Skip to McMaster Navigation Skip to Site Navigation Skip to main content
McMaster logo

Precautionary Principle

Precautionary thinking hearkens back to our prehistoric propensity to evaluate risk before taking action. As a formalized principle, it first appeared in policies relating to the protection of the environment in the 1970s. Outside of environmental protection, the precautionary principle is most often applied in areas related to human health, such as public health, food, medicine/drugs, and medical research. The prevalence of the concept in these fields also means it is often relevant in the adjacent field of global health.

There is scholarly debate about the common features of the various versions of the precautionary principle. When the principle appears in guidance or regulatory documents, the principle places limitations on a practice or a technology purported to carry serious risks, even if the evidence of these risks is inconclusive. As such, the precautionary principle is highly controversial: it is often applied in domains that are very important to people (e.g., health, the environment, and food) — and its use or misuse can have profound effects on stakeholders.

When applied properly, the precautionary principle can protect people from uncertain risk. However, when misapplied it can stifle potentially life-saving innovation. Thus, clarity on the definition of the precautionary principle, as well as how it works and how it ought to be applied, is crucial for policy makers, innovators, community members, and stakeholders across an array of fields related to global health.

Expandable List

Origin and Development of the Precautionary Principle (PP)
Precautionary thinking is by no means a new phenomenon. Humans have always faced risk, and its assessment and management have been crucial for human survival and progress since prehistoric times. This remains the case today, as interconnectedness makes risk a global concern. Climate change, economic crises, the spread of viruses, and international conflict demonstrate the need for effective risk management at local, national, and international levels.1

Concurrent with the increased interconnectedness of global risk, a relatively new phenomenon has emerged since the late 1970s: the formalization and codification of precautionary thinking in public policy and the rule of law. This has taken the form of the precautionary principle (PP). The PP has been variously summarized as “better safe than sorry,” “uncertainty is no excuse for inaction,” “uncertainty requires action,” and as a restating of the Hippocratic oath, “first, do no harm.”1,2

In fact, these are oversimplifications or, in some cases, conceptual predecessors of the PP in the history of human precautionary thinking. When formalized in policy documents, the PP almost always involves a policy decision regarding some action or intervention, based on the relationship between a purported risk of that action/intervention and the degree of scientific certainty of that risk being realized.

Landmark Formulations of the PP:

  • The first time a recognizable version appeared internationally was in the 1987 Ministerial Declaration of the Second International Conference on the Protection of the North Sea, as follows:
    • “In order to protect the North Sea from possibly damaging effects of the most dangerous substances, a precautionary approach is necessary which may require action to control inputs of such substances even before a causal link has been established by absolutely clear scientific evidence.”3
  • Five years later, the PP was enshrined (in perhaps its most referenced formulation) as the guiding principle of the Rio Declaration on Environment and Development , formulated as follows:
    • “In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”4
  • By the mid-1990s, the PP was a staple of international environmental policy, more or less explicitly incorporated into all international treaties on environmental protection.

Significant Scholarly Dispute
Despite becoming a mainstay in international environmental policy and verging on status as a general principle of law in some parts of the world, the PP is hotly disputed among academics. Everything from its logical coherence to whether the term has any determinable referent has been subject to debate. Perhaps most famously, Cass Sunstein argued that the principle is either vacuous (in its weak forms) or incoherent and self-contradictory (in its strong forms).5

While Sunstein’s view is extreme and probably can only be applied to the most rigid and unused versions of the principle, elsewhere the principle has been accused of being unscientific and irrational, rubbery, imprecise, and counterproductive, as well as hindering progress, leading to overregulation and regulatory false positives, and placing unreasonable demands on the safety of new technologies at the expense of the benefits they might provide society.1,2,3

Especially concerning to some, the PP can be used for ideological purposes to block technologies or innovations that could save lives, attain essential goals such as the UN’s sustainable development goals, and/or combat the effects of climate change. On the other hand, proponents of the PP argue that it is consistent with the obligations we hold towards future generations, it ensures respect for human dignity, it reduces serious and irreversible environmental and public health hazards, and it facilitates people-centric progress.4,5

