PLAYING IN THE DIRT AND GRASS IS GOOD FOR YOUR IMMUNE SYSTEM!
This is a collection of research on the benefits of green spaces to our bodies - young and old. Some highlights:
We need to consider measures that not only preserve the natural environment but also reconnect us with nature. We need to preserve our connection to the soil and green spaces, we need to expose our children to natural environments.
Exposure to a diversity of soil and plant microbes is critical to healthy immune system development in part because evolutionarily we evolved to deal with these "old neighbors". Otherwise the immune system essentially becomes dysfunctional leading to autoimmune responses and allergies.
Infectious diseases are of relatively modern origin associated with living in densely populated communites. THESE we have not evolved yet a "friendly" relationship with and so still need to avoid as much as possible (eg handwashing around contact with people and the things they use).
"Urbanization can't be stopped, but perhaps we should take the planning of green spaces in cities more seriously."
SO - clean homes are still a good idea especially if filled with synthetic materials but keep a lot of plants around AND GET DIRTY in the natural world. Take any opportunity you get to develop appropriate immune responses by exposure to microbes in the natural world, especially soil and plants.
Properly Landscaped Turfgrass Fields Reduce Pollution
Source: Digital Guide to Grass Field Maintenance: Benefits of Natural Grass Sports Surfaces (Sports Turf Managers Association)