. D: Several of the regions of the brain that affect love. Lust and attraction shut off the prefrontal cortex of the brain, which includes rational behavior.

Love is its Own Reward

Meanwhile, attraction seems to be a distinct, though closely related, phenomenon. While we can certainly lust for someone we are attracted to, and vice versa, one can happen without the other. Attraction involves the brain pathways that control “reward” behavior (Figure 1), which partly explains why the first few weeks or months of a relationship can be so exhilarating and even all-consuming.

Dopamine, produced by the hypothalamus, is a particularly well-publicized 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” centers of the brain, including the ventral tegmental area and the caudate nucleus, 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 an old high school acquaintance).

Finally, attraction seems to lead to a reduction in serotonin, a hormone that’s known to be involved in appetite and mood. Interestingly, people who suffer from obsessive-compulsive disorder also have low levels of serotonin, leading scientists to speculate that this is what underlies the overpowering infatuation that characterizes the beginning stages of love.

The Friend Zone

Last but not least, attachment is the predominant factor in long-term relationships. While lust and attraction are pretty much exclusive to romantic entanglements, attachment mediates friendships, parent-infant bonding, social cordiality, and many other intimacies as well. The two primary hormones here appear to be oxytocin and vasopressin (Figure 1).

Oxytocin is often nicknamed “cuddle hormone” for this reason. Like dopamine, oxytocin is produced by the hypothalamus and released 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. It also makes it pretty clear why having separate areas for attachment, lust, and attraction is important: we are attached to our immediate family, but those other emotions have no business there (and let’s just say people who have muddled this up don’t have the best track record).

Love Hurts

This all paints quite the rosy picture of love: hormones are released, making us feel good, rewarded, and close to our romantic partners. But that can’t be the whole story: love is often accompanied by jealousy, erratic behavior, and irrationality, along with a host of other less-than-positive emotions and moods. It seems that our friendly cohort of hormones is also responsible for the downsides of love.

Dopamine, for instance, is the hormone responsible for the vast majority of the brain’s reward pathway – and that means controlling both the good and the bad. We experience surges of dopamine for our virtues and our vices. In fact, the dopamine pathway is particularly well studied when it comes to addiction. The same regions that light up when we’re feeling attraction light up when drug addicts take cocaine and when we binge eat sweets. For example, cocaine maintains dopamine signaling for much longer than usual, leading to a temporary “high.” In a way, attraction is much like an addiction to another human being. Similarly, the same brain regions light up when we become addicted to material goods as when we become emotionally dependent on our partners (Figure 2). And addicts going into withdrawal are not unlike love-struck people craving the company of someone they cannot see.

Figure 2: Dopamine, which runs the reward pathways in our brain, is great in moderate doses, helping us enjoy food, exciting events, and relationships. However, we can push the dopamine pathway too far when we become addicted to food or drugs. Similarly, too much dopamine in a relationship can underlie unhealthy emotional dependence on our partners. And while healthy levels of oxytocin help us bond and feel warm and fuzzy towards our companions, elevated oxytocin can also fuel prejudice.

The story is somewhat similar for oxytocin: too much of a good thing can be bad. Recent studies on party drugs such as MDMA and GHB shows that oxytocin may be the hormone behind the feel-good, sociable effects these chemicals produce. These positive feelings are taken to an extreme in this case, causing the user to dissociate from his or her environment and act wildly and recklessly. Furthermore, oxytocin’s role as a “bonding” hormone appears to help reinforce the positive feelings we already feel towards the people we love. That is, as we become more attached to our families, friends, and significant others, oxytocin is working in the background, reminding us why we like these people and increasing our affection for them. While this may be a good things for monogamy, such associations are not always positive. For example, oxytocin has also been suggested to play a role in ethnocentrism, increasing our love for people in our already-established cultural groups and making those unlike us seem more foreign (Figure 2). Thus, like dopamine, oxytocin can be a bit of a double-edged sword.

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 behavior, including parts of the prefrontal cortex (Figure 2). In short, love makes us dumb. Have you ever done something when you were in love that you later regretted? Maybe not. I’d ask a certain star-crossed Shakespearean couple, but it’s a little late for them.

