A case of cold feet can do more than spoil a good opportunity, it can even make you sick. “When feet get chilly, it actually tightens up the blood vessels in the sinuses,” says Ron Eccles, Ph.D., director of the Common Cold Centre at Britain’s Cardiff University. Here's how: Chilly feet send a message to your brain to take action to conserve your body's heat. The brain responds by firing out messages that reduce blood flow to areas where heat is lost quickly, and that includes the mucus membranes of the sinuses. When blood flow is reduced to the sinuses, so is the flow of infection-fighting white blood cells, leaving your body more vulnerable when viruses invade. Fortunately, a recent study reveals that keeping your feet warm, with a pair of plush socks, for instance, can cut risk of colds as much as 67 percent.