When a substance is absorbed into the body, its chemical structure may be changed or metabolized to a substance that is more toxic or less toxic. For example, carbon tetrachloride, once a commonly used solvent, is changed by the body into a more toxic chemical that causes liver damage. For some other chemicals, metabolism changes the chemical into a form that is more easily eliminated by the body. A chemical can cause health effects only when it contacts or enters the body. Exposure to a substance can occur by inhalation, ingestion or direct contact.
Chemicals can enter and irritate the nose, air passages and lungs.
They can become deposited in the airways or be absorbed by the lungs into the bloodstream. The blood can then carry these substances to the rest of the body. Chemicals that get in or on food, cigarettes, utensils or hands can be swallowed. Children are at greater risk of ingesting substances found in dust or soil because they often put their fingers or other objects in their mouths. Lead in paint chips is a good example.