Pollen Allergens


Timothy | Birch | Olive | Mugwort | Wall pellitory


  g6 Timothy

Allergen description

Phleum pratense


Poaceae (Gramineae)





Timothy pollen often induces hay fever, asthma and conjunctivitis in sensitised individuals. Timothy is one of the world’s most common grasses and one of the most common sources of animal fodder. It grows best in cooler, humid climates.

A number of timothy allergenic proteins have been identified and characterised.

Allergen exposure

Timothy flowers from early summer to midsummer. Timothy is widespread in fields and meadows, and on roadsides. It is sown in pastures for forage, and is very common in hay.


An extensive cross-reactivity among different related grasses could be expected, in particular grasses belonging to the subfamily Pooideae.

Timothy grass pollen also seems to share allergens with tomato, peanut, kiwi and other fruits and vegetables. It also shares IgE binding epitopes with glycoprotein latex allergens, which might in part explain clinical symptoms in pollen-allergic patients on contact with latex.

Clinical experience

IgE mediated reactions

Allergy to timothy grass pollen has been reported widely. Timothy grass is one of the most important causes of allergic rhinitis, asthma and allergic conjunctivitis during summer in cool temperate climates.

A European Community respiratory health survey reported that adults who had lived on farms as children were less frequently sensitised to timothy grass, and were at lower risk of having nasal symptoms in the presence of pollen in general.

Timothy grass is a very prevalent aeroallergen in the Mediterranean countries, including Spain. In a birch and ragweed-free area in Spain, 97.9% of patients allergic to pollens were sensitised to timothy and rye grass. The strongest associations between bronchial hyperreactivity and specific IgE responses were seen with timothy grass.

In Sweden, in allergen-specific IgE tests on 7099 adult patients with asthma and/or rhinitis, timothy, cat and birch were the most prevalent allergens. Of these patients, 65% were sensitised against several allergens and 35% had a mono-allergy, most frequently to timothy grass (70%).



  t3 Birch

Allergen description

Betula verrucosa



A tree species producing large amounts of pollen, often inducing hay fever, asthma and conjunctivitis in sensitised individuals.

The common silver birch is a single-stemmed, deciduous tree with a height of up to about 25 metres. The bark is smooth and silvery white, becoming black and fissured into rectangular bosses.

Several birch pollen allergenic proteins have been identified and characterised, such as Bet v 1 as a major allergen and Bet v 2 as a profilin.

Allergen exposure

The birch tree flowers in late spring, usually at the same time as the leaves appear. In North America it blooms in early spring and occasionally again in late summer or fall. The bloom time is usually short. The birch trees are wind pollinated.

The birch occurs in woods, particularly where the soil is lighter. It often grows in heath lands and clearings and is also planted in gardens.

The common silver birch is native and common in most of Europe, northwest Africa and western Siberia, but rare in the southernmost parts of Europe. It is the most common tree found in Scandinavia and the Alps and a potent pollen producer in those areas. There are also closely related species in East Asia and North America.


Cross-reactivity between pollens from species within the Betulaceae family or closely related families can be expected and is often seen.

Major allergens in hazelnut, apple, pear, apricot and sweet cherry as well as minor allergens in other foods, e.g. peanut and soy, are structural homologs to the birch pollen major allergen Bet v 1.

Cross-reactivity has also been frequently observed to other substances containing profilin, e.g., hazel-nut, ragweed pollen, mango, mugwort pollen, timothy pollen, celery, carrot, peanut and spices.

Clinical experience

IgE mediated reactions

Birch pollen is highly allergenic, causing allergic reactions such as asthma, allergic rhinitis and conjunctivitis. Birch is one of the most important causes of springtime hay fever.

Cross-reactivity between birch and food may result in symptoms of Oral Allergy Syndrome in birch-sensitised individuals. Symptoms of food allergy in birch pollinosis patients are usually mild and restricted to the oral cavity. On the other hand, while allergy to a food, e.g., hazel-nut, without concomitant pollinosis is less common, symptoms tend to be more severe and are often systemic.



  t9 Olive

Allergen description

Olea europaea



Olive tree pollen often induces hay fever, asthma and conjunctivitis in sensitised individuals.

The olive tree is an evergreen growing to 10 metres, with a broad, round crown and a thick and knotty trunk.

Pollination is by insects, but also by wind when pollen is in abundance. Olives grow in plantations and woods, and as scrub in dry rocky places.

Allergen exposure

Olea europaea, the olive tree, has been recognised as one of the most important causes of seasonal respiratory allergy in the Mediterranean area and in other parts of the world where this tree is now grown.

The olive tree probably originated in Asia Minor, spread to the Mediterranean region, and was then introduced into North America (especially California and Arizona), South America (Chile), Australia and South Africa. In North America olive trees are found only in the Southwest.

