An irrational perception that one's prominent sexual body parts are withdrawing into the body and subsequently being lost. In the case of men, the concern is that their penis and testes are shrinking. For women, the focus is on the perceived shrinking of the vulva and nipples. In both cases it is a fear of the loss of masculinity or femininity followed by premature death. Koro is traditionally believed to be caused by "unhealthy sex" (e.g., masturbation or sex with prostitutes). It also thought to be caused by "tainted" foods. Koro is found in china and areas of southeast asia where chinese culture has diffused (especially vietnam, malaysia, and singapore).