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Whole Allergen

t2 Grey alder Pollen

t2 Grey alder Pollen Scientific Information


Whole Allergen

Display Name:

Grey alder Pollen

Route of Exposure:





Alnus incana

Latin Name:

Alnus incana

Other Names:

Speckled alder


Grey alder (Alnus incana) belongs to family Betulaceae which also consists of birch, hazel, oak, and hornbeam tree species. It is a deciduous tree that can grow up to 24 meters. Its flowering season is from February till May and sheds pollen of size 15-40 µm. It usually favors high humidity thus can be seen near riverbanks and marshy lands. This species originated from central Europe and spread to Russia, Siberia, Asia, the US and other parts of the world. Alder is one of the significant contributors for pollinosis and inducer of respiratory allergy such as rhinitis, rhino-conjunctivitis as well as bronchial asthma. The main route of exposure for this pollen is through inhalation. To date, no allergens from grey alder pollen have been characterized. But a major allergen from common alder (Alnus glutinosa) Alt g 1 has been recognized. It shows extensive cross-reactivity with major allergens from tree pollen of the Betulaceae family.



Grey alder (Alnus incana) is a deciduous, wind-pollinated tree and can age to nearly 60 years. It is small to moderate in size, with a height up to 24 meters. It is small in comparison to its peer common alder (Alnus glutinosa). It has smooth bark, which is grey and has fissures. The leaves of this tree are oval with sharp tips. Leaves are partly green and grey. It is a monoecious plant with a flowering season from February till May (1). Grey alder generally has flowering first, followed by black alder (2).


Grey alder is commonly located on rivers and lakes sides, near wet meadows and marshland areas. It usually favors high humidity and can withstand high acidity up to 3.5 to 4 pH levels without any issues. It grows at elevated areas up to 1800 meters in the Caucasus region and central parts of Europe (1).


Grey alder belongs to the genus Alnus belonging to the Betulaceae family and order Fagales, which also includes Betula (birch), Corylus (hazel), Quercus (oak) and Carpinus (hornbeam) species.

Taxonomic tree of Grey Alder
Domain Eukaryota
Kingdom Plantae
Phylum Spermatophyta
Subphylum Angiospermae
Class Dicotyledonae 
Order  Fagales
Family Betulaceae
Genus Alnus
Species Alnus Incana



Alder pollen has a size ranging from 15 to 40 µm. It has a thick ektexine layer enveloping the pores. The pore count in grey alder is around 3 to 6 (4).


Worldwide distribution

A steady rise has been seen in the number of allergies due to tree pollen in many parts of Europe. Studies have shown that about 10 to 15% of Poland's people and around 15 % in Norway suffer from pollinosis. The major contributors to pollinosis are alder, hazel, and birch trees (5).

In a study conducted from 2002 to 2005 in Croatia, pollens from the Betulaceae family accounted for 34% of the total pollen count in 864 patients with respiratory allergy such as rhinitis, rhino-conjunctivitis as well as bronchial asthma. Alder was responsible for 6% of the above count. The number of patients with polysensitization to the Betulaceae family pollen was 12.88%. The highest rate of allergy (46.22%) was found in the 31 to 50 years age-group, whereas the lowest rate of allergy (23.12%) was found in more than 51 years age groups(6).

In a study conducted in Korea in 2017, alder was the second most found tree pollen allergy in children (n=57) with allergic rhinitis or asthma. The tree pollen count of alder in Busan was 2nd highest with 4078 grains per cubic mm. The sensitization rates for alder was 35.1 percent in these children. Among these, oral allergy syndrome was found in 12.3% of the children (7).

Environmental Characteristics

Worldwide distribution

Grey alder has its origin from the central parts of Europe. It has extended to France, Russia, Caucasus, and Siberia eventually. Later it became common in Scandinavia and was found to be present in Britain also. One of its subspecies, hirsuta, has its origin from the central and northeast parts of the Asia region (1). The studies have found that alder pollen has been found to have traveled long distances from the Alps to Fennoscandia and from Belarus, Ukraine, to Rzeszow. It has also been reported in Greece (8). In Canada, it is found mainly in Alberta, British Columbia, Yukon, and the US, particularly in West Virginia, Maryland (9). Its subspecies like rugosa and tenuifolia are formerly from the northern regions of the United States and Canada(1).

