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Code: t12
Latin name: Salix caprea
Source material: Pollen
Family: Salicaceae
Common names: Willow, Goat willow, Great sallow, Pussy willow

The family: Salicaceae contains the genera Populus (Aspens, Cottonwoods, and Poplars) and Salix (Willow)

Allergen Exposure

Geographical distribution
The family Salicaceae contains the genera Populus (Aspens, Cottonwoods, and Poplars) and Salix (Willow). The genus Salix, which contains around 400 species of deciduous trees and shrubs, comprises Willows, sallows and osiers (1). They are found primarily on moist soils in cold and temperate regions of the Northern Hemisphere. Most species are known as Willow, but some narrow-leaved shrub species are called osier, and some broader-leaved species are called sallow. Some willows (particularly arctic and alpine species) are low-growing or creeping shrubs (2).

Willows are cool-climate trees and are common in most of Europe, North America, western temperate Asia, and northeast Africa. In eastern Asia they are replaced by related species. The tree is uncommon in the tropics.

Willow is a deciduous shrub or small tree, usually attaining between 3 m and 15 m in height. It may grow in the form of a large and upright shrub or a multi-stemmed small tree. The bark is yellowish-brown, becoming dark brown as the tree grows older. The green leaves are oblong and irregularly toothed.

Willow is among the first trees flowering in spring. The flowers are dioecious (individual flowers are either male or female, but only a single sex is to be found on any one plant) and appear in catkins. The male Willow produces white, 2.5 – 5 cm-long flowers on a bottlebrush-like catkin. The catkins are produced early in the spring, often before the leaves, or as the new leaves open. Pollination is by insects.

The fruit is a small, cylindrical, beaked capsule containing numerous tiny (0.1 mm) seeds. The seeds are furnished with long, silky, white hairs, which allow the seeds to be widely dispersed by the wind (2).

Willow occurs in wet environments, such as riverbanks and lake shores, and in drier sites where bare soil becomes available due to ground disturbance. Willow bark is used as an herb. The wood is light and firm and yields salicine (salicylates), which is used in headache tablets and muscle-pain ointments.

No allergens from this plant have yet been characterised.

Potential cross-reactivity

The family Salicaceae contains the genera Populus (Aspens, Cottonwoods, and Poplars) and Salix (Willow). Extensive cross-reactivity between the species in the genus Salix and in the genus Populus can be expected (3-4). This has been demonstrated between Cottonwood and Willow (5). Through P-K neutralisation and passive hemagglutination inhibition, moderate cross-reactivity between members of Salicaceae and of Fagales has been shown (6).

Ole e 9, a major Olive tree pollen allergen, shows 39%, 33%, and 32% sequence identity with 1,3-beta-glucanases from Wheat, Willow, and Arabidopsis thaliana, respectively (7).Whether the 1,3-beta-glucanases from Willow were allergenic was not evaluated for.

Clinical Experience

IgE-mediated reactions
Willow tree pollen can induce asthma, allergic rhinitis and allergic conjunctivitis (2,8-11). As a close relationship exists between this Willow and other species, these species, where they commonly occur, may also induce allergic symptoms (12-13).

Willow tree pollen is an important aeroallergen in many parts of the world. This has been demonstrated in Turkey and other parts of the eastern Mediterranean region (6), at the Rabka health resort in Poland (14), and in Switzerland (5). Pollen from Salix spp. was reported to play a role in allergic rhinitis in Eskisehir, Turkey (10). In another Turkish study of 614 respiratory-allergic patients, Willow, Poplar, Olive and Cypress pollens were among important inhalant allergens causing skin test positivity (6). Other aerobilogical studies from various regions in Turkey have documented the presence of Salix spp. pollens in the air (15-18).

Pollen extracts of Box elder, Willow and Hickory elicited the largest number of allergic reactions in a Missouri, USA, population skin-tested with pollen from 12 wind-pollinated tree species (7). Salix pollen was also recorded in Anchorage, Alaska (19).

Measurement of daily pollen concentration over a 6-year period in Badajoz, in southwestern Spain, demonstrated high levels of Willow pollen, along with the pollen of another family member, Populus (20). A study of the common airborne pollen allergens in the city of Salamanca, Spain, also confirmed the presence of Salix pollen in the air (21).

Willow pollen (and the pollen of the family member Cottonwood) has been demonstrated to be an important aeroallergen in Tehran, with the pollen season extending from the first week of February through the middle of October (22).

In 9 districts of northern China, the most common aeroallergens included the pollen of Willow and its family member Populus (23); the findings were similar in Seoul, Korea, where the pollen from these trees was recorded from March to May (24).

Other reactions
Phytodermatitis due to contact with Willow has been documented (25).

Anaphylaxis has been described in a 32-year-old atopic patient after the ingestion of a pollen compound prepared in an herbalist’s shop. A few minutes after ingestion, generalised pruritus, diffuse erythema, facial oedema, cough, hoarseness and dysphonia occurred. The patient was shown to be sensitised to pollens from Artemisia vulgaris, Taraxacum officinalis and Salix alba, which were found in the preparation (26).

