How do scientists decide which exposures are high risk and which are low risk? Risk assessment involves three factors:

1. Potency: The potential of a given amount of a substance to cause cancer. Benzene, for example, is quite potent because even small amounts of it can increase cancer risk. Other compounds, such as chloroform, are less potent; they require higher exposures to increase the risk by the same degree.

2. Type of exposure: Whether the exposure is one-time (acute) or long-term (chronic), and whether it is unavoidable (in the workplace, for example, or in the air we breathe).

3. Dose response: A dose-response trend describes what happens to cancer risk as the level of exposure increases or decreases.