Exposure to biocontaminants is associated with behavioural problems and poorer cognitive function. Our study assesses the associations between early life exposure to home dampness, pets and farm animal contact and cognitive function and social competences in 4-year old children, and the associations between these indoor factors and microbial compounds (bacterial endotoxin and fungal extracellular polysaccharides). A Spanish population-based birth-cohort enrolled 482 children, and 424 of them underwent psychometric testing at 4 years of age, including the McCarthy Scales of Child Abilities (MSCA) and the California Preschool Social Competence Scale (CPSCS). Information on pet ownership, farm animal contact and home dampness was periodically reported by the parents through questionnaires. Microbial compounds were measured in living room sofa dust collected at the age of 3 months. Persistent home dampness during early life significantly decreased the general score of MSCA by 4.9 points (95% CI: -8.9; -0.8), and it decreased the CPSCS by 6.5 points (95% CI: -12.2; -0.9) in the child's bedroom. Cat or dog ownership were not associated with the outcomes, but occasional farm animal contact increased the general cognitive score of MSCA by 5.6 points (95% CI: 1.8; 9.3). Cat and dog ownership were associated with higher levels of endotoxins in home dust. None of the measured microbial compounds were related with the psychometric tests scores. In conclusion, damp housing in early life may have adverse effects on neuropsychological development at 4 years old. More research is needed to explore the possible involvement of mycotoxins in the observed results.
