Up until now, most people have accepted kissing with their eyes closed as "just one of those things that happen".
Well, psychologists have now revealed the real reason why we close our eyes when locking lips.
Turns out, the brain can't deal with more than two things at once - and needs to focus on the task at hand. To adapt, we simply close our eyes when we kiss.
The study on vision and tactile sensory experience was carried out by Royal Holloway University of London, and concluded that our brain struggles to process another sense while also concentrating on the visual stimuli.
Cognitive psychologists Polly Dalton and Sandra Murphy found "tactile [sense of touch] awareness depends on the level of perceptual load in a concurrent visual task".
The study, which has been published in the Journal of Experimental Psychology: Human Perception and Performance, was actually reached without studying any couples locking lips.
Instead, the participants were given visual tasks to complete while their tactile sense was measured.
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The visual part of the study saw participants completing letter-searching tasks of varying difficulty, while the tactile response was measured by their response to small vibrations applied to their hands.
The analysis showed that people were less responsive to the tactile sense as their eyes did more work.
The same explanation applies to other pleasurable activities on the tactile sense, like dancing and sex, where people wish to focus on touch rather that other potentially distracting sensory experiences.
"These results could explain why we close our eyes when we want to focus attention on another sense," Ms Dalton told The Independent.
"Shutting out the visual input leaves more mental resources to focus on other aspects of our experience."