Research on Epidemiology of Metal Sensitization in Japan.

BACKGROUND: Various diseases are induced by allergic reactions to metals, among which nickel, cobalt, and chromium are representative examples. OBJECTIVE: To investigate sensitization to these metals in Japan from April 1990 to March 2025. METHODS: A total of 1985 patients were patch tested with nickel sulfate, cobalt chloride, and potassium dichromate. Reactions ranging between + and +++ by the International Contact Dermatitis Research Group scoring system at day 3 or 7 were regarded as positive. RESULTS: Positive rates to nickel, cobalt, and chromium were 26.1%, 9.0%, and 4.9%, respectively. Significantly more women positively reacted to nickel than men, and there was an overt tendency toward a higher rate in the younger age group. 62.1% of cobalt-positives also reacted positively to nickel, and the positive rate to chromium decreased throughout 35 years. CONCLUSION: Accessories such as ear piercing (wounded skin) continue to play an essential role in nickel sensitization among young women. The high positive rate of nickel and cobalt co-sensitization suggests a potential synergy in immune activation. On the contrary, the decrease in chromium sensitization correlates with decreased use of cement and reduced exposure sources, such as decreased use in leather tanning. The challenge facing both Japan and the US is to reduce nickel sensitization following the successful European Union's regulations model.