The human eye often reveals internal states without a single word. One intriguing cue is the change in pupil size. Many people have observed that pupils tend to widen, or dilate, when someone is looking at a person they are attracted to or love. This involuntary shift is a complex physiological response linked to our deepest emotional and biological processes.
How Pupils Function
The pupil, the black circle in the eye’s center, is an opening in the iris. Its primary function is to regulate the amount of light that enters the eye, similar to a camera lens aperture. In dim light, the pupil dilates to allow more light in, enhancing vision, while in bright conditions, it constricts to limit light entry.
This adjustment is an involuntary process controlled by the autonomic nervous system (ANS). The ANS has two main branches: the sympathetic and parasympathetic nervous systems. The iris contains two sets of muscles responsible for these changes: the iris dilator muscle and the iris sphincter muscle.
The iris dilator muscle, activated by the sympathetic nervous system, contracts to pull the iris outward, causing the pupil to widen. Conversely, the iris sphincter muscle, controlled by the parasympathetic nervous system, contracts to narrow the pupil. The balance between these two systems constantly adjusts pupil size in response to various stimuli, including light and internal states.
The Emotional Link to Pupil Dilation
When a person looks at someone they are attracted to or love, their pupils often dilate due to the activation of the sympathetic nervous system. This system prepares the body for action, engaging during states of arousal, interest, and pleasure.
Specific chemical messengers, known as neurotransmitters, play a significant role in this emotional response. Dopamine, often called the “happy hormone,” is released when the brain anticipates something rewarding or pleasurable, such as interacting with a loved one. This surge in dopamine can directly or indirectly influence pupil dilation. Norepinephrine, also known as noradrenaline, is another neurotransmitter closely associated with sympathetic nervous system activity and arousal, contributing to the widening of pupils.
Oxytocin, frequently referred to as the “love hormone,” is also implicated in pupil dilation during states of attraction and social bonding. This hormone is known to enhance feelings of connection and pleasure, and its release can lead to increased pupil size. The combined effect of these neurotransmitters and the resulting sympathetic nervous system activation creates the noticeable pupil dilation observed when someone is emotionally engaged with another person.
Why Dilation Matters
Pupil dilation in the context of attraction can serve as a subtle, unspoken signal in social interactions. Historically, larger pupils were often perceived as more appealing, leading to practices like using belladonna in the Renaissance to artificially dilate pupils for perceived beauty. This suggests that dilated pupils might unconsciously signal interest, receptiveness, or even a heightened state of arousal, potentially enhancing perceived attractiveness.
However, more recent research presents a nuanced view, with some studies suggesting that constricted pupils, which make the iris appear larger and brighter, are rated as more attractive. This highlights the complexity of attractiveness cues, where brighter eyes might be perceived as more appealing. Despite varied findings on perceived attractiveness, pupil dilation remains an honest signal of internal states, difficult to consciously control.
Beyond signaling attraction, pupil dilation during emotional engagement might also relate to an evolutionary advantage. When activated by excitement or interest, pupils dilate to allow more light, potentially improving vision and enhancing detail perception. This physiological response could have been beneficial for assessing potential mates or social partners, fostering deeper connection and trust in social settings.