Introduction: Koro is a delusion whereby a man believes his penis is shrinking into his abdomen and this may result in his death. This socially-transmitted non-neuropsychological delusional belief occurs (in epidemic form) in South-East and South Asia. We investigated whether the two-factor theory of delusion could be applied to epidemic Koro.
Methods: We scrutinised the literature on epidemic Koro to isolate features relevant to the two questions that must be answered to provide a two-factor account: What could initially prompt the Koro delusional hypothesis? Why is this hypothesis adopted as a belief?
Results: We concluded that the Koro hypothesis is usually prompted by the surprising observation of actual penis shrinkage-but only if the man has access to background beliefs about Koro. Whether the hypothesis is then adopted as a belief will depend on individual factors such as prior belief in the Koro concept or limited formal education and sociocultural factors such as deference to culture, to media, or to rumours spread by word of mouth. Social transmission can influence how the first factor works and how the second factor works.
Conclusion: The two-factor theory of delusion can be applied to a socially-transmitted delusion that occurs in epidemic form.
Keywords: Koro; delusion; hypothesis generation; suo-yang; two-factor theory of delusion.