That's probably because pathogens compete with the natural microbiome, and in some cases, they win in small ways, even if the host/infected isnt killed by the infection, some of the good microbes may have died off in the battle, never to return.
Allergy study on 'wild' mice challenges the hygiene hypothesis
September 29, 2023
Source: Karolinska Institute
Summary: The notion that some level of microbial exposure might reduce our risk of developing allergies has arisen over the last few decades and has been termed the hygiene hypothesis. Now, an article challenges this hypothesis by showing that mice with high infectious exposures from birth have the same, if not an even greater ability to develop allergic immune responses than 'clean' laboratory mice.
Allergy study on 'wild' mice challenges the hygiene hypothesis
September 29, 2023
Source: Karolinska Institute
Summary: The notion that some level of microbial exposure might reduce our risk of developing allergies has arisen over the last few decades and has been termed the hygiene hypothesis. Now, an article challenges this hypothesis by showing that mice with high infectious exposures from birth have the same, if not an even greater ability to develop allergic immune responses than 'clean' laboratory mice.

Allergy study on 'wild' mice challenges the hygiene hypothesis
The notion that some level of microbial exposure might reduce our risk of developing allergies has arisen over the last few decades and has been termed the hygiene hypothesis. Now, an article challenges this hypothesis by showing that mice with high infectious exposures from birth have the same...
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