There's a well established theory called the "Hygiene Hypothesis" that says exactly this - https://www.fda.gov/vaccines-blood-biologics/consumers-biologics/asth

There's a well established theory called the "Hygiene Hypothesis" that says exactly this - https://www.fda.gov/vaccines-blood-biologics/consumers-biologics/asthma-hygiene-hypothesis https://www.fda.gov/vaccines-blood-biologics/consumers-biolo...