As said before, these allergens are very small (invisible to the
naked eye) and very light particles that float in the
air.
Most often these allergens come in contact with the body through
inhalation, which is why they are often called inhaled allergens.
When breathed in, these particles land on the lining covering the
nose, the bronchi or the lungs, causing allergic rhinitis or
asthma. (It is the dimension of the allergens that determines where
the allergens will stop: the biggest and more heaviest particles
will be stopped in the nose while the smaller and more lighter ones
will reach the bronchi and the lung). Aeroallergens are primarily
causing respiratory allergies, such as allergic rhinitis and
asthma. However, they can also come in contact directly with the
external body surfaces such as the skin and the eye lining (eye
conjunctiva) and thus can be involved in causing atopic dermatitis,
contact urticaria or allergic conjunctivitis.
Allergens present in the outdoor and indoor air are different, even though people sensitized to different outdoor or indoor allergens can manifest similar symptoms.
You can find more information on this subject by clicking on the link Pollen Allergy in Europe, which has been specifically designed to help allergy sufferers understand more about pollen allergy, and where you will find tips on how to avoid a flare up of symptoms, and information on factors which may make it worse.