> Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world.[23] This is true for asthma and other chronic inflammatory disorders.[18] The increase in allergy rates is primarily attributed to diet and reduced microbiome diversity, although the mechanistic reasons are unclear.
That certainly seems reasonable -- that the immune system needs practice or otherwise it will start using its ammo on other "hey that's me!" stuff and cause auto-immune diseases.
But I also have to wonder if the kids with auto-immune diseases or "common" allergies elsewhere might just die the first time they encounter some event that'd otherwise be caught and treated in "the first world" ?
From the same wikipedia page:
> The hygiene hypothesis has difficulty explaining why allergic diseases also occur in less affluent regions. Additionally, exposure to some microbial species actually increases future susceptibility to disease instead, as in the case of infection with rhinovirus (the main source of the common cold) which increases the risk of asthma
I think having a common cold infection each year does not bring any benefits, it certainly does not make anybody immune to common cold
I remember having a lot of colds as a kid but haven't had one for years now. I may have gained immunity to a good number of the 200+ different types.