Tarragon oil is seven to eight tenths estragole, which is what gives it the aniseed smell.^[1] That is also the problem. Estragole damages DNA in rodent liver studies and is treated as a genotoxic carcinogen.^[2] It forms reactive fragments once the body processes it, and the concern is repeated or heavy exposure rather than a single use.^[2] It is an oil to use rarely, in low dilution, and to avoid in pregnancy and with children.^[2]