Hayfever shouldn‘t really be called hayfever at all because it is caused by pollen not hay and sufferers rarely have a fever! Medically it is referred to as seasonal allergic rhinitis. Seasonal (because it occurs only at certain times of the year) rhinitis (meaning inflammation of the nasal membranes).
Pollens are the male reproductive part of plants and trees that fertilise other plants of the same species.
They are small grains which contain a large number of allergic proteins and are invisible to the naked eye.
The main culprits of hayfever are airborne pollens rather than those carried by insects. This is because they are very light and can be carried in the air for long periods of time, moreover they are produced in much larger numbers to overcome the wastage, as this is a less exact means of pollination.
When the pollen reaches the eyes, nose or lungs of a sensitised person, they cause the allergic reaction commonly referred to as Hayfever.
Different plants produce their pollen at different times of year and it is possible to work out which plants might be responsible for each individual‘s symptoms (see Pollen Calendar). The most common is grass pollen, which is around from late April to early September.