Type:
Whole Allergen
Whole Allergen
Whole Allergen
Willow
Inhalation
Salicaceae
Salix caprea
Salix caprea
Willow, Goat willow, Great sallow, Pussy willow
Willow trees (Salix caprea) are distributed across temperate regions of Europe, North America, western temperate Asia and north-east Africa. Salix pollen is a minor to moderate allergen source causing allergic rhinitis and asthma. Willow pollen shows cross-reactivity with other members of the Salicaceae family (mainly poplars) and with beech.
Willows (Salix caprea) are cool-climate trees found commonly across most of Europe, North America, western temperate Asia and northeast Africa (1). Willow trees flower from February to May, producing pollen on catkins (a slim, cylindrical flower cluster or spike); they are both wind- and insect-pollinated (2). Peak pollen production occurs in April in the UK, with a low to medium emissions strength (3).
Taxonomic tree of Salix genus (4) |
|
Domain |
Eukaryota |
Kingdom |
Plantae |
Phylum |
Spermatophyta |
Subphylum |
Angioospermae |
Class |
Dicotyledonae |
Family |
Salicaceae |
Genus |
Salix |
Tree pollen
In a review of 36 publications of pollen allergy in the Middle East, an average of 10.9% of the study populations were allergic to willow pollen (5).
In a US study of 123 children aged 2-8 years with allergic rhinitis, willow was a significant sensitizing allergen, with the highest prevalence in children ages 2-3 years (6).
Salicaceae species are fast-growing trees used for timber production, paper, fences, shelter, nets, rope, basket-weaving, as a biomass fuel, for ornamental purposes and to control soil erosion (7). Willow is also widely used in traditional medicine and contains numerous biologically active compounds including salicilin, a pro-drug for salicylic acid (aspirin) (7).
The main route of exposure is inhalation.
Willow pollen is sampled using a volumetric trap such as the Hirst-type pollen trap (8).
Salix pollen is associated with allergic rhinitis and asthma. It has been considered a minor allergen source due to its low airborne pollen counts (3). However, in regions where willow trees are common, airborne pollen loads may be sufficient to cause significant allergen sensitization (2, 6). Salicaceae species were among the ten most allergenic tree pollens described in a review of common tree pollens in the Middle East (5). In a study of 866 allergic Turkish patients, 45.8% showed a positive skin prick test to Salix caprea (9).
Avoidance
Allergenic vegetation maps may contribute to allergy risk assessments by showing the location of willow trees at 1 km resolution. They can be combined with health data to inform allergy research, or with weather data to improve pollen forecasting or to generate pollen emission models (3).
Strong cross-reactivity between pollens has been reported, as well as moderate cross-reactivity between Salicaceae and Fagales (beech) (2)
Author: RubyDuke Communications
Reviewer: Dr. Christian Fischer
Last reviewed:January 2022