Toxins and carcinogens are carried into the body by air, water, soil, or food in three primary ways. They can be inhaled, ingested, or absorbed through the skin.

Inhalation involves the simple process of breathing air in through the nose or mouth. When we breathe, we are not just taking in clean air but also all of the particles dispersed in air. Oxygen and particulate matter enter the lungs and traverse the airways, ending up in small air-filled sacs called alveoli that are located deep in the lung tissue. Larger particles are filtered by the body’s natural defenses along the airways, including nose hair, cilia (hair-like projections that line the airways), and mucus. Smaller particles are carried deeper into the lungs, where they can cause irritation and disease over time. The very smallest particles actually can enter the bloodstream, where they are carried throughout the body.

Ingestion includes both eating and drinking. Toxic or carcinogenic substances can enter the body in the food or liquid that an individual eats or drinks. Along with nutrients from digested food, these substances then are absorbed through the gastrointestinal tract – stomach, small intestine, and large intestine -- into the blood stream for distribution throughout the body.

The third route of entry for toxic substances is absorption. The skin is one of the body’s major defense mechanisms against toxins and infectious organisms, but even it is not perfect. Toxic substances can cause irritation at the site of contact or can be absorbed through the skin into the bloodstream, where they can circulate to other parts of the body

Progression from environmental exposure to illness

There are five basic steps progressing from exposure to a toxic substance through development of detectable disease.

Exposure. An individual is exposed to a chemical, biologic, or physical agent that is potentially toxic or carcinogenic. The individual may or may not have knowledge of the presence of the substance.

Entry. The substance enters the body carried by air, water, food, or soil.

Accumulation. Over time, enough of the toxin or carcinogen enters the body and accumulates until the quantity is high enough to cause some type of health effect.

Early changes. The toxin or carcinogen alters some part of the body, often on a microscopic level. A group of cells affected by the toxin now may look or act differently. The person exposed may not have symptoms of disease or any detectable abnormality on routine medical testing at this time.

Detectable disease. The person who has been exposed to the toxin now has developed an actual disease that is detectable by symptoms and/or medical testing.

Moving from one stage to the next depends on a number of factors, including a person’s genetic or inherited tendency to develop a disease, diet, physical activity, personal habits such as smoking, use of certain medications, and exposure to other environmental toxins at the same time. Disease can occur immediately, several hours, or many years after exposure. For instance, an individual may develop cancer several decades after an environmental exposure.