yusho

Yusho, also known as oil disease, is the name given to a mass poisoning outbreak that began in 1968 in western Japan after residents consumed rice bran oil contaminated with polychlorinated biphenyls (PCBs) and related compounds, including chlorinated dioxins and furans. The term yusho literally means “oil poisoning” in Japanese.

Cause and exposure

The contamination occurred during the processing of rice bran oil, with a mixture of PCBs and other organochlorine compounds entering the oil supply through industrial equipment and additives. The poisoning spread through common cooking oil used in households, schools, and workplaces, leading to widespread exposure in affected communities.

Symptoms and health effects

Clinical features varied but often began with skin changes such as chloracne, hyperpigmentation, and eye irritation. Other early symptoms included fatigue, nausea, and abdominal discomfort. Long-term exposure has been linked to liver dysfunction, neurological and developmental effects in children, immune system alterations, and an increased risk of certain cancers. Many symptoms persisted for years, and the condition spurred ongoing medical surveillance and research.

Affected population and response

Tens of thousands of people across several prefectures in western Japan were affected. The outbreak prompted epidemiological investigations, public health interventions, and compensation programs for victims. It also led to changes in food safety, industrial hygiene, and environmental health policies in Japan and contributed to global awareness of PCBs and dioxin-like contaminants.

Legacy

Yusho is one of the earliest large-scale poisoning incidents linked to PCBs and dioxins, illustrating the long-term health and regulatory implications of industrial pollutants. The event spurred protective measures, continued toxicological research, and informed responses to subsequent oil-related poisoning cases, such as the Yucheng incident in Taiwan.