P ediatric environmental health is the diagnosis, treatment, and prevention of illness caused by preconception, prenatal, perinatal, and pediatric exposures to environmental hazards; and the creation of healthy environments for children. Exposure to pollutants in air, food, and water as well as chemicals in the environment can be potentially helpful or harmful. The toxicity of the vast majority of the 85,000 chemicals manufactured in the United States is unknown. This coupled with increases in the prevalence of asthma, attention deficit disorder, birth defects, cancer, and developmental delay have lead many to question whether there is a causal relation. Response to environmental toxins varies according to a person’s physical, biological, and behavioral characteristics. Biological or physiologic characteristics determine how the body absorbs, distributes, and metabolizes environmental exposures and behavior varies according to a person’s developmental stage and social milieu. Additionally, specific responses to acute and chronic exposures differ from person to person. Physical exposures vary with age and development. Because they are growing, children drink more water, eat more food, and breathe more air per body size and surface area than adults. Because of their higher metabolic rate, children consume more oxygen than adults and may have more adverse effects to air pollutants. Infants in the first 6 months of life drink 7 times as much water per pound as does the average adult. Children ages 1 to 5 years of age eat 3 to 4 times more food per pound than the average adult. In addition, children have unique food preferences. For example, the average 1-year-old drinks 21 times more apple juice and 11 times more grape juice and eats more grapes, bananas, pears, carrots, and broccoli than does the average adult. Biologically, a child’s immature metabolic pathways less readily detoxify and excrete certain toxins. Additionally, nonambulatory children are not able to remove themselves from potentially harmful locations. Behaviorally, children live and play closer to the ground, which increases their exposure. Their handto-mouth behavior increases their risk as well. With more years of life before them, early environmental exposures may permit the development of chronic diseases.