One of the most obvious features of pollen allergy is its seasonal nature - people experience its symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and day - and therefore on geographical location - rather than on the weather. (On the other hand, weather conditions during pollination can affect the amount of pollen produced and distributed in a specific year.) Thus, the farther north you go, the later the pollinating period and the later the allergy season.

In general, hewer are the seasonal times and trigger of pollen allergies.

Winter-Early Spring: Trees

Late Spring through Summer: Grasses

Late Summer through Fall: Weeds

Year Round: Dust, Mold, Pets, Insects (house hold items)

A pollen count - familiar to many people from local weather reports - is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is expressed in grains of pollen per square meter of air collected over 24 hours. A pollen count is an approximate and fluctuating measure, but it is useful as a general guide.

Pollen counts tend to be highest on warm, dry, breezy days and lowest during chilly, wet periods. Moreover, the pollen concentration in an area can be changed by population growth, land use, tree plantings and cutting, industrialization, and pollution.