Critical Windows of Children's Development and Susceptibility to Environmental Toxins

The concept of critical windows or periods of development and susceptibility is used to better understand the prenatal and postnatal time periods during which a developing child may be most vulnerable to environmental exposures. Some of these critical windows are well-known (e.g., alcohol or tobacco smoke during early pregnancy associated with birth defects or low birth weight), whereas others are suspected (e.g., lead or polybrominated biphenyls exposure in adolescence and altered timing of puberty), and still others have little or no data on critical timing for exposure (e.g., prenatal or postnatal exposures to drinking water contaminants and impaired immune function). This article summarizes the general state of knowledge on critical windows of exposure to environmental chemicals and resulting adverse health outcomes. Information about pregnancy outcomes and general growth and development is reviewed along with the state of knowledge for several organ systems and disease states including the nervous system, lung function and asthma, reproductive system, endocrine system, immune system, and cancer.