Critical windows of children’s development and susceptibility to environmental toxins

Environmental factors are significant contributors to population health across the life course. Early life exposures can lead to diseases later in life. Children can be exposed to environmental factors across several critical windows of development spanning conception through adolescence. These periods are defined by behavioral and physiological characteristics associated with growth and development. Environmental chemicals are ubiquitous in our environment and can be found in air, food, drinking water, and consumer products. Environmental researchers aim to identify critical windows within these various lifestages when children are most vulnerable to the toxic effects of environmental exposures. The critical windows for some environmental chemicals are well known. For instance, exposure to alcohol or tobacco smoke during early pregnancy has been associated with increased risk of congenital anomalies and low birth weight among exposed infants. However, for many environmental exposures, little is known regarding the critical windows of exposure that result in adverse health outcomes. Children can be exposed to a wide range of factors through various routes and windows of susceptibility and exposure may also differ through the lifespan. Young children are more susceptible to environmental chemicals because, compared to adults, they breathe more air and consume more food in proportion to their body size in order to meet the requirements of growth and development. Typical hand-to-mouth behavior among infants and young children also increases their risk of exposures to environmental chemicals. This article summarizes the general state of knowledge on critical windows of exposure to environmental exposures 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.