Stepping out from a dim interior into the bright sunlight causes an involuntary reaction, causing faces to scrunch and eyes to squint. It is now believed that this type of facial contortion can negatively impact mood, according to a study published in the journal Cognition and Emotion.
Tests were performed that measured whether levels of aggression can be influenced by the squint-and-frown reflex people have when they face the sun. The hypothesis in question is based on the idea that a sun-induced grimace involves the same set of facial muscles as the expression of anger.
Randomly selected participants walking along a beach, both with and without sunglasses, were asked to answer a brief survey. “We found that participants walking against the sun without sunglasses scored higher in a self-report measure of anger and aggression compared to those walking with the sun behind and/or wearing sunglasses” the authors report.
They also suggested that frowning at the sun affects mood very quickly, as they did not find any effect of walking time on self-reported aggressiveness.
It has long been thought that Botox injections may help improve mood, simply because those who receive them are no longer able to frown. The evidence gathered in this experiment seem to support this.