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.

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 and the caudate nucleus (Figure 1), 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

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

  1. Oxytocin…having a dog, does one’s hormone increase. Heard dogs are good
    For people who are depressed.

    1. yes friendship with an animal can have many of the same benefits as human friendships including oxytocin and bonding. please educate yourself to a dogs social and other needs before adopting because the pet has no choice in the matter so you have a higher duty to treat a pet apropriately and give it a decent life. please consider volunteering at a rescue or shelter before committing to adopting, you will learn so much and help so many animals and people and that helps depression too.

      1. Fostering is fantastic too. Since you are helping them out and have the option to adopt but if you know your living or work situation may cause you to move often its not going to ruin things for everyone.

    2. Notes for the author:

      Good but there is a missing term in the second sub-section of the attraction section.

  2. @Katherine Wu…Wow, what a nice article. What you say of the ‘liberation’ (freedom to think and act as self) as the fourth component in love with/without lust, attraction, and attachment? I don’t have a reference than me itself for now.

    1. Is there drugs out there, that can block these chemicals so that we can never be attracted & attached to a significant other, therefore we can never be hurt by love and stay content and happy as a single free human?

      1. A positive interaction between two (or more) humans with verbal and non-verbal cues triggers an orchestra comprising of chemical neurotransmitters and electrical synaptic discharges which results in a symphony which is unlikely to be replicated by the action of a soloist in the form of a single pill. Multiple psychotropic pills given in an attempt to produce similar effects often result in cacophonies leaving the mind in a state which is sometimes worse than the problem it tried to rectify. This may be due to drug interactions, side effects or withdrawal symptoms. This is not to say that medications for the mind are useless or harmful but that the human element is irreplaceable even when medications of proven value are administered.

        1. I can speak from personal experience about what George is saying. I was taking an ADD medication called Dexedrine. One of the effects of Dexedrine is that it boosts dopamine levels. It had lots of very harmful side-effects. Coincidentally this was around the same time that I was falling in love with someone, and I can tell you the experience was at least 10 times worse for everyone because of the medication.

      2. It wouldn’t be blocking the chemicals, it would be blocking the receptors of this chemicals. You block these receptors by providing them with chemicals outside the body’s self production. Drugs that can do that are antidepressants, and others like amphetamines. Of course there are always side effects, and withdrawal symptoms. So there is no way to continously block these receptors and be 100%, 24/7 happy.

  3. Since love Is caused by the chemicals dopamine, serotonin, norepinephrine and oxytocin you could say every time you fall in love it could be the beginning of a Chemical romance I’m sorry I couldn’t help it

  4. Hate to make everything political, BUT — both the infatuation /love discussion and dislike for those different from ourselves in this great article make me think seriously that it might explain some big problems we currently have in the White House. Has this been shared with appropriate circles in Washington? I pose this with all seriousness.

  5. I don’t believe this is all just chemicals. If that’s the case it would be a valid defense in court to just blame chemistry for everything.

    1. To be honest, humans probably do not even have free will. Our bodies have to obey the physical laws of the universe, but in order to predict what someone will do we have to know the starting conditions of almost everything. Because this truth alludes us, we explain it by saying we have free will, just like we explain miracles as phenomena. In reality, and court cases, while the chemical imballance standpoint could be argued, that would either be too out there to be valid, or it would be the same as arguing they were not mentally aware of their actions.

  6. Brilliant. Spent the day in a semi meltdown which led me to wonder if this was indeed the culprit. Explains it beautifully. Thank you.

  7. Loved your article………
    Hormones are synthesized in small amounts but leaves a great impact on individuals and society ………. seriously!!???

    1. I and my lover had been apart for 7 months until my sister told me about a spell caster who had helped her, She said the man was very powerful and that he could help me too. The name of this powerful man is Robinson buckler, after I contacted Robinson buckler in the next 48 hours my ex lover came back to me on his knees begging for my forgiveness and for me to accept him back. It was unbelievable as I was very surprised and happy I finally have him back after several attempts trying to get him back. Robinsonbuckler@ hotmail. com is too strong and contains no negative effect because it’s just like the love spell opened his eyes for him to see how much I truly love him.

  8. Does anyone know her contact information (preferably email)? I am doing a research paper on the science behind the feelings of love and I would love to interview her. Great article!

