The respiratory tract is a very frequent site of manifestation of allergies due to its large surface area. The lungs are ventilated with about 10,000 liters of air per day, so that allergens contained in the air penetrate the respiratory tract in large numbers.
Pollen grains with a size of up to 100 µm are most likely to be trapped in the upper respiratory tract. Mite and cat allergens with a size of about 5 µm penetrate deeper into the lower respiratory tract.
For hay fever and asthma, the inhalation allergens play the most decisive role. These are tree and grass pollens, mites, molds and animal allergens.