This usually happens if you touch a surface that has germs on it -- a computer keyboard, doorknob, or spoon, for example -- and then touch your nose or mouth. You can also catch it if you're near someone who is sick and sneezes into the air. A cold begins when a virus attaches to the lining of your nose or throat. Your immune system -- the body's defense against germs -- sends out white blood cells to attack this invader.