Route Of Exposure

Allergen Exposure

The species is distributed throughout Europe, western Asia and North Africa, and has been introduced in western North America, Australia and parts of South America.

The Nettle is a fast-growing perennial reaching 1.2m wide by 1m tall. In Urticaceae, the plant grows as a large main stem with leaves in opposite pairs. Leaves are produced from March to November. The leaves are large, dark-green, triangular, coarsely toothed, and covered with poison-filled hairs. The leaves discharge their poison when touched, which results in a burning sensation and then a rash.

The reddish-brown to greenish-white flowers have no petals, are found in dangling clusters at the junction of stems and leaves, and are dioecious (individual flowers are either male or female, but only one sex is to be found on any one plant). The plant is wind-pollinated. Most Nettle species flower from April to October. The pollination mechanism is unusual: When the sun shines on the curly young flowers, the filaments become taut and eventually shoot up so quickly that the pollen is released in a puff. The small green seeds ripen from June to October.

Nettle is found in open areas and meadows, near buildings, and especially in nitrate-rich soils. Nettle has been used for salads, soups, tea, colouring, as a curdling agent, and in herbal remedies.

Clinical Relevance

Allergen description

No allergens from this plant have yet been characterised.

Potential Cross Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Urticaceae, e.g., Parietaria judaica and Parietaria officinalis. This however, does not appear to be the general case. RAST inhibition demonstrated the total absence of cross-reactivity between Parietaria and Urtica. Ramie (Boehmeria nivea), a plant of the Urticaceae family, is widely distributed in the Nagasaki area, and is known as a cause of asthma. Yet Ramie and Parietaria, examined by an ELISA inhibition test using P. officinalis and P. judaica, demonstrated no cross-reactivity.

Clinical Experience

IgE-mediated reactions

Nettle pollen frequently induces asthma, allergic rhinitis and allergic conjunctivitis.

Allergen-specific IgE to Urtica has also been detected due to occupational sensitisation.

Urticaceae pollen including both Parietaria and Urtica has been detected in large quantities in aeroallergen studies. It is reported to be the predominant pollen in northwest Spain. In Muros, Spain, pollen from this plant comprised 67% of the total aeroallergen load. The proportion of Urticaceae pollen found in Muros was the highest among all samples belonging to the Spanish Aerobiology Network. Other studies from Salamanca, Cordoba, and other parts of Spain have documented the importance of this aeroallergen in this country. Urticaceae pollen has also been reported in Italy, Poland and Switzerland.

Nettle pollen is also an important aeroallergen in England. IgE antibodies to Nettle pollen was found in 13 of 62 patients with a clinical history of summer seasonal respiratory symptoms.

Nettle pollen has also been detected in aeroallergen studies in Rochester, New York, Minnesota, Nebraska, and Texas, in Balikesir, Turkey, and in Korea.

Other reactions

Stinging Nettle can cause a wide range of cutaneous reactions, including Stinging Nettle-induced urticaria and contact urticaria following non-pollen contact with the Nettle plant. Immediate and delayed hypersensitivity reactions to the Nettle plant may also occur.

A 57-year-old woman showed symptoms of atropine poisoning after drinking Stinging Nettle tea. Belladonna (Atropa belladonna) was found on investigation to be present in the tea.