      1. Hi! I am also writing a research paper, would you mind sharing any of your sources with me? Maybe we can proof read each others work?

        1. Hello my fellow intellectuals! I am currently indulging in some adverse learning for an anatomy class as well. Would you be so kind as to share some sources to see if mine are credible enough? Oh and before I forget can I see how you guys formatted your paper to check if I’m doing it right?

  9. Just something to think about free will….
    Most physical objects’ trajectories are decided by initial conditions and forces which subsequently act on it as per physical laws..(quantum phenomena excluded)…
    To apply the same paradigm to human actions and thereby deny free will (or to state that free will is a misnomer for our inability to know initial conditions) is a leap of faith…
    Consider that human actions can be influenced (modified/initiated) by perceptions of the future (either true or false) and hence its equivalence to Newtonian physics is not quite appropriate at this stage of our ignorance……………
    In addition, the action of a person who knows she/he will be held responsible for the outcome of his/her actions as compared to someone who can “beat the rap” will differ…
    Some things to ponder before concluding our take on free will….

  10. Brilliantly done. I understand where those people are coming from stating “free will”, although, free will still applies to this. Attraction is not merely based on ones physical prefers. As such, although I may be physically attracted to someone that changes quickly at first site of an unattractive quality such as greed, bad temper, lack of intelligence, as well as intolerance. Free will is there. The biggest proof of that are those who abstain, such as myself. Its not that I am not attracted to anyone it is just that I willing ignore or redirect those desires. Free will is a major player in a healthy relationship of any type. To simply deny free will existence is to claim every one of us is the same and we all know that is biologically impossible i.e. even twin have differences.

    1. Yes I agree.

      I have been incredibly physically attracted to people I don’t find aesthetically attractive or to people whos personalities made me want to push them off a cliff.

      And my free will can make me abstain if i have to such as if it would be an inappropriate relationship as i may already be in one or because I am not on birth control and dont want to risk pregnancy for instance.

  11. I loved the article, I gotta say I found it arousing, must have been the serotonin and oxytocin in my brain? Ok, sorry, I just had to say it.

  12. Hi!
    I really like that article. Since i know a bit (a tiny bit) about brain chemistry, i’ve always seen love in a more chemical aspect. And your article allowed me to see everything clearer.
    For those out there who mention free will, couldn’t we say that the early stages of love (especially attraction) is only an impulse toward another human being, that eventually fades away (that could be why some pretend that love only lasts 3 years) and that afterwards the cortex with rational thinking takes over. Loving someone for rational reasons, eg “he is a great person” ” he takes care” “she is honest” etc..

  13. I loved the article but I would love if an explanation was given on how the brain is involved to regulate the three parts of love , attraction, lust, and attachment, I mean what is the controlling chemical for the free will?

  14. the pain of getting hit in the ankle with a razor scooter is so painful that its worse than a woman giving birth. imagine getting hit and ur foot getting cut off. its so painful. known from experience…

  15. The article was very informative and interesting. I spent 40+ years in the nursing profession as well as successful marriage and this is very intriguing to me. I would like to express the our creator did a beautiful job of intelligently designing humans. There are some good medications and therapies to help when things malfunction but sometimes I think we can mess things up by lack of understanding and interfering with the design of the human and nature.

    1. Intelligent design huh? That’s about as likely as a not so intelligent design if you ask me. we have nothing to compare our design to to determine how intelligently it was designed, maybe our creator was the last in his class and his creation (the universe and everything in it) was poorly designed compared to other creations of other creators, that’s why there was a couple million years and many different versions of early human before modern humans showed up and decided were part of an intelligent design. Maybe our creator gets laughed at by other creators because after 13.5 billion years his most intelleget primates are people, and people are only intelligent when compared to something else in this not so intelligently designed creation. We are smart enough to destroy their planet, smart enough to realize we are destroying our planet, but just to stupid (greedy) to care.

      1. While that is a perfectly stated shared opinion you might just find that the processes of this world are evidently exceptional in comparison to our own imaginations; some might not appreciate it but it would be interesting if they did.

        1. And also-I care about the planet, I’m just not the person that has the stress of caring for their countries needs and primary demands. People do things for specific reasons-no one is outright evil. (More or less anyway.)

