# Eggshell plaintiff rule

> The eggshell plaintiff rule holds the person at fault responsible for all the harm a crash causes, even to someone unusually fragile. How it works.

Canonical page: https://accidentclaimfacts.com/glossary/eggshell-plaintiff/  
Last reviewed: October 29, 2026 by the Accident Claim Facts editorial team  
General information, not legal advice. Talk to a licensed attorney in your state.

## Quick answer

The eggshell plaintiff rule, also called the thin skull rule, says that a person who causes an injury is responsible for all the harm it does, even if the injured person was unusually fragile. The person at fault must, in the words of Cornell's Legal Information Institute, "take the victim as they find them."

## In a car accident claim

The rule comes up when the injured person had a pre existing condition, such as worn spinal discs, an old neck injury, brittle bones or an illness. The insurer cannot argue that a healthier person would have walked away. California's civil jury instructions, for example, tell jurors to decide the full amount of damages even if the injured person was more susceptible to injury than a normally healthy person would have been.

The rule has limits. The at-fault driver does not pay for the old condition itself, only for the harm the crash caused, including making the condition worse. California's instructions allow damages for the effect of the crash on a physical or emotional condition that it made worse. So the dispute usually turns to causation: how much of the current problem is new. Our [injuries hub](https://accidentclaimfacts.com/injuries/) and the guide to [back and neck injuries](https://accidentclaimfacts.com/injuries/back-and-neck-injuries/) explain how medical records show that difference.

## Example

> **Example:** Two passengers feel the same jolt in a rear-end crash. One recovers from a neck strain in a few weeks. The other has osteoporosis and suffers a spinal fracture. Under the eggshell plaintiff rule, the at-fault driver is responsible for the fracture, even though a typical person would not have been hurt as badly.

## Related terms

- [Pre-existing condition](https://accidentclaimfacts.com/glossary/pre-existing-condition/)
- [Causation](https://accidentclaimfacts.com/glossary/causation/)
- [Damages](https://accidentclaimfacts.com/glossary/damages/)

## FAQ

### Does the eggshell plaintiff rule mean the other driver pays for my old injury?

No. It covers the harm the crash caused, including making an old condition worse, but not the condition you already had. Medical records from before and after the crash usually show the difference.

### Is the thin skull rule the same as the eggshell plaintiff rule?

Yes. They are two names for the same rule. Courts and lawyers also call it the eggshell skull rule.

## Sources

- [Cornell Legal Information Institute, Wex: eggshell skull rule](https://www.law.cornell.edu/wex/eggshell_skull_rule) — definition of the rule
- [Judicial Council of California, Civil Jury Instructions (CACI) 2026](https://courts.ca.gov/system/files/file/judicial_council_of_california_civil_jury_instructions_2026.pdf) — No. 3927 (aggravation of a preexisting condition) and No. 3928 (unusually susceptible plaintiff)