Feeling Chemistry: The Science behind Valentine’s Day

According to almost every culture on earth, love is the most important thing we can experience. I’m sure you can find quotes from the Bible, Shakespeare, or Hallmark Cards that describe love much more eloquently than I can. But love, just like any other experience, can be explained by the chemical reactions in our bodies. With Valentine’s Day once again upon us, I’ve made a guide to the neurochemicals which drive us to do crazy, stupid things for the people we love.

Most biologists point to several different drives that cause people to experience love. These include sex drive, partner preference, and attachment. Chemicals activate these pathways and deactivate negative emotions. This two-fold power can motivate and exhilarate. Not only do people experience attraction, they also fear social judgement less when they experience love. It’s amazing to think that such an incredible emotion can boil down to a collection of carbon, oxygen, nitrogen, hydrogen, and sulfur.

All of the molecular structures below were obtained from molview.org.


Dopamine is released by the hypothalamus, a structure located deep in the brain that serves as a link between the nervous system and the endocrine system. Dopamine is a “feel good” chemical that is linked to the formation of relationships as well as sex. Similar activity occurs when cocaine is used. Dopamine is highly rewarding, and has been connected from everything from gambling to alcohol addiction. Dopamine is involved in a variety of pathways but is one of the most widely known “love molecules.”


An increase in dopamine is coupled to a decrease in serotonin. Serotonin is linked to appetite and mood. Its presence is found to be decreased in people who are in the early stages of romantic love and those with obsessive compulsive disorder. People who are infatuated will have a tunnel-like focus on their partner, much like someone with OCD.


Oxytocin is also released by the hypothalamus, and is stored in the pituitary gland. It is released into the blood during sex and activities such as breast feeding. Oxytocin is linked to attachment and bonding. The receptors for oxytocin are located in the brain stem, and are linked to both romantic and maternal love. Research in prairie voles suggests that the location of these receptors may be related to monogamy.


Vasopressin is closely correlated to oxytocin. Vasopressin is also produced by the hypothalamus and stored in the pituitary gland. In males, vasopressin is linked to social behavior, including aggression towards other males. This is the chemical that makes The Bachelorette so entertaining — it may make men compete over women. Vasopressin is active in learning and memory in a social context, and is a chemical which strengthens bonding and attachment.


Estrogen is the primary female sex hormone, so it is obviously implicated in romance. Estrogen has not been found to increase in those who are in love, but it is essential to the development of a sex drive. High levels of estrogen are important; low levels can lead to depression and moodiness, and high levels of estrogen can block serotonin uptake, further promoting attraction.


Testosterone, the male sex hormone, is highly related to increased feelings of attraction. It stimulates feelings of love, desire, and paternal care in males, leading to an increase in oxytocin. When females come into contact with male testosterone during intercourse, it can even heighten their oxytocin levels. Testosterone is strongly correlated to sex drive in males, but it also causes them to care deeply for their child and mate.


Norepinephrine, also known as noradrenaline, stimulates the production of adrenaline. It is produced in closely-packed brain cell neurons (called nuclei), most importantly in the locus coeruleus in the brain stem. Upregulating adrenaline makes our heart race and our palms sweat. It impacts large sections of our brain and gives us that “fight or flight” feeling. Norepinephrine increases joy and can make you lose your appetite. Sound familiar?

Love is one of the most complex human emotions, but its basis is in these neurochemicals. So when things are getting hot and heavy on Valentine’s Day, be sure to tell your partner all about the chemicals surging through their brain. To nerds, it’s a really big turn-on.

“How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?” — Albert Einstein

Happy Valentine’s Day!

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