Chemical compounds ubiquitous in our food, air, and water are now found in every person. The bioaccumulation of these compounds in some individuals can lead to a variety of metabolic and systemic dysfunctions, and in some cases outright disease states. The systems most affected by these xenobiotic compounds include the immune, neurological, and endocrine systems. Toxicity in these systems can lead to immune dysfunction, autoimmunity, asthma, allergies, cancers, cognitive deficit, mood changes, neurological illnesses, changes in libido, reproductive dysfunction, and glucose dysregulation. Chemicals and their effects on these systems are reviewed in this article. Subsequent articles in this series will focus on therapeutic regimens to combat the toxic effects of these and other compounds.