A cold is caused by a virus. And it's not just one type of virus. More than 200 viruses cause colds. A cold virus attacks healthy cells of the nose, throat, or lungs. The virus gets into the cells and takes control. A single virus makes hundreds or thousands of cold viruses inside each cell. Eventually, the cell bursts open and dies. The viruses, though, escape and attack other healthy cells. By now you're sneezing and coughing. Your throat is sore. The viruses keep infecting your healthy cells.