This supports old Dr. Page's advice to my mother to let me play "in the dirt" in 1941. No allergies yet. For what ever testimonial support is worth.
Exposure to Certain Allergens, Bacteria Before Age 1 Might Reduce Allergy Risk — Physician’s First Watch
Exposure to Certain Allergens, Bacteria Before Age 1 Might Reduce Allergy Risk
By Amy Orciari Herman
Infants exposed to high levels of certain allergens and bacteria before age 1 year have a lower risk for wheeze and atopy at age 3, according to a Journal of Allergy and Clinical Immunology study.
U.S. researchers studied some 500 infants at high risk for asthma in four inner-city areas. Household dust samples were collected annually and tested for allergenic proteins. For 100 infants, the bacterial content of house dust collected at age 3 months was also analyzed.
Overall allergen exposure through age 3 years was associated with allergic sensitization, and, in turn, recurrent wheeze. However, children with high levels of exposure to cockroach, mouse, and cat allergens before age 1 were less likely to have recurrent wheeze at age 3. In addition, first-year exposure to certain bacteria (from phyla Bacteroidetes and Firmicutes) appeared protective against atopy and wheeze.
The authors call the first few months of life "critical" in allergic disease development, noting that "concomitant exposure to high levels of certain allergens and bacteria ... might be beneficial."