Given the connection to asthma you mentioned, here is something that you might also find interesting per this analysis of a few different factors: https://www.

Given the connection to asthma you mentioned, here is something that you might also find interesting per this analysis of a few different factors: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877483/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877483/ > Results of this meta-analysis indicated an inverse association between atopy/allergies and childhood ALL; the pooled odds of any reported atopy/allergy were 31% lower among cases than among controls and were 21% lower for asthma, 26% lower for eczema, and 45% lower for hay fever. I've always considered myself unlucky for having hay fever and eczema since childhood, but what if those conditions (whether they be from overly clean environments or the opposite) actually do play a role in preventing childhood leukemia? It makes sense that a child with open sores from dermatitis, or with a persistently runny nose and frequent sneezing, would be better at collecting germs than one without those things. I'm not familiar enough with asthma to know if that could actually help collect germs, or if it's just that eczema and hay fever are so commonly associated with asthma that it's just a common comorbid condition (the "allergic march" as it's called).