As Willow bark contains acetylsalicylic acid, adverse reactions to the ingestion of herbal products made from Willow bark may be attributed to allergy to Willow when in fact the allergy is to acetylsalicylic acid (27).
Compiled by Dr Harris Steinman, harris@zingsolutions.com


  1. Mabberley DJ. The Plant Book. Cambridge University Press: Cambridge. 1997
  2. Wikipedia contributors, ”Willow”, Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Willow&oldid=230803533 (accessed August 14, 2008)
  3. Yman L. Botanical relations and immuno-logical cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
  4. Rackemann FM, Wagner HC. The desensitization skin sites passively sensitized with serum of patients with hay fever.
    J Allergy 1936;7:319-32
  5. Kadocsa E, Bittera I, Juhasz M Aeropollinologic and allergologic studies for the clarification of ”poplar tree hay fever” [Hungarian] Orv Hetil 1993;134(38):2081-3
  6. Segal AT, Kemp JP, Frick OL. An immunologic study of tree pollen antigens.
    J Allergy 1970;45:44
  7. Huecas S, Villalba M, Rodriguez R. Ole e 9, a major olive pollen allergen is a 1,3-beta-glucanase. Isolation, characterization, amino acid sequence, and tissue specificity.
    J Biol Chem 2001;276(30):27959-66
  8. Wuthrich B, Annen H. Pollionosis: I. Findings on the clinical aspects and the pollen spectrum in 1565 pollen-sensitive patients. [German] Schweiz Med Wochenschr 1979;109(33):1212-8
  9. Guneser S, Atici A, Cengizler I, Alparslan N.
    Inhalant allergens: as a cause of respiratory allergy in east Mediterranean area, Turkey. Allergol Immunopathol (Madr) 1996;24(3):116-9
  10. Lewis WH, Imber WE. Allergy epidemiology in the St. Louis, Missouri, area. III. Trees.
    Ann Allergy 1975;35(2):113-9
  11. Erkara IP, Cingi C, Ayranci U, Gurbuz KM, Pehlivan S, Tokur S. Skin prick test reactivity in allergic rhinitis patients to airborne pollens. Environ Monit Assess 2008 May 7. [Epub ahead of print]
  12. Weber RW. Pussy Willow. Salix discolor. Ann Allergy Asthma Immunol 2007 Sep;99(3):A4
  13. Weber RW. White willow.
    Ann Allergy Asthma Immunol 2004;92(2):A6
  14. Gawel J, Halota A, Kurzawa R, Smieszek J. Phenologic observations of the Rabka health resort in 1990. [Polish] Pneumonol Alergol Pol 1992;60(7-8):39-41
  15. Türe C, Böcük H. Analysis of airborne pollen grains in Bilecik, Turkey. Environ Monit Assess 2008 Apr 23. [Epub ahead of print]
  16. Celenk S, Bicakci A. Aerobiological investigation in Bitlis, Turkey. Ann Agric Environ Med 2005;12(1):87-93.
  17. Peternel R, Culig J, Mitić B, Vukusić I, Sostar Z.
    Analysis of airborne pollen concentrations in Zagreb, Croatia, 2002.
    Ann Agric Environ Med 2003;10(1):107-12
  18. Bicakci A, Akyalcin H. Analysis of airborne pollen fall in Balikesir, Turkey, 1996-1997. Ann Agric Environ Med 2000;7(1):5-10
  19. Anderson JH. Allergenic airborne pollen and spores in Anchorage, Alaska.
    Ann Allergy 1985;54(5):390-9
  20. Silva Palacios I, Tormo Molina R, Nunoz Rodriguez AF. Influence of wind direction on pollen concentration in the atmosphere.
    Int J Biometeorol 2000;44(3):128-33
  21. Hernandez Prieto M, Lorente Toledano F,
    Romo Cortina A, Davila Gonzalez I, Laffond Yges E, Calvo Bullon A. Pollen calendar of the city of Salamanca (Spain). Aeropalynological analysis for 1981-1982 and 1991-1992. Allergol Immunopathol (Madr) 1998;26(5):209-22
  22. Shafiee A. Atmospheric pollen counts in Tehran, Iran, 1974.
    Pahlavi Med J 1976;7(3):344-51
  23. Li WK, Wang CS. Survey of air-borne allergic pollens in North China: contamination with ragweed.
    N Engl Reg Allergy Proc 1986;7(2):134-43
  24. Park HS, Chung DH, Joo YJ. Survey of airborne pollens in Seoul, Korea.
    J Korean Med Sci 1994;9(1):42-6
  25. Poljacki M, Paravina M, Jovanovic M, Subotic M,
    Duran V. Contact allergic dermatitis caused by plants. [Serbo-Croatian (Roman)] Med Pregl 1993;46(9-10):371-5
  26. Chivato T, Juan F, Montoro A, Laguna R Anaphylaxis induced by ingestion of a pollen compound. J Investig Allergol Clin Immunol 1996;6(3):208-9
  27. Boullata JI, McDonnell PJ, Oliva CD. Anaphylactic reaction to a dietary supplement containing willow bark.
    Ann Pharmacother 2003;37(6):832-5


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.