There have been many attempts to categorize toxic effects and to define them in various ways. Generally, the terms “acute” and “chronic” are used to delineate between effects on the basis of severity or duration.

The first method or acute exposure is the exposure to a hazardous substance over a short period of time or at a high dose. A reaction to a chemical can occur at the time of exposure, and might include vomiting, eye irritation, or other symptoms that often may be readily linked to a chemical exposure. These are immediate and adverse effects.

The second method or chronic exposure is the exposure to a hazardous substance over a long period of time. If a carpenter used a stripper regularly and breathed in a little of it 8 hours a day for 40 years, a chronic exposure would result. This type of exposure occurs when a person is repeatedly exposed to the same chemical or hazardous substance over a long period of time at very low levels.

Similarly, the term chronic effect is often used to cover only carcinogenicity, teratogenicity, and mutagenicity (terms to be discussed below). These effects are obviously a concern in the workplace, but again do not adequately cover the area of chronic effects, excluding, for example, blood dyscrasias (such as anemia), chronic bronchitis, and liver atrophy (wasting, losing function, or size).