Maybe have you hitherto suffered through a common cold virus? By chance did you heal from it? Certainly you got over it! You cannot heal a common cold directly, but your body usually develops immunity to a certain cold infection within a few weeks. That is called healed by your personal immune response!

Adults have actually in the past had a lot of the rhinitis viruses. Parents have developed immunity to the colds they have suffered from. Therefore there are not quite as many runny nose viruses around for grownups to catch. That is why grownups just get infected with a couple of colds annually whereas children acquire 10-12 runny noses per year.
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