Despite the various effects on the health of Chamaecyparis obtusa essential oil (COEO), an adverse effect on the skin has recently been reported. Therefore, in this study, the skin sensitization test of COEO was conducted to confirm the skin safety of the essential oil by the guinea pig maximization test. Guinea pigs were sensitized with intradermal injection of 0.1ml COEO for 24 h. After 1 week, 5% of COEO was treated on the site of injection and 2% of the essential oil was challenged 2 weeks later. The average skin reaction evaluated by erythema and edema on the challenge sites and sensitization rate in the COEO-treatment group at 24 h were 0.0 and 0%, respectively, which are substantially low compared with in the 2,4-dinitrochlorobenzene-treatment group (positive control group) (average skin reaction: 3.0, sensitization rate: 100%) and identical with in the olive oil-treatment group (negative control group), representing a weak sensitizing potential. The average skin reaction and sensitization rate observed at 48 h were 0.0 and 0% in the COEO-treatment group, respectively, and 2.0 and 100% in the positive control group, respectively. It was concluded that 5% of COEO classified to Grade I, induced no sensitization when tested in guinea pigs.

This study was carried out to investigate the acute oral toxicity of Chamaecyparis obtusa (C. obtusa) essential oil (CBE) in New Zealand white male and female rabbits. Acute oral treatment with the CBE did not reveal any sign of toxicity or mortality in treated rabbits. The body weight of the rabbits was not affected after a single oral administration of the CBE during the 14-day observation period. In both the hematological and blood biochemical analysis, all parameters of the treated group with 2,000 mg/kg body weight of the CBE were not significantly different than those of the control group. Therefore, the lethal dose 50 of the CBE was estimated to be greater than 2,000 mg/kg body weight in rabbits, which indicated that the CBE is non-toxic. In conclusion, this study suggests that oral administration of the CBE is safe on rabbits.

The present study was carried out to investigate the acute oral toxicity of Chamaecyparis obtusa (C. obtusa) essential oil in ICR male and female mice. Acute oral treatment with C. obtusa essential oil did not reveal any sign of toxicity or mortality in treated mice. Mouse body weights were not affected after single oral administration of C. obtusa essential oil during the 14-day observation period. In the hematological and blood biochemical analysis, all parameters of the treated group with 2,000 mg/kg body weight of the essential oil were not significantly different those of the control group. Therefore, the lethal dose 50 of the essential oil was estimated to be greater than 2,000 mg/ kg body weight in mice, which indicated that the essential oil is non-toxic. In conclusion, this study suggests that C. obtusa essential oil orally safe ICR mice.