Material increase in risk CASES

In English tort law, a material increase in risk is an exceptional route to proving causation where scientific uncertainty makes “but for” proof impossible. Instead of showing that the defendant’s breach actually caused the injury, the claimant shows that the breach materially increased the risk of the particular disease or injury that later occurred. The exception is narrow and mainly confined to mesothelioma claims; it is not a general shortcut in negligence.

Definition and principles

Ordinarily, a claimant must prove on the balance of probabilities that, but for the defendant’s breach, the injury would not have occurred. In a small group of cases—most prominently mesothelioma—courts accept that where science cannot identify which of several exposures initiated the disease, it is enough to prove that the defendant’s breach made a material (more than minimal) contribution to the risk of that indivisible disease. The policy aim is to avoid denying all recovery because causation cannot be disentangled at a scientific level.

Where the test applies (and does not)

• Mesothelioma (the classic exception): where multiple employers or occupiers negligently exposed the claimant to asbestos and it is impossible to prove which exposure started the disease, proof of a material increase in risk is sufficient for liability. Statute then makes a liable defendant responsible for the full loss, with contribution claims between wrongdoers.
• Other diseases and clinical claims: the courts have been cautious. Outside mesothelioma, a mere increase in risk usually does not prove causation. In many industrial-disease and clinical cases, the correct approach is material contribution to harm (where cumulative causes combine to produce a single injury), not material increase in risk.
• Wider negligence: for accidents, ordinary injuries, or where science can attribute cause, the claimant must meet the usual “but for” test (or, where appropriate, material contribution to harm). A bare increase in risk will not do.

Material increase in risk vs material contribution to harm

These are different ideas. Material contribution to harm applies where several factors together cause the actual injury (for example, cumulative exposure leading to a single, indivisible illness, or combined negligent treatment weakening a patient to the point of injury). The claimant proves the defendant’s breach was one of the causes of the harm. By contrast, material increase in risk accepts causal uncertainty about which exposure caused the harm and treats an increased risk as sufficient in the narrow category where the exception is recognised.

Common examples

• Multiple asbestos exposures over decades: several employers negligently exposed a worker; the claimant cannot show which period initiated mesothelioma. A material increase in risk suffices for liability.
• Not enough: a hospital’s delay that may have reduced a patient’s chance of recovery from a non-mesothelioma condition—courts generally require proof of actual causation (save for specific, carefully limited scenarios).

Legal implications

• Liability and apportionment: in mesothelioma, a defendant who materially increased risk is liable for the whole damage; contribution sorts out shares between defendants and their insurers. Elsewhere, the ordinary rules apply.
• Pleading discipline: be clear whether the case is a true “risk” case (mesothelioma exception) or a “contribution to harm” case. Mixing the two leads to error.
• Evidence: industrial hygiene evidence, exposure histories, and medical/epidemiological materials are central to showing that the risk increase was material rather than trivial.

Practical importance

Use this tag to signal the narrow causation exception and to steer readers to the correct test in disease and clinical claims. For claimants, build a precise exposure history and expert evidence showing a more-than-minimal increase in risk where the exception applies, or frame the case as material contribution to harm where causes are cumulative. For defendants, challenge the categorisation (is this really a Fairchild-type situation?), test whether exposures were negligent and material, and pursue contribution against other wrongdoers where appropriate.

See also: Causation; But-for test; Material contribution to harm; Mesothelioma; Fairchild exception; Compensation Act 2006; Industrial disease; Contribution between tortfeasors.