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

Walnut Allergy Test: Allergen Exposure

The English walnut (J. regia) originated in Persia, and the black walnut (J. nigra) is native to eastern North America. Today, the leading commercial producers of walnuts are the United States, Turkey, China, Iran, France and Romania. The English walnut is the most popularly consumed.

Walnuts are rich in oil, particularly in alpha-linoleic acid (omega 3 fatty acid) and linoleic acid (polyunsaturated fatty acids), and are widely eaten both fresh and in cookery.

They can be eaten directly from the shell, but more often they are eaten as an ingredient in baked goods, ice cream or other foods. They are used in salads and in meat, poultry, fish and pasta dishes.

Young walnuts are pickled in vinegar and considered a delicacy. A liqueur is made in France from the husks.

Greeks and Romans used walnuts to cure headaches, because of the shape, which resembles the two halves of the brain.

The oil is used in salads and pasta. The allergenicity of this oil and various other gourmet nut oils depends on the extraction method and the purity of the end product.
Oil paint often contains Walnut oil as an effective binding medium, known for its clear, glossy consistency and non-toxicity.

Walnut husks can produce a rich yellow-brown to dark brown dye that is used for dyeing fabric and for other purposes.

Walnut Allergy Test: Allergen Description

Several allergens present in walnut have been characterised including an albumin, a vicilin globulin, and a lipid transfer protein, all of which are major allergens, as well as a profilin and a legumin-like protein.

Walnut Allergy Test: Potential Cross-Reactivity

A high degree of cross-reactivity occurs among the different walnut species.

Early inhibition studies suggested cross-reactivity between walnut and pecan, and also with hazelnut. Cross-reactivity among walnut, hazelnut and brazil nut was reported in a patient with walnut-induced anaphylaxis.

There are reports of cross-reactivity among allergens in sesame and allergens in walnut.

Research has suggested that avoidance or restricted consumption of other tree nuts including walnuts should be recommended to peanut-sensitised individuals.

In a study of 20 patients with a clinical history of allergic reactions following the ingestion of Rosaceae fruits (apple, pear, peach, cherry, apricot, plum, or almond), 80% reported clinical reactivity to nuts (hazelnut, walnut, pistachio).

Walnut profilin may result in cross-reactivity with other profiling-containing food, but this has not been established yet.

Walnut Allergy Test: Clinical Experience

Tree nuts, including walnuts, and peanuts are frequent causes of severe food hypersensitivity and anaphylaxis.

In particular, tree nut allergies are potentially life-threatening, rarely outgrown, and appear to be increasing in prevalence.

Peanut and tree-nut allergic reactions coexist in a third of peanut-allergic patients, frequently occur on first known exposure, and may be life-threatening.

Anaphylaxis to walnut has been frequently reported. In particular, patients with an initial diagnosis of “idiopathic” anaphylaxis may have in fact reacted to walnut.

Walnut food-dependant exercise-induced anaphylaxis has been reported.

Walnut may also exacerbate atopic dermatitis.

Occupational contact urticaria from Walnut associated with hand eczema has been reported.

Other reactions

Juglone is the active ingredient of the green flesh of walnuts and is known to be a strong irritant.