Want to prevent your children from having allergies or asthma? A recent study adds support to increasing evidence that growing up on a farm, or living among multiple pets in the first year of life is protective against developing allergies and asthma. This is because exposure to lots of animal and outdoor soil bacteria in early childhood is good for the developing immune system. The study, which was conducted by Finland's National Institute of Health and Welfare, carried this line of work further and found that this type of beneficial farm microbial exposure could be duplicated in non-farm homes.
They found that children's risk of developing asthma decreased as the similarity of their home's bacteria became more similar to that of farm homes. The researchers analyzed living room dust from homes and found that certain types of outdoor soil microbes were beneficial for preventing asthma. They found higher levels of these bacteria (and archaea, another microbe) in homes where people wore their outdoor shoes in the house, as well as 3 or more children, and increased moisture in houses. The types of fungi found in the dust of farm and non-farm houses didn't seem to matter. The researchers mention that the same kind of protective (for asthma) results of soil microbes has also been shown in mice.
Additional thoughts reading this: The study results can be interpreted as playing and crawling outdoors is definitely beneficial to children's health, especially young children. Exposure to soil microbes! And, of course, having pets. But wearing outdoor shoes indoors is problematic in areas with high lawn and garden pesticide use (e.g. suburban NY and NJ!) because studies show the pesticides get tracked indoors. This same problem occurs in areas with high lead levels (around older homes) or other heavy metals.