Asthma, rhinitis and eczema (allergic or non-allergic) have increased throughout the world during the last decades, especially among children. Changes in the indoor environment are suspected to be important causes. China has experienced a dramatic change in indoor environmental exposures during the past two decades. However, such changes and their associations with children’s asthma and other health aspects have not been thoroughly studied. China, Children, Homes, Health (CCHH), Phase I, was a cross-sectional questionnaire survey of 48219 children 1–8 years old in 10 Chinese cities during 2010–2012. The questionnaire includes the International Study of Asthma and Allergies in Childhood (ISAAC) core health questions and additional questions regarding housing, life habits and outdoor environment. In health analyses, children aged 3–6 years old were included. The prevalences of doctor diagnosed asthma varied from 1.7% to 9.8% (mean 6.8%), a large increase from 0.91% in 1999 and 1.50% in 2000. The prevalence of wheeze, rhinitis and atopic eczema (last 12 months) varied from 13.9% to 23.7%, 24.0% to 50.8% and 4.8% to 15.8%, respectively. Taiyuan had the lowest prevalences of all illnesses and Shanghai the highest, except for wheezewhere the highest value was for Urumqi. We found (1) no obvious association between disease prevalences and ambient PM₁₀ concentrations and (2) higher prevalences of disease in humid climates with hot summers and cold winters, but with no centrally heated buildings. Associations between the diseases and economic status as indexed by Gross Domestic Product (GDP) requires further study.

Recent studies show that formaldehyde participates in DNA demethylation/methylation cycle. Emerging evidence identifies that neuronal activity induces global DNA demethylation and re-methylation; and DNA methylation is a critical step for memory formation. These data suggest that endogenous formaldehyde may intrinsically link learning-responsive DNA methylation status and memory formation. Here, we report that during spatial memory formation process, spatial training induces an initial global DNA demethylation and subsequent re-methylation associated with hippocampal formaldehyde elevation then decline to baseline level in Sprague Dawley rats. Scavenging this elevated formaldehyde by formaldehyde-degrading enzyme (FDH), or enhancing DNA demethylation by a DNA demethylating agent, both led to spatial memory deficits by blocking DNA re-methylation in rats. Furthermore, we found that the normal adult rats intrahippocampally injected with excess formaldehyde can imitate the aged-related spatial memory deficits and global DNA methylation decline. These findings indicate that aging-associated excess formaldheyde contributes to cognitive decline during aging.