## Facts

- A premature infant, C, developed retrolental fibroplasia (RLF), resulting in severe visual impairment.
- Shortly after birth, C was administered excessive oxygen in an incubator by a junior doctor.
- Other factors, including C’s prematurity and existing medical conditions, were also possible causes of the injury.
- Five potential causal factors for RLF were identified, one being the negligent excess oxygen administration.
- The trial judge found the Essex Area Health Authority liable for negligence, concluding the authority had failed to prove that excess oxygen was not the cause of C's blindness.

## Issues

1. Whether the negligent administration of excess oxygen was a cause of the infant’s RLF, given multiple potential causes.
2. Whether the burden of proof concerning causation should shift to the defendant where several possible causes exist.
3. Whether it is sufficient for a claimant to show the defendant’s actions were a possible rather than a probable cause of harm.

## Decision

- The House of Lords allowed the appeal and overturned the trial court’s decision.
- It was held that no legal presumption arose to attribute causation to the defendant’s negligence where multiple independent causes existed.
- The burden of proof in negligence remained with the claimant, who had to establish on the balance of probabilities that the defendant’s breach was the likely cause of harm.
- The House of Lords differentiated this case from McGhee v National Coal Board, reaffirming that the burden of proof does not shift to the defendant unless there is a single causal factor.
- The material contribution test was found inapplicable where there are multiple distinct potential causes for the injury.

## Legal Principles

- The “but for” test is the foundational standard for causation in negligence; a claimant must show that harm would not have occurred but for the defendant’s breach.
- The “material contribution” test applies only where a defendant’s action is one of several contributing causes of the same risk, not when the causes are disparate.
- The claimant bears the burden of proving, on the balance of probabilities, that the defendant’s breach was a probable, not merely possible, cause of the injury.
- The decision distinguished circumstances involving multiple exposures to a single agent (as in Fairchild) from those involving several separate risks.

## Conclusion

Wilsher v Essex Area Health Authority [1988] AC 1074 (HL) established that when several different factors could have caused the harm, claimants must prove the defendant’s negligence was the probable cause; the burden remains with the claimant, and the material contribution test does not apply where injuries may have been caused by multiple independent agents.