We face risks every day, every time we get in a car, on a bike, or on a plane. Sometimes we knowingly increase our risk, by not wearing a seat belt or by smoking. Studies show, though, that public perceptions of risks rarely reflect the actually likelihood of the potential harm.
Risk assessment is a field of scientific research dedicated to defining and measuring risk.
Risk experts calculate the likelihood of an event resulting in a specific consequence. For environmental health risks, researchers combine information about the toxicity of a a substance with the amount of exposure a population has to the substance to calculate what is likely to happen. This relationship, the dose-response relationship, between toxicity and exposure is key to risk assessment. Uncertainty arises, however, from the question of how much exposure is necessary to create a health risk. Substances like mercury and benzene are known to be toxic in small amounts, but there is less certainty about the threshold of exposure at which other substances are dangerous to human health.