Allergic rhinitis

Allergies are caused by an oversensitivity of the body's own immune system. The immune system normally protects the organism against harmful influences such as bacteria or viruses. Allergic symptoms occur when the immune system initiates a defence reaction against substances that are actually harmless and do not cause any immune response in the majority of people. These substances are called allergens.

If a person who already has an allergy inhales an allergen (e.g. pollen or dust), the allergen comes into contact with the mucous membranes of the nose. A large number of defence cells of the immune system are located in the mucous membrane. Some of these cells recognise the allergen from earlier contact and then distribute protein substances that are specifically directed against this allergen; the correct scientific term for these is antibodies. The antibodies bind the allergen and trigger a chain of other immune reactions, in the course of which e.g. the messenger substance histamine is released. This results, for example, in a sneezing fit and itching, swelling of the mucous membranes and production of mucus, the typical symptoms of allergic rhinitis.

Examples of allergens that can be inhaled are pollen, moulds, animal hair or animal skin scales and dust mites. Normally, these are very small substances that are hardly visible to the naked eye. The plants whose pollen frequently cause allergies include:

• Trees (e. g. birch)
• Grasses
• Common ragweed (ambrosia artemisiifolia).

The amount of allergens also plays a role in triggering the allergic symptoms. Particularly high concentrations of pollen are to be found in the air in particular on hot, dry and windy days. Pollen is 'washed to the ground' on rainy days.