The eggshell skull rule (or thin-skull rule) is a legal doctrine used in both tort law and criminal law that holds an individual liable for all consequences resulting from his or her activities leading to an injury to another person, even if the victim suffers an unusually high level of damage (e.g. due to a pre-existing vulnerability or medical condition). The term implies that if a person had a skull as delicate as the shell of an egg, and a tortfeasor or assailant who did not know of that condition were to hit that person on the head, causing the skull unexpectedly to break, the responsible party would be held liable for all damages resulting from the wrongful contact, even though they were not foreseeable. The general maxim is that defendants must "take their victims as they find them", a quotation from the judgment of Lawton LJ in the criminal case of R v. Blaue.
The doctrine is applied in all areas of torts - intentional torts, negligence, and strict liability cases - as well as in criminal law. There is no requirement of physical contact with the victim - if a trespasser's wrongful presence on the victim's property so terrifies the victim that he has a fatal heart attack, the trespasser will be liable for the damages stemming from his original tort. The foundation for this rule is based primarily on policy grounds. The courts do not want the accused to rely on the victim's own vulnerability to avoid liability.
The case of Smith v. Leech Brain & Co., [1962] 2 QB 405, illustrated this rule. An employee in a factory was splashed with molten metal. The metal burned him on his lip, which happened to be premalignant tissue. He developed cancer and died. The defence argued that while the burn was foreseeable, the cancer was not. However, the judges dismissed this, holding that as long as the initial injury was foreseeable, the defendant was liable for all the harm.
In 1891, the Wisconsin Supreme Court came to a similar result in Vosburg v. Putney, 80 Wis. 523, 50 N.W. 403 (Wis., 1891) (reversed and remanded for a new trial on other grounds). In that case, an 11 year old boy kicked a 14 year-old boy in the shin while at school. It turned out that the 14 year-old was recovering from a previous injury. The kick resulted in the boy entirely losing the use of his leg. No one could have predicted the level of injury before the kicking. Nevertheless, the court found that since the kicking was unlawful, and as it occurred during school and not on the playground, the 11 year-old boy was liable for the injury.
