Although metals are common contact allergens, clinical findings of metal contact dermatitis have varied. Such patients have subsequently become rare in Japan as gold dermatitis caused by ear piercing or baboon syndrome by broken thermometers. To evaluate such clinical findings and to determine the frequency of metal allergy, we analyzed the results of patch testing with 18 metals from 1990-2009. Nine hundred and thirty-one patients (189 men and 742 women, mean age 39.0 years [standard deviation ± 17.8]) were tested. Metals were applied on the back for 2 days, and the results read with the International Contact Dermatitis Research Group (ICDRG) scoring system 3 days after application. Reactions of + to +++ were regarded as positive. Differences of positive rates between men and women, and patients from 1990-1999 and those from 2000-2009 were analyzed with the v 2 -test. Differences were considered significant at P < 0.05. The metal to which the most patients reacted was 5% nickel sulfate (27.2%), irrespective of sex and phase. Significantly more women reacted to nickel sulfate (P < 0.01), mercuric chloride (P < 0.05) and gold chloride (P < 0.01) than men. Significantly more patients in the 1990s reacted to palladium chloride, mercuric chloride and gold chloride (all P < 0.01) than from 2000-2009. Nickel has been the most common metal allergen and mercury-sensitivity has decreased over 19 years in Japan.

In Japan, gold dermatitis due to ear piercing increased in the early 1990s, but has subsequently become rare. To evaluate this clinical finding and to determine the frequency of gold allergy in Japan, we analysed the results of patch testing with 0.2% gold chloride from 1990 to 2001. 653 patients were tested from March 1990 to December 2001. 55 patients showed a positive reaction to gold (8.4%). Significantly more women (10.2%) than men (0.8%) reacted (P < 0.005), but there was no significant difference between positive rates from 1990 to 1995 (9.2%) and from 1996 to 2001 (7.2%). Our data suggest that patients with gold allergy did not decrease in number, despite a decreased number of patients showing clinically overt gold dermatitis. Thus, gold allergy has changed from being clinically overt to becoming occult in Japan.