Although more than 200 viruses can cause a common cold, the rhinovirus is the most common culprit, and it's highly contagious.

A cold virus enters your body through your mouth or nose, but it's likely you also had a "hand" in your own illness. The virus can spread through droplets in the air when someone who is sick coughs, sneezes or talks. But it also spreads by hand-to-hand contact with someone who has a cold or by using shared objects, such as utensils, towels, toys or telephones. Touch your eyes, nose or mouth after such contact or exposure, and you're likely to "catch" a cold.