So, in short, there is sort of a “formula” for love. However, it’s a work in progress, and there are many questions left unanswered. And, as we’ve realized by now, it’s not just the hormone side of the equation that’s complicated. Love can be both the best and worst thing for you – it can be the thing that gets us up in the morning, or what makes us never want to wake up again. I’m not sure I could define “love” for you if I kept you here for another ten thousand pages.

In the end, everyone is capable of defining love for themselves. And, for better or for worse, if it’s all hormones, maybe each of us can have “chemistry” with just about anyone. But whether or not it goes further is still up to the rest of you.

Happy Valentine’s Day!

Katherine Wu is a third-year graduate student at Harvard University. She loves science with all of her brain.

Further Reading

  1. For a long-form human interest story on love, see National Geographic’s coverage of “True Love”
  2. For a very in-depth (and well-done!) introduction to the brain and its many, many chemicals, check out the NIH’s Brain Basics page
  3. For the New York Times’ take on falling in love with anyone, ask these 36 questions

238 thoughts on “Love, Actually: The science behind lust, attraction, and companionship

  1. Infatuation, rather than love, is interesting, it seems to seriously impair and disable the person with it and is so intense and irrational it usually puts off the the person you are infatuated with. You wonder why it exists it is so dysfunctional, is it a relic from earlier stages of evolution that doesn’t really fit in civilization ?

  2. A good read.
    I see the progression a little differently. Could lust as a desire trigger first the attraction, leading to affection, culminating in attachment?

  3. Love is a huge and mean while a simple topic.
    Love is the beautiful feeling that almost every living thing has. And, it depends how they express that feeling.
    Love does not only mean sexual feelings or attraction.

    Love is Love!
    It is what it is!
    So keep loving yourself and everything else that is not harming us and this beautiful world.

  4. Attraction involves the brain pathways that control “reward” behavior. That’s why relationships on first weeks or months can be so at-touched because of the attractiveness of your partner, I mean it is in most relationships ( love is its own reward

  5. I love this article, neuroscience is fascinating and explains a lot! Also as a bisexual person, knowing how it works makes it kind of make more sense, like my brain just doesn’t filter out the women. For some weird reason, the neuroscience explanation explains queer identities better to me in my head.

    Also, an opinion I have is that love is partially a social construct too. Like the basic feelings are undoubtedly brain chemistry, but the more specific things could be just how we were raised to believe it should be done?

    1. I have a feeling for someone and I think I does not love me but I really love me and it really hurts me sometimes I just want to forget about him but I don’t want to let go am just sad

    2. I like your view on the subject. I’ve been reading peoples comments on this article and some propose a meta-physical explanation for love. You seem to accept the scientific based explanation, while also bringing up the question about socialization and culture in the formation of the concept. I guess through time artists and religious tried to deal with feelings while it was impossible to comprehend it in biochemical terms, thus creating lore that can affect other people as time passes.

  6. I remember when starting both of my past antidepressants that when i started taking them and the brain starts to “adapt” and the serotonin level starts going bonkers that i experienced “love at first sight” all the time, on and off. Even if it was very mild i can surely connect it with the medication. I have mild OCD also so my serotonin is low by default and i personally can connect THAT with an increased tendency towards experiencing short lived temporary “love at first sights”. But because they are not really “genuine” they tend to go away just as fast as they appeared.
    Then another scary bit about antidepressants(SSRI/SNRI) is that if you ARE in love and starts taking those medications you can actually “Fall out of love” for real and there is quite a bit information out there on this phenomena.
    Another interesting thing is that Wolves lacking a specific gene that affects Vasopressin made them much more likely to leave their offspring in search of a new female to just repeat the process with(Maybe we can check peoples blood in the future to see if they are likely to leave their kids for new kids to leave) .
    But don’t be scared to start taking such medication if you really need it because depression can absolutely make you “numb” and “fall out” in the same way.
    It is quite scary and sad really how much we are affected by our brain-chemistry, from aggression,empathy,compassion to fear and joy.
    Just wanted to share these interesting experiences and facts.
    / Daniel

  7. I think the mention of OCD is interesting because my partner has it, I didn’t know he had lower seritonin levels. And the ethnocentrism comment, though out of the blue, was also interesting because I just finished an Anthropology class.

    1. There are plenty of people with dogs and get sex on a regular basis and are still depressed. If only the world was that simple.

  8. It doesn’t take a matchmaker to see where this is going: Increasing levels of dopamine = euphoria and desire = greater attraction to the one we love !

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