Toxicity study of the volatile constituents of Myoga utilizing acute dermal irritation assays and the Guinea-pig Maximization test.

Myoga is a fragrant plant which is the special product of Japan and is cultivated throughout Japan. According to our earlier investigation (unpublished data) of myoga cultivators in Japan, 8 of 35 cultivators experienced contact dermatitis in the harvest season. The purpose of this study was to assess the allergenicity of myoga and its major volatile components. The volatile components of myoga were analyzed by gas chromatograph (GC). They included a-pinene, beta-pinene and R-(+)-limonene. We performed a toxicity study of each of the major fragrant components of myoga using acute dermal irritation assays and the Guinea-Pig Maximization test (GPMT) in order to probe the mechanism of allergic contact dermatitis. In acute dermal irritation assays, alpha-pinene, beta-pinene and limonene showed positive responses at concentrations of 4%; limonene oxide at 20% and myoga showed a positive response at concentrations of 100%. From the results of the GPMT, according to Kligman scores, limonene oxide was identified as an extreme skin sensitizer and myoga as a mild skin sensitizer. The results of the present study show that R-(+)-limonene is the most important allergen amongst the chemical components of myoga, and we consider it to be the reason why myoga cultivators experience allergic contact dermatitis.