Culture-bound syndromes are defined as a physical and/or mental affliction that is only recognized as a disease in a specific society or culture.
Koro is a mental illness that results in the acute fear and sensation of one’s penis retracting into one’s body. It is particularly common China, Malaysia, and Indonesia. While this syndrome exists in some form in other cultures, the characteristics of Koro make it unique to this region. Because fertility, procreation, sexuality, and the balance of male and female energies are so central (and anxiety-provoking) in these cultures, the fear of Koro being fatal is very real.
It is certainly true that genital shrinkage can occur in many different emotional or physiological states. The most provoking of these seem to be anxiety, stress, and cold. According to an article in Medical Daily by Nikki Tucker, People in these regions tend to be informed about their own physiological development through explanations allowed and accepted by their cultures. This may explain why individuals who are otherwise healthy and mentally stable believe they are experiencing Koro.