Cold is caused by viruses transmitted through sneezing or coughing. It is estimated that most babies get inflected around 10 times a year during the first one or two years after birth. When the cold is recovered, children will acquire immunity to that strain of virus. When children reach 3 or 4 years old, they have built up sufficient immunity against certain kinds of viruses. Frequency of catching cold is reduced to 6 times a year.