This age-old tradition of keeping half cut onions or onion slices in socks overnight originated in the early 1500s, when the world was struggling with Bubonic Plague, a deadly pandemic. In fact, it was believed that red onions had the power to heal infections and several ailments including cold, fever and prevent Bubonic Plague. According to the National Onion Association, it was believed that infections were spread by Miasma or poisonous air. The strong pungent smell of onions was believed to prevent the infection caused due to the poisonous air.