Cold can be caused by a lot of viruses and because new cold viruses constantly develop, the body never builds up resistance against all of them. Due to these reasons, colds are a frequent and recurring problem, in fact the most frequently occurring illness in the world.
Children in preschool and elementary school can have 6 to 12 bouts of cold per year while adolescents and adults, typically have two to four cold bouts per year. It occurs most frequently during winter and monsoon season.
Factors that lead to cold infections could be over-crowded areas, variation in weather conditions, smoke, dust, odours or pre-existing allergies, chronic sinusitis, septic tonsillitis or any related infection of the nasopharynx.