Yushō disease (油症?) (literally oil disease) was a rare condition which occurred in northern Kyūshū,Japan in 1968. The condition resulted from the persistent pollutants polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) with which rice oil was contaminated. About 2000 people were affected in Japan. Symptoms included dermal and ocular lesions, irregular menstrual cycles and a lowered immune response. Other symptoms included fatigue, headache, cough, and unusual skin sores. Additionally, in children, there were reports of poor cognitive development.
There have been studies undertaken on animals to understand the mechanisms of PCBs and PCDFs and their effects. Scientists discovered that low levels of PCB's could kill fish and other wildlife and as such their use in manufacturing was reduced.