Many different viruses can cause a cold.
Over a hundred have been identified so far. A virus is a disease-producing agent so small that it goes right through the very fine filter that stops bacteria. These cold-causing viruses are present in great numbers in your nose and throat when you have a cold. They are carried on the droplets you expel when talking, coughing, or sneezing. Though a virus causes your cold, a number of conditions seem to increase your susceptibility.