This is unlikely to be true for respiratory viruses. Compared to an ancestral environment, we have: * Much less contact with bacteria, dirt, allergens, due to

This is unlikely to be true for respiratory viruses. Compared to an ancestral environment, we have: * Much less contact with bacteria, dirt, allergens, due to sterilization * Much more contact with respiratory viruses, due to enclosed spaces and modern energy efficiency standards The whole overactive immune system/hygiene hypothesis is much more likely linked to lack of exposure to the first group of pathogens and substances.