Changes in human activity which decrease our exposure to microbes:
Increased hand washing: Many hand soaps today are anti-bacterial and remove microbes from our hands and thus our overall exposure
Urbanization of towns: The movement away from farm-lifestyles and into cities decreased our exposure to farm animals and the microbes they carry.
Modern toilets and sewage: Fecal matter contains many microbes and our toilets and sewage have improved, reducing the risk of exposure to it and thus microbes.
Cleaning supplies: Household cleaning supplies are now used to kill bacteria on many different surfaces.
More time indoors: the outdoors, especially the dirt, is filled with many, many microbes.
Mode of Delivery for birth: Cesarean sections do not introduce newborns to the bacteria in the vaginal canal like in more traditional vaginal deliveries.
Antibiotic use: The point of these are to kill bacteria and other life without being specific to the kind, and reducing the total number that live in us.
Limited exposure to others: Growing up with siblings or hanging out with other children increase our exposure to others, and thus having a limited exposure to others does the opposite.
