It is estimated that Americans spend approximately 92% of their time indoors, yet we know little of the diversity of microbes (bacterial and fungal) that exist in the household environment and how they influence gut microbiome composition and the health of residents. This is particularly true during infancy, a period in which the gut microbiome is assembling in parallel with immune maturation. The NIH/NIAID recently supported a study led by Dr. Christine Johnson that in part, examines the bacterial communities present in household dust and stool samples (n= 340) collected in parallel from homes and their resident infants (6 months old) as part of a birth cohort based in the Detroit area. The Sloan-funded study will examine the fungal communities present in these same samples and examine the relationship between fungal community composition of house dust and it’s influence on the fungal content of the infant gastrointestinal microbiota. In addition, the household characteristics that most strongly influence the composition of fungal communities in the household will be determined. Finally, using clinically defined allergic disease outcomes, the study aims to determine whether increased early-life exposure to particular fungal species in the household environment are associated with aberrant patterns of infant gut microbiome composition and development of allergic disease in childhood.