This kind of poisoning occurs because the exposure is repeated day after day over many years. The exposure levels may be too small to cause any acute toxicity. Inhalation and skin absorption of some organic solvents at concentrations which do not cause acute toxicity may, over long periods of time, cause damage to nerve tissue. Repeated exposure to dusts containing quartz can cause scar tissue in the lungs. This leads to severe and permanent lung damage.
Most chemicals can cause both acute and chronic toxicity depending on the conditions of exposure.
The adverse health effects caused by the chemical in the two types of toxicity are often quite different. It is not usually possible to predict what the chronic toxicity of a chemical might be by looking at its acute toxicity, or vice versa. In most cases, much more is known about the acute toxicity of a chemical than its' chronic toxicity. The understanding of acute toxicity usually comes from studies with animals exposed to relatively high doses of the substances. Accidental overexposure, spills and emergencies have added to our knowledge of acute toxicity in humans.