-Although cleaner water normally sounds like a good thing, the ingestion of water from rivers and wells that indigenous people consumed had many more microbes from the environment. The water consumes now is so highly processed and removed of microbes we have much less exposure.
-With couples choosing to produce less offspring for financial purposes, there are fewer microbes that can be exposed to people at younger ages. As siblings may live in the same environment, they are not glued to each other and tend to make different friends, hang out in different places, and do different activities. This increases the exposure of various microbes to individuals from their siblings who experience different environments. The exchange of microbes between siblings is a factor.
Born via Cesarian section:
-Being delivered by c-section changes what microbes an individual is immediately exposed to at birth. It has been shown that vaginal bacteria are very beneficial to infant development. People who are born via c-section do not get exposed to this beneficial bacteria and are instead immediately exposed to skin bacteria. By missing out on being colonized by vaginal bacteria, those individuals miss out on the health benefits that come with them.
Taking many antibiotics as a child or infant changes the stable structure of microbial communities. They can kill healthy bacteria that are used in immune defense or metabolism and have co-existed with humans for thousands of years, such as H.pylori. The use of antibiotics selectively permits certain microbes to inhabit while others cannot, which can last for years after ceasing the use of the antibiotic.
Decline in breastfeeding:
-The decline in breastfeeding and increase in formula feeding has decreased microbe exposure. The oral microbiome of infants will have greater colonization of microbes from the breast and from the milk that is beneficial, while formula infants will not. Additionally, the gut microbiome is further matured in infants who drink breast milk and need to breakdown the sugars/fats that are present in breast milk.
Playing outside as a child:
-Children who play outside are exposed to many more microbes than those who stay inside. Acts such as eating dirt as a child can expose an individual to many microbes as there is a lot in soil. Additionally, playing with other children outside can increase the likelihood of exchanging microbes and being exposed to germs from the other child’s environment.