Background and objective: Yusho occurred in western Japan in 1968 and was caused by ingestion of rice bran oil that was contaminated with polychlorinated biphenyls (PCBs) and dioxins such as polychlorinated dibenzofurans (PCDFs). At that time, the skin symptoms presented by patients with Yusho were at their most prominent and worst severity. Analysis of blood to determine the concentration of dioxins started in 2001 in Fukuoka prefecture, and in 2002 the examination was performed throughout Japan. There have been no reports on the relationship between blood concentration of dioxins and skin symptoms in Yusho. This is the first report to examine the relationship between blood concentration of dioxins and skin symptoms in Yusho, using statistical analyses. Methods: Using the global skin severity grade, we analyzed the change in skin symptoms, which were examined at the annual medical check-up of patients with Yusho. We also investigated the relationship between the items of the annual dermatological examination and blood concentrations of total PCDFs and total PCBs. Results: The severity of skin symptoms improved significantly in the first 20 years; nowadays, however, further improvement can hardly be observed. Using three-way analysis of variance (ANOVA), we found that of the 21 items of the dermatological examination, nine were significantly related to total PCDFs, and five were related to total PCBs. Only one item was significantly related both to total PCDFs and total PCBs. Conclusion: More than 36 years have passed since the Yusho incident, and about 60% of the patients currently present with no skin symptoms. In contrast, in about 40% of the patients, characteristic skin symptoms of Yusho, such as pigmentation of skin, black comedones and acneform eruptions, could still be observed. Our analysis of the relationship between skin symptoms and blood concentrations of total PCDFs and total PCBs proves that not only PCBs but also PCDFs have an important role in the skin symptoms of Yusho.
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