“There’s chemistry between us” is something we use automatically, often without thinking. It’s as if it were a metaphor to describe the spark, attraction or special tension between two people. Interestingly, however, in this case, the language is surprisingly accurate¹.
A modern cliché sums it up even more succinctly: “Love is chemistry, relationships are biology.”
Although this is a modern slogan from social media, from a scientific point of view, it contains more truth than might appear at first glance².
Infatuation, attraction and emotional bonds are not abstract phenomena. They are the result of specific chemical signals in the brain and body that have their own timing, dynamics and biological limits³. Valentine’s Day is therefore the ideal moment to look at love not as a mystical state, but as a fascinating biological process.
Is there such a thing as love at first sight? Or is it just a very quick reaction of the brain? From a scientific point of view, the first few seconds of an encounter trigger a combination of visual assessment, memory associations and neurochemical responses⁴. The brain evaluates facial symmetry, facial expressions, voice and scent, and compares them with stored patterns of attractiveness.
In the early stages of falling in love, dopamine plays a major role – a neurotransmitter associated with motivation, reward and feelings of pleasure. Increased levels of dopamine cause euphoria, heightened attention towards one person and a feeling that “the world is suddenly better”.⁴
Butterflies in the stomach have nothing to do with digestion. It is a reaction of the nervous system controlled by noradrenaline and adrenaline, which shifts attention and energy away from the digestive tract. The body prepares for a “significant event” – even if it is just a glance across the room.
I believe that so-called love at first sight is not a lie, but rather an accelerated version of biological evaluation that takes place before rational thinking has a chance to kick in.
In the early stages of falling in love, the dopamine system dominates. Dopamine increases feelings of energy, focus and anticipation. It is the same mechanism that underlies learning, motivation and the desire for rewards⁵.
Therefore:
• we think about one person repeatedly
• we feel increased
vitality • we ignore signs of fatigue or lack of sleep
Interestingly, serotonin levels may decrease during intense infatuation. Serotonin is a neurotransmitter associated with feelings of emotional well-being and stable mood⁶. Changes in serotonin levels during romantic love were described in the journal Psychological Medicine (1999), which showed that people in early relationships had different serotonin system values compared to the general population¹. This mechanism explains compulsive and repetitive thoughts about another person and the feeling that we simply cannot get them out of our heads.
It could be said, with a touch of irony, that a brain in love is a brain with temporarily reduced critical thinking. Evolutionarily, this makes sense – excessive rationality would hinder rather than promote reproduction.
If dopamine and serotonin are responsible for the initial stages of falling in love, oxytocin is responsible for building a relationship. This hormone is released during physical contact, hugs, touch, but also when we feel safe and trusted. It plays a key role in long-term bonding and maintaining relationships.
This fully confirms what we mentioned above – that relationships are biological. Maintaining closeness, cooperation and mutual tolerance is not just a matter of emotions, but also of hormonal regulation.
I note that disappointment often arises not because “love has disappeared”, but because its biological basis has changed, which we are not always able to recognise or accept⁵.
Although the role of pheromones in humans is still being studied, there is evidence that body odour plays a role in mate selection⁷. Studies suggest that people may subconsciously prefer the scent of individuals with different immune systems, which would increase the chances of healthy offspring from an evolutionary perspective⁷.
Interestingly, this mechanism operates outside of conscious evaluation – the “chemistry” between two people can arise before we are able to explain it rationally.
Some Valentine’s Day symbols also have a chemical background.
Chocolate contains small amounts of phenylethylamine and theobromine, substances that can slightly affect mood and induce a feeling of well-being⁸. Although their effect is weak, when combined with a sensory experience, they can contribute to a positive perception of the moment.
Alcohol lowers social inhibitions and increases dopamine release, but its effect is double-edged – short-term relaxation can quickly be replaced by fatigue or impaired decision-making⁸.
From an evolutionary perspective, falling in love is a temporary state. The brain is not designed to maintain high dopamine levels over the long term – it would be metabolically unsustainable⁵.
Gradually, a more stable neurochemical balance is established. This is where the difference between an acute chemical reaction and a long-term biological process becomes apparent.
A relationship requires adaptation and regulation of behaviour. If love remained only chemistry, it would be short-lived. If it is to last, it must also become biology.
A scientific view of love does not diminish its romanticism. Rather, it frees it from unrealistic expectations and shows how sophisticated the system behind the feelings we take for granted really is. Infatuation is intense but temporary. Bonding is more stable but less dramatic. Both phases have their place and significance.
Valentine’s Day can be an opportunity to look at love a little differently – in a more informed way. Understanding that love is a combination of biology, chemistry and conscious decisions gives it even greater value.
Ing. Mária Zajičková, PhD.
organic chemist, science populariser
1. Marazziti, D., Akiskal, H. S., Rossi, A., & Cassano, G. B. (1999). Alteration of the platelet serotonin transporter in romantic love. Psychological Medicine, 29(3), 741–745.
2. Fisher, H. E., Aron, A., Mashek, D., Li, H., & Brown, L. L. (2005). The anatomy of love: Neural systems for mate choice. Journal of Neurophysiology, 94(1), 327–337.
3. Aron, A., Fisher, H., Mashek, D. J., Strong, G., Li, H., & Brown, L. L. (2005). Reward, motivation, and emotion systems associated with early-stage romantic love. Neuroscience, 135(1), 217–226.
4. Marazziti, D., & Canale, D. (2006). Hormonal changes when falling in love. Journal of Affective Disorders, 92(2–3), 211–215.
5. Carter, C. S. (1998). Neuroendocrine perspectives on social attachment and love. Hormones and Behaviour, 34(3), 264–279.
6. Young, S. N. (2008). The neurobiology of human romantic obsession. Psychopharmacology, 199(3), 347–357.
7. Wedekind, C., Seebeck, T., Bettens, F., & Paepke, A. J. (1995). MHC-dependent mate preferences in humans. Nature, 378, 611–612.
8. Di Castelnuovo, A., Rotondo, S., Iacoviello, L., Donati, M. B., & De Gaetano, G. (2010). Food, mood and neurotransmitters. Nutrition Reviews, 68(7), 409–419.
Explanatory notes
Dopamine – a neurotransmitter associated with motivation, reward and feelings of pleasure
serotonin – a neurotransmitter associated with emotional well-being and stable mood
oxytocin – a hormone that promotes trust, bonding and long-term relationships
pheromones – chemical signals that can influence the behaviour of other individuals
