Why it works
Pupils dilate not only in the dark, but also with interest, arousal and mental effort. It's an involuntary reaction that can't be faked in the usual way, so it's read as an honest signal.
The other person picks up on it unconsciously. In experiments, people were shown two identical portraits that differed only in pupil size and asked to choose the more attractive one. They chose the version with dilated pupils but couldn't explain why.
Effect of pupil size on attractiveness ratings: supported, but moderate
The effect is moderate because the result depends on the conditions. It's more noticeable when looking at a face of the opposite sex and from a short distance, while in other setups it may almost disappear.
There's also an opposite effect: the pupils of people talking to each other adjust slightly to one another. Looking at dilated pupils causes a person to dilate their own pupils involuntarily, and this is linked to a feeling of closeness during conversation.
What it cost
It was a harmless cosmetic.
The plant contains substances that paralyze the muscle that constricts the pupil. The eye stops focusing properly, nothing nearby can be seen, and bright light becomes intolerable. With constant use, vision deteriorates irreversibly.
In other words, beauty was literally bought at the price of sight: a woman looked interested while barely seeing the person she was looking at. The plant's name in Italian means "beautiful woman."
The same logic appears in many historical beauty remedies: lead white for paleness, mercury for breakouts and arsenic for complexion. They all have one thing in common: a quick visible result and delayed harm.
The substance from this plant is still used today, but only as prescribed by a doctor: it is used deliberately to dilate the pupil when examining the back of the eye, and its effects wear off within a few hours.
Why did people put poisonous plant juice in their eyes?
What did it cost them?
Sources
- Belladonna extract was used to dilate the pupils for cosmetic purposes
- substances in the plant paralyze the muscle that constricts the pupil, causing impaired accommodation and photophobia. The effect of pupil size on attractiveness ratings was demonstrated in experiments in the 1960s
Next in the “Attraction” series
3 articles in full on the site, 4 more in the app
