Aniseed toxicity and allergy information

Aniseed contains anethole and estragole which are structurally related to safrole, a known hepatotoxin and carcinogen. Although both anethole and estragole have been shown to cause hepatotoxicity in rodents, aniseed is not thought to represent a risk to human health when it is consumed in amounts normally encountered in foods. Anise and oil of anise are generally regarded as safe for human consumption.

The toxicity and cancerogenity of anethole are controversial. Anethole has two isomers (trans and cis), the cis (Z) isomer being 15-38 times more toxic to animals than the trans (E) isomer. The major component of the natural volatile oil of anise (80-96%) is trans-anethole, which is most likely non-cancerogenic. Trans-anethole will be accompanied by cis-anethole (maximum 0.3-0.4%), which is not caused by distillation, but exists naturally in anise seeds. In case of storage without protection of daylight the forming of cis-anethole is possible. Synthetic trans-anethole contains higher quantities of toxic cis-anethole compared to natural trans-anethole and therefore it is not used in food processing. Cases of intoxication with the volatile oil of anise are not known. Current United States Pharmacopeia (USP) and Food Chemical Codex (FCC) specifications for anethole do not require differentiation between the isomers.

Aniseed may cause an allergic reaction. It is recommended that the use of aniseed oil should be avoided in dermatitis, or any inflammatory or allergic skin conditions. Patients with an allergy to pollen are often suffering from spice-allergy like celery, carrot, etc. Skin-prick tests with anise extracts in several cases result in positive allergic reactions.

When consumed in sufficient quantities, anise oil may induce nausea, vomiting, seizures and pulmonary edema. Contact of the concentrated oil with skin can cause irritations. Anethole has been reported to be the cause of dermatitis (erythema, scaling and vesiculation) in some people. Compared with star anise however, the sensitization effect of anise oil is lower.