No significant toxic activity has been ascribed to anise oil, which has generally been recognized as safe and is approved for food use (Lawrence Review of Natural Products, 1991). When applied to human skin in 2% concentrations in petrolatum base, anise oil produced no topical reactions, and the oil has not been considered a primary irritant. However, anethole has been associated with sensitization and skin irritation and may cause erythema, scaling, and vesiculation. Contact dermatitis reactions to aniseed and aniseed oil have been attributed to anethole (Newall et al., 1996).
Bergapten is known to cause photosensitivity reactions, and concern has been expressed over its possible carcinogenic risk (Newall et al., 1996). Reactions have been reported with products such as creams and toothpastes flavored with aniseed oil, and the oil has been reported to cause contact sensitivity, cheilitis, and stomatitis.
Ingestion of the oil may result in pulmonary edema, vomiting, and seizures in doses as small as 1 to 5 mL (Lawrence Review of Natural Products, 1991). Although anise itself is low in toxicity, the oil distilled from the herb may cause some skin irritation, nausea, vomiting, and seizures (Spoerke, 1990). According to Tisserand (1988), the oil is safe to use, whereas sensitization is doubtful or borderline. High doses can produce intoxication (Fluck, 1988).
Anise is contraindicated where there is an allergy to aniseed or anethole, and the use of aniseed oil should be avoided in dermatitis or any inflammatory or allergic skin condition. Side effects include occasional allergic reactions of the skin, respiratory tract, and gastrointestinal tract. There are no known interactions with other remedies. Anise requires the warning that external use of aniseed preparations must be restricted to the inhalation of the essential oil (German Commission E, Monograph, 1988).
Bergapten may cause photosensitivity in sensitive individuals. Excessive doses may interfere with anticoagulant and MAOI therapy. The documented estrogenic activity of anethole and its dimers may affect existing hormone therapy, including the oral contraceptive pill and hormone replacement therapy, if excessive doses are ingested. In view of the structural similarity reported between anethole and myristicin, consumption of large amounts of aniseed may cause neurological effects similar to those documented for nutmeg.
The acute oral LD/50 (median lethal dose) in rats is 2.25g/kg. No percutaneous absorption of the oil occurred through mouse skin within 2 hours. The oral LD/50 of anethole in rats is 2090 mg/kg (Lawrence Review of Natural Products, 1991) and is thus rated as a moderate acute toxin. The cis isomer of anethole is from 15 to 38 times more toxic to animals than the trans isomer (Lawrence Review of Natural Products, 1991).
Mild liver lesions were observed in rats fed repeated anethole doses (695 mg/kg) for an unspecified duration. Hepatic changes have been described in rats fed anethole in their daily diet (1%) for 15 weeks, although at a level of 0.25% there were no changes after 1 year. In therapeutic doses, anethole is reported to cause minimal hepatotoxicity (Newall et al., 1996).
The safety of aniseed taken during pregnancy and lactation has not been established; however, there are no known problems, provided that doses taken do not greatly exceed the amounts used in foods (Newall et al., 1996).
A case of poisoning is on record from the accidental admixture of the fruits of Conium maculatum, which bear some resemblance to those of anise but may be distinguished by their crenate or notched ridges and the absence of oil tubes. Moreover, they are broader in proportion to their length and are generally separated into half fruits, whereas those of anise are whole (Wood and Bache, 1883).
Occasionally (in former times more often and now very rarely), the highly toxic coniine-containing fruit of C. maculatum L., hemlock, is encountered in individual lots of aniseed. At present, almost all lots of aniseed are also contaminated with up to 1% coriander fruit (Wichtl, 1994).
Dr. Ruschenberger, U.S.N., has shown that oil of anise has a remarkable power of deodorising sulphide of potassium; a drop of the oil having entirely deprived of offensive odor a drachm of lard with which five grains of the sulphide had been incorporated.
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