The fine dust in a flower that fertilizes other plants of the same type is pollen. It is the male part pf the plant, equivalent to an animal's semen, and is carried in the wind or picked up on the legs of foraging bees and butterflies, and finally lands on the stigma, or female part, of the plant. When pollen blows into the eyes and nose of susceptible people, it sets off an allergic reaction.
The antibodies triggered by this reaction stick to the immune mast cells. This causes the mast cells to release inflammatory chemicals, which lead to hay fever symptoms. The pollen that causes asthma or hay fever is not, despite the name, from hay at all but from grasses, trees, flowering plants and fungi. In Australia, New Zealand and south Africa, grass and tree pollens are the most common source of allergens.
Allergies are not just confined to flower pollen, pollen from pines, elm, ash, birch, oak, plantain, sorrel and nettle can also trigger an attack. Similarly, the season is not just confined to the summer months. Pollen from orchards of apples or plums can trigger hay fever among the local population and it is a known fact that florists frequently develop allergies to their products.
In cooler climates, hay fever tends to be a little more common in towns and cities than in rural areas. For example, in Scandinavia it is more common in the towns, and the same is true in other parts of northern Europe and in Eastern Europe. Italians are twice as likely to suffer from hay fever if they live in a city rather than the countryside. But in dry, arid countries, the reverse tends to be true.
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