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Pollen is the male gamete (microspore) of seed plants, carried from plant to plant by wind (anemophilous plants) or insects (entomophilous plants). Medical interest in these structures stems from the prevalence of pollen allergies. It is estimated that 15% of the population is allergic to pollen from anemophilous plants [3], and symptoms can affect virtually any organ [4]. Methods of measuring pollen concentration in atmospheric air could be roughly divided into gravimetric, as well as inertial passive and impaction methods. Inertial impaction methods, called also volumetric, are most useful as they allow to measure the number of pollens in a specified volume of the air. Methods of detecting pollen allergens that are not bound to pollen grains were also presented. Finally, the usefulness of pollen monitoring was discussed for doctors who treat patients with pollen-allergic rhinits, asthma, airborne atopic eczema and contact urticaria. Key words: allergology, pollinosis, pollen allergy, pollen monitoring, allergic rhinitis, asthma, airborne dermatitis, airborne urticaria. |
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The potential pathogenic effects of plant pollen were first noticed by Bostock, and then in the 19th century by Blackley, who was the first to perform skin tests. He also assessed pollen concentration in the air using the inertial method, using four vertically arranged microscope slides coated with a sticky substance, each facing a different direction [2]. Regular research on the problem of pollen allergy began at the beginning of the 20th century, when a new field of medicine - allergology - was established. These issues were introduced to Poland by a Krakow dermatologist, Professor Mieczyslaw Obtułowicz (1902-1970), who in 1939 published the first article on pollinosis in the Polish medical literature [29]. The development of aeropalynology for medical purposes from this pioneering publication until the 1990s is presented in a separate article [40].
Currently, pollen monitoring plays an important role in allergology. Pollen reports are a precise and important tool for allergists. Measurement points, centered around the Environmental Allergen Research Center and research institutions, provide reliable data for every region of Poland [34]. Information for patients and physicians is distributed through newspapers, radio and TV stations with local and national coverage. Due to the high prevalence of pollen allergies, aeropalynology receives significant attention in allergist training programs.
Methods for measuring pollen concentration in the air can be divided into gravimetric, and inertial [16].
Gravimetric (sedimentation) methods involve exposing horizontally arranged microscope slides coated with a sticky substance to the surface for a specified period of time, on which pollen particles settle under the influence of gravity. This method is very simple to perform, and a formula has been developed that can be used to calculate the amount of pollen in the air from the number of pollen particles on the slide (Omeliansky's formula) [11], but it does not work well in case of moving air.
Inertial (impact) methods can be divided into passive (pollen moved by wind) and forced-flow methods. In the latter, the flow of a constant volume of air is forced by a vacuum pump, and pollen particles entering the airflow adhere to a sticky surface. Only forced-flow methods allow for volumetric measurement, meaning they measure the actual number of pollen grains in a given volume of air; for this reason, they are also referred to as volumetric methods.
In 1952, Hirst developed a practical automatic apparatus for volumetric measurements (volumetric spore trap) [18]. A modification of Hirst's apparatus was the Kramer-Collins spore sampler, which allowed for the measurement of pollen concentration with an accuracy of 1 hour. The Burkard apparatus, in which the daily replaced microscope slide was replaced by a plastic tape on a drum changed every 7 days, and the Lanzoni apparatus [16, 20] were also based on Hirst's solution. In all these methods, a transparent material with adhered pollen is viewed under microscopic magnification by a botanist, who identifies pollen based on its morphology and calculates its concentration per unit volume of air [3].
Volumetric measurements are conducted using stationary devices, therefore providing information on the average pollen concentration in a given area. However, they do not take into account the fact that a specific patient may be exposed to significantly higher pollen concentrations during their daily commute, for example, by passing a garden or park. Individual exposures can be identified using individual measurement devices, which sample air from the patient's immediate surroundings for pollen analysis [23]. Such individual analyses are time-consuming and expensive, so they are only used in exceptional cases, primarily for research purposes.
Due to the fact that up to half of the amount of pollen allergens in the air may not be bound to pollen grains, devices and methods have also been introduced to measure the concentration of allergens in the air rather than pollen grains, e.g., bioaerosol samplers with particle size division; the allergen concentration in individual fractions is then determined using the ELISA method [33]. Instead of a sticky layer on a transparent material, water washers are used, in which the airborne allergens dissolve [41]. These methods, although very promising, are expensive and require further evaluation of their usefulness.
Because vegetation periods change from year to year, so-called pollen calendars are only indicative [14, 39]. When interpreting pollen reports, it should be remembered that pollen concentration is most often reported as the average concentration of pollen grains in 1 m3 over a 24-hour period. This value does not reflect the fact that pollen concentrations may be much higher at certain times of the day [20]. Furthermore, the reported values reflect pollen concentrations in the immediate vicinity of the device. It should be remembered that local topography (presence of trees, tall buildings, etc.) has a significant impact on the measurement results [30, 31], and within a single city or even district, enclaves with particularly high or low pollen concentrations can be found [35].
An allergist undertaking pollen allergy diagnosis and desensitization must be familiar with the flora of their region. A physician lacking this knowledge, misled by cross-reactivity between pollen from different plant species, may conduct skin tests or even immunotherapy with pollen allergens not found in the given area [20]. This situation poses a real threat to patients. Responsibility for the safety and health of patients with pollinosis also rests partly with the botanist who communicates pollen analysis results to physicians and patients. Analyses must be reliable and take into account possible sources of error, such as the morphological similarity of pollen from certain plants (e.g., birch, common hornbeam, bay laurel, and common hackberry) [20]. Therefore, it is essential to monitor the quality of the tests, for example, by regularly assessing control preparations.
