An important external aeroallergen causing features of allergic rhinitis for sensitive persons is airborne pollen. It is a part of the plant whose primary purpose is to help plants to spread and consolidate on the soil surface. Pollen is the male part of sexual reproduction in plants, which in nature carries genetic information of the species. Pollen is known as a health enhancer, and the preparations made from it are even now used in human nutrition and medicine. For a long time, pollen has been associated only with health promotion, but alongside medical progress and deepening in the course of allergic diseases, it was noticed that these particles of plants may also have a negative impact on human health. This relates to the structure of protein in pollen and the non-typical reaction of the human body to various proteins in pollen. Some pollen is the cause of allergic rhinitis.

In Lithuania, allergic reactions can be caused by airborne pollen of birch (Betula), wormwood (Artemisia), hazel (Corylus), alder (Alnus), hornbeam (Carpinus), ash (Fraxinus), oak (Quercus), willow (Salix), ragweed (Ambrosia) genuses and pollen of the grass (Poaceae), cypress (Cupresaceae) families. In our country, people most often experience ailments during vegetation by contacting pollen of birches, wormwood, and grass plants. The nature and strength of ailments often depend on the amount of allergens in pollen.

The amount of pollen in the air in Lithuania is constantly monitored by aerobiologists at Šiauliai University. The research stations are equipped with newest specialized pollen traps. Research methods are standardized according to the requirements established by the International Association for Aerobiology. The amount of airborne pollen is analyzed for the purposes of science and presentation of allergenic situation in the air. Forecasts are provided using SILAM, MACC and other models.