Research has shown people do tend to decide whether they are romantically interested in a person within seconds of meeting them, and that near-instantaneous decision depends on a mix of physical and psychological cues they pick up about the person at a first glance.

As for actually falling in love, a set of researchers set out in 2017 to study love at first sight as soon as it happened. They staged meetings with potential romantic partners for some 400 men and women and then asked about the feelings they experienced during the encounter. A small number of people did report falling in love at first sight, but those feelings didn’t include high passion, intimacy, or commitment—all the classic hallmarks of romantic love psychologists look for, according to Sternberg’s triangular theory of love.

The main factor that predicted falling in love at first sight with a stranger? Physical attraction.

In fact, rating a person one point higher in attractiveness was associated with a nine times higher likelihood of reporting love at first sight. That suggests a great majority of people who claim to have fallen in love at first sight are actually experiencing lust at first sight.

To be fair, love and lust are very commonly confused, according to psychologists Simone Humphrey, PsyD, and Signe Simon, Ph.D. “The two phenomena activate similar neural pathways in the brain that are involved in view of the self, goal-directed behavior, happiness, reward, and addiction,” they write at mbg.

The intense, all-consuming feelings of passion, exhilaration, and longing associated with falling in love are the product of a series of neurochemical reactions in which the brain’s reward system, fueled by the neurotransmitter dopamine, motivates the person to seek closeness and intimacy with the object of their affection—similar to the way the brain behaves when a person is experiencing drug addiction. Research by behavioral anthropologist Helen Fisher, Ph.D., suggests this romantic drive response system can theoretically be triggered instantaneously.

That said, other research has found differences in the brains of people who’ve recently fell in love compared with those who’ve been in love for decades. While the brain’s reward systems lit up for both groups of people when thinking of their beloved, the newly-in-love couples had some additional parts of the brain activated: the ones associated with fear and anxiety.