Human behaviors that could decrease exposure to microbes:
Antibiotic use. Antibiotics decrease microbial populations of bad microbes as well as microbes that are important for our microbiota. Taking antibiotics will undoubtably decrease a person’s exposure to microbes by getting rid of both good and bad bacteria.
Over sterilization of environment. By cleaning everything all of the time, a lot of microbial populations can be decreased in a persons environment and never make it on or into their bodies. For example, over cleaning of children’s toys that often end up in their mouths could potentially have a negative affect on their microbiota / immunity.
Limited interaction with other people/children. Since people are covered with microbes, it’s no surprise that interactions with other humans can diversify our own microbial populations. If a person is kept away from other people, they won’t come in contact with other people’s microbes.
Not being allowed to play in dirt. Soil is full of bacteria. If a child is restricted from playing in the dirt, that child won’t be exposed to certain microbes at all.
Homeschool opposed to public or private school. This scenario is similar to the limited interactions with other people example. Staying in one particular environment like a persons home versus going to a public school or public area will decrease ones exposure to microbes.
Taking too many baths. This is over sterilization of your body. There are many microbes on the outside of the human body. By washing them off, a person is decreasing potentially beneficial microbes.