Route of Exposure


The main route of exposure for grey alder pollen is through the airway (2). Alder pollen triggers allergic reaction at the concentrations of 50 grains per cubic millimetres in 24 hours (6).

Clinical Relevance

Alder pollen (a member of the Fagales order) is a significant cause of asthma, allergic rhinitis, and allergic conjunctivitis.

Allergic rhinitis (AR) and Allergic rhinoconjunctivitis (ARC)

Allergic rhinitis is a condition affecting the quality of life of the individual. It is accompanied by other conditions like asthma, otitis media, nasal polyps, sinusitis, and lower respiratory tract infections (10). A study was conducted on 88 patients with respiratory allergy (allergic rhinitis with or without asthma). Sensitization to alder allergen was tested through specific-IgE presence and skin prick testing. The results showed sensitization to alder allergen ranged from 13.6 to 25 percent of the patients (11).


In one of the Korean studies conducted in 57 patients, allergic rhinitis was seen in 98.2% of patients. The study also reported other symptoms such as allergic conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, and oral allergy syndrome in 56.1%, 42.1%, 28.1%, 24.6%, and 12.3% patients, respectively. Alder was the second most found tree pollen in patients with allergic rhinitis or asthma. The sensitization rates to alder were 35.1 percent among these patients (7).

Atopic dermatitis

Patients with atopic dermatitis might develop the disease flare-up after exposure to an allergen such as grey alder. The most common sites include areas not covered by clothes, including the head and neck region. In a study done in 125 patients with atopic dermatitis, grey alder sensitization was found in 4.8% (12).

Prevention and Therapy

Prevention strategies


Alder allergy can be reduced or avoided by staying indoors even when the pollen count is low (13).

Allergen immunotherapy

A double-blind, placebo-controlled study was conducted in 22 patients with allergic rhinitis to evaluate intranasal immunotherapy's safety and efficacy. They received immunotherapy or placebo for 4 months. Immunotherapy consisted of birch and grey alder allergens. During the pollen season, the patients who took immunotherapy showed fewer sneezing episodes and runny nose compared to placebo and these differences were statistically significant. The requirement for drug treatment was also significantly decreased (14).

Molecular Aspects

Allergenic molecules

No allergens have been characterized by grey alder (Alnus incana). But some allergens have been characterized by common alder (Alnus glutinosa). The major allergen found in alder is Aln g I (2). The molecular weight of this allergen Aln g I was estimated to be about 16 to 20 kd, which corresponds to 160 to 180 amino acid sequences (15). Aln g 2, a profilin (actin-binding) allergen, and Aln g 4 a calcium-binding allergen has been identified (16-18). The WHO/IUIS has listed the following alder allergens.


Biochemical Name

Molecular Weight (kDa)


Aln g I

Pathogenesis-related protein, PR-10, Bet v 1 family member


In the test of immunoblot done in 9 tree-pollen allergic individuals, all of them showed positive IgE binding to Aln g I (19)

Aln g 4



In a test for IgE reactivity, Aln g 4 showed positive results in 18% of the individuals with pollen allergy (20)

Biomarkers of severity

Aln g I the major allergen in alder is responsible for allergenicity (2).


Alder pollen allergen (Aln g I) shows extensive cross-reactivity with major allergens from tree pollen such as birch (Bet v I) and hazel (Cor a I) in polyacrylamide gel electrophoresis studies (6, 21). Pollens from hazel, alder, oak, beech, hornbeam and chestnut have structurally related allergens with common IgE-binding sites responsible for their cross-reactivity(22).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti


Last reviewed: November 2020

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  11. Bogomolov A. Diagnostic value of methods for alder (Alnus incana) allergen sensitization determination in people with respiratory allergy. Tuberculosis, Lung Diseases, HIV Infection. 2019:72-7.
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  16. Wopfner N, Dissertori O, Ferreira F, Lackner P. Calcium-binding proteins and their role in allergic diseases. Immunol Allergy Clin North Am. 2007;27(1):29-44.
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