  16. This assisted me in my understanding of the human body and psychological processes, I greatly appreciate this being created because it provides many of the answers I have been looking for. Good job. -Some high school freshie

  17. Is it possible for one person to love two people EXACTLY equal? Let’s say a guy has his wife and his daughter and he loves them both very much. I think it’s impossible to love them both equally, there will be a slight difference because the likeliness of chemical levels being exactly the same towards two separate people is highly unlikely. I am sure at times the chemical levels will fluctuate due to certain actions, which would only mean that if someone were to love two people equally it would only be for a very small amount of time because chemical reactions can only last for so long. The reason I ask this question is because my fiance got mad at me because I said I’d love our child just slightly more than her. Also, I said I’d choose my child over her in a life and death situation where I had to pick one or the other and I said that I hope that she’d do the same. She said that it is possible to love people equally and that it is not fair that my love would not be equal in the family. I just do not see how it is scientifically possible to love several people the same amount.

  18. An interesting read on the dynamic chemistry behind the phenomenon called “Love”.. However, it would have felt much more complete, had it dissected the chemistry behind more forms of love other than physical attraction & biological bonding/attachments. It would have been much more interesting to know the chemicals that come into play when we develop unconditional love based feelings like compassion, tenderness & empathy towards fellow human beings & animals/life forms when we realize that they are going through some form of suffering.

    And this is comment No.50, by the way 🙂

  19. That’s a great read for someone like who became curious enough TODAY to find out if science has figured out LOVE. This is after 21 years of being in a relationship and a science graduate 🙂

  20. I don’t understand the difference between lust and attraction.

    I’m not an expert and this seems counter intuitive to me but based on the little I’ve read (about different regions in the brain controlling sexual desire and love) I would lean (or am considering leaning) toward the idea that sexual attraction and love are two fundamentally unrelated mental states and ‘romantic love’ is just the combination of sexual attraction and love (and obsessiveness if we’re talking about infatuation but obsessiveness wouldn’t make it a distinct emotion – you can obsessively hate someone, be obsessively interested in someone or obsessively love or admire them without physical attraction). Beyond that I think ‘romance’ is a cultural idea. A whole is not more than the sum of it’s parts, it is the sum of it’s parts. I don’t think there are different kinds of love – people have different kinds of relationships with different kinds of people and they express the affection they feel for them in different ways. It still seems to me that there’s an inherent psychological component to sexual attraction and intimacy, I don’t know if that’s compatible with the idea that sexual (or even sensual) desire and love are inherently unrelated. I still think that affection and emotional intimacy are a consequence of sexual attraction and sexual intimacy for animals who are capable of affection.

    In general I think a lot of the pop science you find online is biased, intellectually dishonest (riddled with half truths presented out of context or logically flawed interpretation of data etc.) or misleading.

  21. Really at last i knew about love, its so crazy that love is also an chemicals, but thanks a lot for giving me knowledge about love .

  22. What a great article on the understanding the basic chemistry of “love” ; thank you! I think this is why it is true that you can fall “in love” with anyone, all the basic chemistry elements are there in our body. You may not want to or choose to, but, it is possible. However, there are deeper bonds that have finer elements that are missing in the article. There is a spiritual element to love that draws us to each other that has to do with a fundamental energy in our bodies that may be difficult to measure directly. I believe this finer matter is what accounts for people doing things for love that are “superhuman”, that supersede our chemical signals or elementally driven desires. This spiritual component is one that usually develops over time and can becomes a bond that is so strong that it defies metrics and yet we feel it almost as tangible as a tie that binds. We can not truly understand love without the spiritual components.

  23. Good work .I wonder what of unrequited love .A constant flow of unrewarded loved up chemicals with no real check to their balance .No intimate relationship problems , hurdles to numb the flow .

  24. There are also infinite other issues affecting your love choices aside from hormones such as how much your parents showed affection, whether your family had a father figure, on and on. Obviously hormones are involved and they’re the same ones that cause drug addiction. I can’t believe someone asked whether there was a way to control dopamine level enough to block basic human emotions. This is basic neurobiology. The comments on here are absolutely unreal.

  25. I told a friend of mine that I had an intuition to her loss of appetite and this is it. I hope she reads this comment. 😁😁

Leave a Reply

Your email address will not be published. Required fields are marked *