The sensitizing potential of pollen depends on the quantity and structure of antigens and their water solubility [45]. An additional factor influencing the sensitizing potential of pollen is environmental pollution. Ruffin et al. demonstrated that sulfur dioxide, nitrogen dioxide, and carbon monoxide enhance the sensitizing effect of pollen [37]. Diesel exhaust [9, 19], particulate matter [25, 28], and ozone [21] also contribute to sensitization to plant pollen.
The relationship between pollen concentration of anemophilous plants and the severity of symptoms in allergic rhinitis patients is very well documented [13, 43]. However, it has long been clear that determining the threshold pollen concentration above which the symptomatic period can be recognized in allergic individuals is very difficult, due to high variability in individual sensitivity to allergens [27]. Davies and Smith found that in some already sensitized patients, 20 grass pollen grains in 1 m3 were able to provoke rhinitis symptoms, but a concentration of 50 grains/1 m3 was necessary to induce symptoms in all patients [8]. Viander and Koivikko demonstrated that in 90% of birch pollen-sensitized patients with allergic rhinitis, a concentration of 80 birch pollen grains in 1 m3 was necessary to induce symptoms at the beginning of the pollen season, whereas later only 30 grains/1 m3 was sufficient to maintain symptoms [44]. They confirmed Connell's earlier observations that the amount of pollen required to induce nasal mucosal swelling is significantly lower during the pollen season than outside of it [6]. This phenomenon, known as priming, involves an increased sensitivity to pollen allergen following prior specific (allergen) or non-specific irritation (e.g., ammonia) [1]. However, some researchers did not observe the priming phenomenon in patients [15].
It should be emphasized that threshold values vary among plant species, due to differences in the structure and composition of pollen grains. For example, a concentration of 200 ragweed pollen grains in 1 m3 is considered very high, causing symptoms in all allergic individuals. However, the same concentration of cedar pollen will not trigger a reaction, and only approximately 10,000 cedar grains in 1 m3 can trigger a respiratory reaction [20].
The pathomechanism of asthma induced by pollen from anemophilous plants has long remained unclear due to the fact that the large size of pollen grains prevents their penetration into the lower respiratory tract. It was commonly believed that particles with an aerodynamic diameter exceeding 10 μm were retained in the upper respiratory tract, while pollen grains have a diameter of 20-100 μm [10]. Using scintigraphy techniques, Wilson et al. demonstrated that radiolabeled meadowgrass (Poa pratensis) pollen settled primarily in the nasopharynx and stomach, but they did not detect an increase in radioactivity in the lungs [46]. Nevertheless, it was possible to detect individual pollen grains in bronchial secretions [24]. The detection of pollen antigens in the fraction of particles with a diameter smaller than 1 μm was significantly more important for understanding pollen-induced asthma [17, 38, 42]. It has been shown that during rain, pollen grains disintegrate under the influence of osmotic forces, releasing small starch particles containing allergens that can easily penetrate the lungs [22]. Up to 50% of the total allergen amount may be bound to particles smaller than pollen grains [36]. The discovery of the role of external factors in allergen release helps to understand the subsequent observation that the concentration of allergens associated with the small-molecule fraction does not correlate with the number of pollen grains at a given moment [32, 33]. Furthermore, the ability has been demonstrated of airborne particles originating from other birch parts, such as leaves or buds, to bind birch pollen-specific IgE [12]. Therefore, it seems that the current pollen concentration does not directly affect the condition of patients with pollen-induced asthma at a given moment, and it is necessary to take into account additional factors, such as rainfall or other atmospheric phenomena.
In a group of patients with atopic dermatitis, seasonal exacerbations were observed, coinciding with pollen season. These exacerbations were most severe on exposed body parts (face, hands, and neck). Prick and patch tests to pollen allergens were generally positive in these patients [5, 7]. This form of atopic dermatitis is called airborne atopic dermatitis. Cases of airborne contact urticaria induced by pollen have also been described [26]. Care for patients with eczema and airborne urticaria also requires physicians to use pollen monitoring. Because the problem of contact allergy to plant pollen has only recently come to light, more questions remain unanswered in this field than in the case of respiratory allergies.
Common sense suggests that the higher the pollen concentration in the air, the more allergen is deposited on the skin. However, data on pollen deposition on the skin are currently lacking. Perhaps a more appropriate monitoring method for patients with airborne dermatitis would be the sedimentation method: Unlike the respiratory tract, which is a flow-through system, the skin is a surface on which airborne particles settle due to gravity and viscosity, among other factors. Regardless of the questions that remain to be answered, the previously mentioned evidence of exacerbations of skin lesions during the pollen season strongly indicates on the usefulness of pollen monitoring in airborne atopic dermatitis with pollen allergy.
Pollen monitoring is an essential tool in diagnosing and monitoring the effectiveness of pollen allergy treatment. Proper care for patients with pollen allergies requires physicians to demonstrate not only the ability to use pollen signals but also knowledge of local flora and climatic conditions.
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Document created: 26 October 2003, last updated: 29 June 2026.