Fennel is a food which may result in allergy symptoms in sensitised individuals.

NB: This plant is not to be confused with Dog Fennel (Anthemis cotula)

Fennel Allergy Test: Allergen Exposure

Fennel originated in Southern Europe, and has been used by humans since ancient times. It is also common in Britain, Ethiopia, the Middle East, the Far East, the Caribbean, and parts of South America.

It is an evergreen perennial herb growing to around 1m. There are 2 main types of fennel – both have pale green, celery-like stems and bright green, feathery foliage. The broad, bulbous base is treated like a vegetable. Common fennel is the variety from which the oval, greenish-brown fennel seeds are obtained.

Both the base and stems of Florence fennel can be eaten raw in salads or cooked by a variety of methods such as braising, sautéing or boiling in soups. The leaves can be used as a garnish or snipped into small pieces like dill. The leaves or the seeds can be used to make a pleasant-tasting herbal tea.

The plant is used as a herbal remedy, including as a gargle and an eyewash.

Yellow and brown dyes are obtained from the flowers and leaves combined. The oil may be used as a flavourant or fragrance in toothpastes, soaps, perfumery, air fresheners, etc.

Fennel Allergy Test: Allergen Description

A lipid transfer protein has been detected in fennel as well as a profilin-related allergen to Bet v 1.

Fennel Allergy Test: Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected and in fact is frequently manifested. Cross-reactivity among the members of the Apiaceae family is the cause of the pattern of positive results obtained with carrot, parsley, anise, fennel and caraway.

As fennel contains a profilin-related allergen, cross-reactivity between fennel and other profilin-containing plants is possible.

Clinical observations have also been the source of reports that in mugwort and birch pollen allergy, hypersensitivity to spices is frequently seen in association.

Fennel Allergy Test: Clinical Experience

Fennel may commonly induce symptoms of food allergy in sensitised individuals. Allergic symptoms may occur in children. Fennel allergy in children may result in symptoms of food allergy and/or atopic dermatitis.

Typical features of oral allergy syndrome (OAS) may occur with the ingestion of fennel. Among 196 birch pollen-hypersensitive patients with OAS caused by various vegetables who were examined in a cross-sectional part of a study, 195 had apple and/or hazelnut allergy, and 103 had Apiaceae sensitivity; only a single patient had Apiaceae allergy alone. Apiaceae-positive patients showed significantly higher birch pollen IgE antibody levels than did negative ones.

Food-dependent exercise-induced anaphylaxis following ingestion of fennel has been reported.

Other reactions

A survey of the literature shows essential oils of 11 plants (eucalyptus, fennel, hyssop, pennyroyal, rosemary, sage, savin, tansy, thuja, turpentine, and wormwood) to be powerful convulsants due to their highly reactive monoterpene ketones.