There is a broad theory called the hygiene hypothesis, which states (I am paraphrasing here) that the increase in occurrences of allergies and other autoimmune illnesses over time is a result of decreased germ exposure in childhood, and that exposure to more microbes and germs as a child can help their immune system properly identify and not overreact to perceived pathogens.13 While we don’t have conclusive proof that this is true, there is some evidence backing the theory in the form of laboratory studies of particular cells and comparisons across cultures in rates of various diseases.
