We close our eyes when we kiss primarily to enhance the sensory experience and allow our brains to focus on the act itself.
Enhancing Sensory Perception
Closing our eyes during a kiss allows us to heighten our other senses. With one sense (sight) temporarily suppressed, our brain can dedicate more processing power to other senses like touch, taste, and smell, making the experience more intense and intimate. As noted in a Reddit discussion (r/explainlikeimfive), "When kissing, your eyes don't have much function, so closing them allows you to enhance your other senses that are more...". This heightened sensory input contributes to a more fulfilling and emotionally charged experience.
Focusing the Brain
Psychologists suggest that closing our eyes during a kiss helps the brain concentrate on the act of kissing itself. This is supported by the statement from the Independent article (https://www.independent.co.uk/news/science/why-we-kiss-with-eyes-closed-psychologists-research-a6943731.html): "People close their eyes while kissing to allow the brain to properly focus on the task in hand, psychologists have said." By minimizing visual distractions, the brain can more effectively process the physical sensations and emotional connection involved in a kiss.
Emotional Intensity
Many sources suggest that closing one's eyes during intimate moments, such as kissing, enhances the emotional experience. As one Quora post notes (https://www.quora.com/Why-do-we-close-our-eyes-when-praying-dreaming-kissing-or-crying-Even-during-lovemaking-we-turn-off-the-light), when experiencing potent emotions, closing our eyes allows us to fully immerse ourselves in the feeling, unburdened by visual stimuli. This aligns with the idea that closing eyes during a kiss can increase emotional vulnerability and intensify the feelings of intimacy and connection.