The pollination period of Olea varies. It occurs in the spring, but in Europe may start as early as January, depending on the region.


A high degree of cross-reactivity has been demonstrated between olive tree, ash and privet and all members of the Oleaceae family.

In a Spanish study on Cupressus sensitisation, skin-prick tests on 1532 patients suffering from respiratory disorders (asthma and/or rhinoconjunctivitis) demonstrated that all of the Cupressus-sensitive patients also reacted positively to Olea and Fraxinus.

Due to the presence of the panallergen profilin a certain degree of cross-reactivity to other plant allergens may be expected.

Clinical experience

IgE mediated reactions

Olive pollen can induce asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals.

The frequency of sensitisation to olive tree pollen varies in the Mediterranean region. In Greece, more than 37% of atopic individuals are sensitised to Oleaceae.

The majority of studies demonstrate a higher prevalence of rhinoconjunctival symptoms than asthma. Patients are more likely to be polysensitised than monosensitised to olive tree pollen. Monosensitised individuals, children and adults, may have symptoms throughout the year without an apparent increase during the olive pollination season.



  w6 Mugwort

Allergen description

Artemisia vulgaris


Asteraceae (Compositae)

Mugwort pollen often induces hay fever, asthma and conjunctivitis in sensitised individuals.

The plant is an aggressive, coarse perennial that spreads by persistent rhizomes. It generally reaches a meter or more in height, and has a rather untidy and unattractive appearance.

Small, greenish-yellow to red-brown flower heads appear from summer to mid-autumn in clusters at the top of the plant, and produce tiny, inconspicuous yellowish-green flowers.

A number of mugwort allergenic proteins have been identified and characterised.

Allergen exposure

Mugwort is most common on rubbish heaps, roadsides, sites of demolished buildings in towns, and a variety of other disturbed situations. It is a problem weed in turf grass, nurseries, and natural areas.

The plant is native to Europe and Asia, but is now also found throughout the eastern US.


An extensive cross-reactivity among the different individual species of the genus could be expected, as well as among members of the family Asteraceae (Compositae) e.g. sage, golden rod, ragweed, chrysanthemum and camomile.

Furthermore, cross-reactivity has been demonstrated to be common between mugwort, celery, carrot and spices from the Apiaceae family (celery-carrot-mugwort-spice syndrome). There is also some cross-reactivity to lettuce, nuts, mustard and leguminoseae vegetables.

The panallergen profilin has been identified as one of the cross-reactive components in mugwort and ragweed pollen. Profilin will result in varying degrees of cross-reactivity between mugwort and other pollens and foods containing this panallergen. Profilin is found in virtually all pollens and foods of plant origin.

Clinical experience

IgE mediated reactions

Mugwort sensitisation and allergy has been reported widely. Mugwort pollen is a major cause of asthma, allergic rhinitis, and allergic conjunctivitis. Exposure to mugwort pollen may also contribute to the causation or exacerbation of the oral allergy syndrome, eczema, urticaria and anaphylaxis e.g. where pollen has contaminated a food, e.g., honey.

Approximately 25% of mugwort-allergic patients have reported subsequent hypersensitivity to a variety of foods e.g. celery, spices and carrots.



  w21 Wall pellitory

Allergen description

Parietaria judaica



Wall pellitory is a weed pollen, which often induces hay fever, asthma and conjunctivitis in sensitised individuals.

It is a sprawling, many-branched, bushy perennial weed, with brittle, reddish stems. It grows from 30 to 100 cm.

Wall pellitory is a common weed around the Mediterranean and along the West Coast of Europe, as far north as central England. It has been introduced in other parts of Western Europe and in Australia and Argentina. Two closely related species are found in the US and one in Brazil.

The genus Parietaria has about 10 species, which are highly cross-reactive to each other. Parietaria pollen allergens are one of the most common causes of pollinosis in areas where the plants grow.

Allergen exposure

The plant preferably lives on walls, rocks, banks and hedge banks.

In many countries the wall pellitory flowers all year round, but with distinct peaks in spring and around November.

Parietaria allergy is strongly associated with Mediterranean countries.


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. A high homology has been shown between P. judaica, P. officinalis, P. lusitanica and P. mauritanica.

However, for wall pellitory cross-reactivity with other family members of different genera can also be expected as well as to a certain degree to other plants due to the presence of the panallergen profilin.

Clinical experience

IgE-mediated reactions

Wall pellitory pollen has been recognised as an important allergen, causing symptoms of asthma, allergic rhinitis and allergic conjunctivitis.

Rhinoconjunctivitis and bronchial asthma, alone or in association, are the most common clinical manifestations. The season in which patients experience symptoms is prevalently spring. However, many patients show a multi-seasonal pattern.

In children, sensitisation to wall pellitory is low, but it may become the most frequent cause of sensitivity as individuals grow older.