Conclusion
The present systematic review and meta-analysis provides evidence that
exposure to higher environmental biodiversity has a protective effect on
the development of asthma, allergic sensitization, and wheezing.
Although the evidence on the effect of inner layer (human microbiota)
biodiversity suggested that bacterial diversity was slightly higher
among individuals with asthma, there was no consistent evidence of an
association between inner layer biodiversity and asthma, wheezing or
allergic sensitization.