Microscopic grains produced by plants in order to
reproduce. Each plant has a pollinating period. These can vary depending
on the plant, climate and region. See also the ,
pollen pages for more information on the main pollens involved in
A hypersensitive reaction to pollen. While are generally the most common cause of (seasonal allergic rhinitis), other pollen types are also important.
These include pollens such as ,
and , and weed pollens such
and . The relative importance
of the kinds of pollen that can cause hay fever varies between different
climatic and vegetation zones. For example,
pollen, although very common in North America, is present in Europe only
in the French Rhône valley and some areas of Eastern Europe, while
the pollen most associated with seasonal allergy in Mediterranean regions
is the tree. A person allergic
to one pollen is generally also allergic to members of the same group
or family (e.g. Betulaceae ).
Pollen induced reactions include , and .