Chamaecyparis obtusa (C. obtusa) is the representative tree of forest bathing, and essential oil from C. obtusa is widely used in commercial products. This essential oil contains limonene, isobornyl acetate, and terpenes, which have been reported to have anti-inflammatory, antioxidant and antimicrobial effects.
The present study was carried out to investigate the acute oral toxicity of C. obtusa essential oil in ICR male and female mice and New Zealand white male and female rabbits as well as skin and eye irritation tests of the essential oil in New Zealand white rabbits.
For acute oral treatment, C. obtusa essential oil did not reveal any signs of toxicity or mortality in both mice and rabbits. The body weights were also not affected in mice and rabbits after single oral administration of C. obtusa essential oil, during the 14-day observation period. In the hematological and blood biochemical analyses, all parameters in groups treated with 2,000 mg/kg body weight of the essential oil were also not significantly different compared with those of the control group. Therefore, the lethal dose 50 (LD50) of the essential oil was estimated to be greater than 2,000 mg/kg body weight in mice and rabbits, suggesting that the essential oil is practically non-toxic.
Skin safety study was performed to evaluate the potential toxicity of C. obtusa essential oil using the primary irritation test. From this, very slight erythema and very slight edema were formed at 24 h after application of the essential oil on the skin on abraded lesions of 3 and 1 rabbits, respectively. The primary irritation index score was estimated to be 0.17 indicating non-irritation.
For ocular irritation test of C. obtusa essential oil, the mean score was calculated across 3 scoring time points (24, 48 and 72 h after administration) for each animal for corneal opacity, iris, conjunctiva and chemosis. The mean index of ocular irritation was 2.33 and 0.67 on 24 and 48 h after treatment, respectively, and the index of acute ocular irritation of the essential oil was 2.33, indicating minimally irritant substance.
In conclusion, this study suggests that C. obtusa essential oil is orally safe, not irritant to skin and minimally irritant to eye.