Potential Reformulations of the PP:
There have been several attempts to reformulate the PP to address some of the concerns leveled against it:
• Some argue that the PP is applied too rigorously and should be reserved for uncertain risks that (if realized) would be catastrophic;4
• Others argue that the PP should be used as a midlevel principle and weighed against other midlevel principles on a case-by-case basis, rather than used as an absolute rule;6,2
• Others stress the importance of context, and the consideration of trade-offs, counter-risks, and the pragmatic realization that the task is one of optimizing risk, not eliminating it altogether.11

In academia, debate about the PP has raged for decades. Everything from the principle’s logical coherence to whether there is a true referent for the term has been debated. Nonetheless, the principle is used regularly, it is present in some of the world’s foremost environmental treatises, and it is referenced in court proceedings and decision making, for which there are consequences globally. As such, it is important that stakeholders who engage with the principle are able to understand, apply, and navigate it.

Work remains to be done to clarify aspects of the precautionary principle. While some of the existing literature has revealed the thinness of the principle, it remains to be properly shown how factors such as 1) the values that orient it, 2) the chosen risk threshold, 3) what conception of science is being utilized, and 4) the response that it will trigger all influence a particular instantiation or application of the principle. Demystifying these factors would go a long way towards supporting stakeholders who must navigate the principle and its effects on policy.

Challenges with Application of the Precautionary Principle:
• European Parliament. Directorate General for Parliamentary Research Services. The Precautionary Principle: Definitions, Applications and Governance?: In Depth Analysis. LU: Publications Office, 2016.

An Assessment of the Precautionary Principle in the European Law:
• Hansson, Sven Ove. “How Extreme Is the Precautionary Principle?” NanoEthics 14, no. 3 (December 1, 2020): 245–57.

  1. Hammit J, Rogers M, Sand P, Wiener JB. The Reality of Precaution: Comparing Risk Regulation in the United States and Europe. New York: Routledge; 2010. 602 p.
  2. Goklany IM. Precautionary Principle: A Critical Appraisal of Environmental Risk Assessment [Internet]. Washington, UNITED STATES: Cato Institute; 2001 [cited 2021 Jul 5]. Available from:
  3. Second International Conference on the Protection of the North Sea: Ministerial Declaration Calling for Reduction of pollution. Int leg mater. 1988 May;27(3):835–48.
  4. United Nations Conference on Environment and Development. 1992. Agenda 21, Rio Declaration, Forest Principles. [New York]: United Nations.
  5. Sunstein CR. Laws of Fear: Beyond the Precautionary Principle [Internet]. Cambridge, UNITED KINGDOM: Cambridge University Press; 2005 [cited 2021 Jul 8]. Available from:
  6. Hansson SO. How Extreme Is the Precautionary Principle? Nanoethics. 2020 Dec 1;14(3):245–57.
  7. Sandin P, Peterson M. Is the Precautionary Principle a Midlevel Principle? Ethics, Policy & Environment. 2019 Jan 2;22(1):34–48.
  8. European Environment Agency. Late lessons from early warnings: science, precaution, innovation Summary. [Internet]. LU: Publications Office; 2013 [cited 2021 Sep 14]. Available from:
  9. Dinneen N. Precautionary discourse: Thinking through the distinction between the precautionary principle and the precautionary approach in theory and practice. Politics and the Life Sciences. 2013;32(1):2–21.
  10. European Parliament. Directorate General for Parliamentary Research Services. The precautionary principle: definitions, applications and governance: in depth analysis. [Internet]. LU: Publications Office; 2016 [cited 2021 Sep 1]. Available from:
  11. Jonathan B. Weiner. Precaution in a Multi-Risk World. Human and Ecological Risk Assessment. 2002;1509–31.

December 2021