The concept of the precautionary principle has been around a long time in sayings such as "an ounce of prevention is worth a pound of cure" or "better safe than sorry or "look before you leap". The term precautionary principle as it is now being used in environmental and public health means that when an activity poses risk to human health or the environment, precautionary measures should be taken, even if cause-and-effect relationships are not fully established scientifically. In environmental health, this means that when an activity poses risk to human health or the environment, precautionary measures should be taken, even if cause-and-effect relationships are not fully established scientifically. It is often a challenge to scientists and government agencies to apply the precautionary principle.

The precautionary principle demands proof of safety of an activity or substance. Neither the federal nor state governments have established specific criteria or passed specific environmental regulation to implement this principle. Currently, a new industrial chemical can enter the marketplace with almost no safety testing. For a chemical to be removed from the marketplace, there must be scientific evidence that it is unsafe and harms human health. Health studies of workers and/or communities exposed to chemicals can provide information showing that a chemical may cause disease. Application of the precautionary principle would end exposure to workers and communities that might affect their health.

The precautionary principle has become part of chemical policy in the European Union and Canada. The European Union is beginning to implement the policy into regulation under the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) program. Beginning July 2008, REACH requires the registration of new and old chemicals. REACH will apply to 30,000 chemicals that are produced, imported or used in quantities greater than one ton. However, most of the emphasis on testing will be for chemicals produced, imported or used in quantities greater than 10 tons. REACH requires basic human and environmental toxicity data for both new and existing chemicals. This testing and safety of the chemical is the responsibility of the industry, not the government. Although there is an industry effort to limit the amount of data publicly available, REACH calls for making testing and other toxicity data publicly available. This database could be an important resource for United States citizens.