The person in the grip of a new affair is not fully rational. Their brain is flooded with dopamine at levels comparable to cocaine use. Understanding the neuroscience explains — not excuses — why otherwise decent people make catastrophically self-destructive choices.
Dopamine is not the pleasure chemical — it is the wanting chemical. It does not reward you after you get something. It fires in anticipation of getting it. Dr. Kent Berridge (University of Michigan) demonstrated that the dopaminergic "wanting" system and the opioid "liking" system are neurologically distinct. You can desperately want something that does not actually make you happy.
New attraction floods the nucleus accumbens, caudate nucleus, and ventral tegmental area (VTA) with dopamine. fMRI studies by Dr. Helen Fisher showed that viewing a photo of a new love interest activates the same brain regions as cocaine administration — with comparable intensity. This state produces: obsessive thinking, reduced appetite, elevated energy, reduced need for sleep, and sharply impaired risk assessment.
The brain habituates to any consistent stimulus. This is hedonic adaptation — the same neurological process that makes your first bite of dessert extraordinary and your tenth unremarkable. In long-term relationships, the dopaminergic response to a partner naturally dampens. This is not a failure of love — it is an inescapable feature of how the brain conserves resources.
Neuroscientist Dr. Lucy Brown and Dr. Helen Fisher found in their longitudinal research that couples married 20+ years who reported still being "madly in love" showed significantly different brain activation patterns than early-stage couples — less dopamine/novelty activation and more oxytocin/calm-attachment activation. Long-term love is a different chemical state, not a lesser one. But the dopamine-hungry brain may experience the transition as loss.
New attraction also floods the body with norepinephrine — the same compound released in fight-or-flight. This produces: racing heart, heightened senses, flushed skin, and acute focus on the target. The physical sensations of new attraction are virtually identical to those of fear. The brain, in its messy economy, often conflates arousal states — which is why perceived danger and taboo amplify attraction.
In the brain state of new attraction, serotonin levels drop significantly. Dr. Donatella Marazziti (University of Pisa) measured serotonin levels in newly-in-love individuals and found them equivalent to levels in people with obsessive-compulsive disorder. This explains the intrusive, looping thoughts about the new person — the inability to stop thinking about them is neurologically structurally similar to OCD.
For people in long-term relationships where the dopamine system has long since stabilised, an outside attraction can feel like waking up. The world becomes vivid again. Food tastes better. Music feels more intense. They feel young. This is the dopamine flood — and it is profoundly seductive precisely because it contrasts so sharply with the comfortable numbness of settled life. The outside person did not create this. They triggered a neurochemical state the person was already primed for.
The prefrontal cortex — responsible for weighing consequences, moral reasoning, and long-term planning — is functionally suppressed during high-dopamine states. This is why people in affairs routinely take risks that would seem insane to their normal selves: text messages on shared devices, meetings in familiar places, financial tracks. The cost-benefit calculation is being performed by a brain with 40% of its executive function offline.
The intense dopamine phase of new attraction neurologically resolves within 12–24 months regardless of circumstances — including in affairs.
When the dopamine phase ends, many affair partners describe sudden clarity — horror at what they risked — as the brain's normal function returns.
Couples can deliberately trigger dopamine by introducing genuine novelty: new places, new physical experiences, new shared challenges.
A long-term partner is not competing with the affair person. They are competing with a brain state. The person never really saw the affair partner clearly.