Route Of Exposure

Tarragon is a member of the Asteraceae (Compositae) family and is closely related to Common Wormwood (Artemesia absinthium), Wormwood (A. annua), Mugwort (A. vulgaris), and Sagebrush (A. tridentate). This family contains many weeds of great importance in allergy, e.g., Mugwort.

Tarragon is a perennial herb cultivated for its aromatic leaves, used as a seasoning, in salads, in the preparation of Tarragon vinegar, etc. It is a staple of French cuisine and gives béarnaise sauce its distinct flavour.

Tarragon is a perennial with stiff erect stems growing to around 1 m by 0.5 m. It has long, narrow leaves, which, unlike those of other members of its genus, are undivided. Its yellow and black flowers are small and round.

Tarragon may be found in cultivated beds or growing wild in disturbed places.

The leaves, seeds and even the stem are eaten cooked or raw. The herb is a characteristic flavourant of pickles, vinegar, béarnaise sauce, liquorice, liquors, root beer and spicy foods.

Tarragon contains up to 3% essential oil, which includes estragole. Estragole is a natural constituent of Tarragon and a number of related plants (e.g., Basil and Fennel) whose essential oils have been widely used in foodstuffs as flavouring agents.

Artemisia species are traditionally used to treat malaria, hepatitis, cancer, inflammation, and infections. Folk beliefs are borne out in that Wormwood (A. annua) and Indian sagebrush (A. indica) contain an effective anti-malarial substance artemisinin. Whether the closely Tarragon contains this substance has not been evaluated. For millennia, the Chinese used artemisinin in a tea to lower fevers. Artemisinin drugs have increasing currency in Southeast Asia and Africa.

Clinical Relevance

Allergen description

No allergens from this plant have yet been fully characterised.

Potential Cross Reactivity

An extensive cross-reactivity among the pollen of different individual species of the Asteraceae family could be expected, especially in the genus Artemesia. Species include Common Wormwood (A. absinthium), Wormwood (A. annua), Mugwort (A. vulgaris), and Sagebrush (A. tridentate). Cross-reactivity has been demonstrated in studies evaluating the pollen from this family. In one study, the in vitro cross-reactivity among 9 Artemisia species (A. frigida, A. annua, A. biennis, A. filifolia, A. tridentata, A. californica, A. gnaphalodes, A. ludoviciana, and A. vulgaris) was investigated by enzyme-linked immunosorbent assay inhibitions, which revealed strong cross-reactivity among all 9 species, with A. biennis and A. tridentata being among the strongest inhibitors. Nitrocellulose blots showed similar IgE binding patterns among the Artemisia species, with strong inhibition among all 9 extracts.

However, studies have examined only cross-reactivity to the pollen of the various members of the family, and did not examine cross-reactivity between the pollen and plant tissue of species, or between plant tissue of various members of the family. If a common protein were present between the pollen and plant leaf, then cross-reactivity similar to that between Mugwort and other pollen or between Mugwort and plant foods could be expected, as described in the case of Mugwort-Birch-Celery-spice syndrome.

Clinical Experience

IgE-mediated reactions

Tarragon may uncommonly induce symptoms of allergy in sensitised individuals. Although reactions may be rare, they may also often be overlooked.

Allergy to the pollen of Wormwood (A. annua) is considered to be one of the most important allergies in autumnal hay fever in China, just as Ragweed allergy is in North America. Considering the close family relationship and high cross-reactivity between members of this family, it is possible that allergy to Tarragon pollen also occurs and may have been overlooked.

Other reactions

A recent statement advised consumers to reduce their intake of foods containing estragole and methyleugenol, e.g., Tarragon, Basil, Anise, Star Anise, Jamaica pepper, Nutmeg, and lemon grass as well as bitter and sweet Fennel fruits. This advice was based on experiments with rats and mice where estragole, a natural ingredient of Fennel fruits, proved to be carcinogenic. However, a multicomponent mixture such as Fennel tea contains various antioxidants known to be protective against cancer. These differences were not considered in the risk assessment.

Considering the long traditional use of Fennel tea and the total lack of epidemiological and clinical studies indicating a credible cancerogenic potential, the probability of a serious risk connected with the consumption of Fennel tea seems to be negligibly small.