Eggshell Skull Rule
A tort principle making a defendant liable for the full extent of an injury, even when a pre-existing condition makes it unusually severe.
The eggshell skull rule holds that a tortfeasor takes the plaintiff as they find them. If a plaintiff has a pre-existing physical or psychological vulnerability that turns an otherwise modest injury into something far more severe, the defendant remains liable for the full extent of that aggravated harm -- not merely the injury an average, uninjured person would have suffered from the same conduct. The name comes from the classic hypothetical of a plaintiff with an unusually thin skull who dies from a blow that would only have bruised most people.
The rule carves out a deliberate exception to the usual foreseeability analysis in negligence. A defendant must still have owed a duty of care and breached it in a way that was a foreseeable cause of some injury to the plaintiff -- that threshold requirement doesn't disappear. But once that causal link to some harm is established, the law does not require the extent or severity of the resulting injury to have been foreseeable before the defendant is held fully responsible for it.
The core elements
Applying the rule generally requires showing that the defendant's conduct was an actual and proximate cause of some injury to the plaintiff; that the plaintiff had a pre-existing physical, psychological, or other vulnerability at the time of the incident; and that this vulnerability is what caused the resulting harm to be substantially more severe than it would have been for an average, unimpaired plaintiff. Once those elements are shown, the defendant is liable for the full, aggravated extent of the damages, not a discounted version.
What the rule does and doesn't excuse
The rule only removes the foreseeability requirement as to the severity or extent of harm -- it does not eliminate the underlying requirement that the defendant's conduct foreseeably caused some injury in the first place, nor does it apply to entirely different, unrelated harms that merely happen to follow the incident. It is also distinct from the avoidable-consequences (mitigation) doctrine, under which a plaintiff's damages can still be reduced if they unreasonably failed to seek appropriate treatment after being injured.
How it's proven and contested
Plaintiffs typically rely on pre-incident medical records and expert medical testimony to establish the pre-existing condition and to causally connect it to the disproportionate severity of the resulting injury. Defendants push back on causation directly, arguing the aggravation stems from an unrelated condition, an intervening event, or the plaintiff's own failure to mitigate rather than from the defendant's conduct. Juricratic can model an eggshell-plaintiff scenario as a dial that widens the simulated damages exposure attached to a given liability finding.
- Does the defendant need to know about the plaintiff's pre-existing condition?
- No. The eggshell skull rule applies regardless of whether the defendant knew, or could have known, about the plaintiff's vulnerability. Liability for the full extent of the aggravated harm attaches even to a completely unaware defendant, as long as the underlying conduct caused some injury.
- How is this different from ordinary foreseeability in negligence?
- Ordinary negligence still requires that the defendant's conduct was a foreseeable cause of some injury. The eggshell skull rule only removes the requirement that the severity or extent of that injury be foreseeable, so an unexpectedly serious outcome doesn't cut off the defendant's liability for it.
- Can a defendant reduce damages by pointing to the plaintiff's condition?
- Generally no as to liability itself -- the rule specifically prevents that argument. A defendant can still reduce damages on other grounds, such as showing the plaintiff failed to mitigate by seeking reasonable treatment, but not simply because the underlying vulnerability made the injury worse.
This page is an educational explainer, not legal advice, and creates no attorney–client relationship. Juricratic is a simulation engine: every probability-like figure is a dial you set, not a calibrated prediction. Verify every rule, deadline, and figure against the authorities and orders that govern your matter.
A theory is a claim path you can war-game.
Juricratic turns a legal theory into elements you can test — burdens as dials, outcomes as a distribution — so you see where the case is strong and where it breaks.
Request access →