On the sunniest days, we squint, and squinting makes us angry, explains Daniele Marzoli, PhD, a psychologist at Italy's University of Chieti-Pescara who tracked people's emotions when the sun was either in their face or to their back. (The upshot: Squinters reported feeling 44 percent more agitated and aggressive
.) Problem is, your screwed-up expression—forehead furrowed, eyes narrowed, mouth twisted—is essentially a frown. And because mood and facial muscles are linked, your face signals to your brain that you're irritated (even if weren't...initially). To make matters worse, the tetchiness flares up almost instantly
, Marzoli explains. Luckily, this one has a simple, fast-acting and potentially elegant remedy: sunglasses.