Pollen and pollen counts

Pollen is the male component of the plant reproductive system. The type of pollen that most commonly causes allergic reactions comes from plants that produce small, light, dry pollen granules in large quantities that can be carried through the air for miles. Common allergenic culprits include:

• Hardwood deciduous trees such as oak, ash, elm, birch, maple, alder and hazel, as well as hickory, pecan, and mountain cedar. Juniper, cypress, and sequoia trees also are likely to cause allergies.
• Grasses such as timothy grass, Kentucky bluegrass, Johnson grass, Bermuda grass, redtop grass, orchard grass, sweet vernal grass, perennial rye, salt grass, velvet grass, and fescue.
• Weeds such as ragweed, sagebrush, redroot (pigweed), lamb's quarters, goosefoot, tumbleweed (Russian thistle), and English plantain. Ragweed is the dominant weed pollen in the eastern and midwestern United States.

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In the spring, hay fever is caused by pollen from trees. Over the summer, pollen from grasses and weeds are the culprits. In the fall, ragweed is usually the cause of hay fever.

The beginning and end of pollen seasons for particular plants is very consistent in each geographical region. However, the weather can determine how heavy the pollen count will be seasonally and daily. The pollen count is a measure of the amount of pollen in the air. Usually, pollen counts are at their highest on warm, dry, and breezy mornings and their lowest on rainy, cool days. Generally, the severity of your allergic reaction will mirror the rise and fall of the pollen count.

Pollen counts commonly are included in local weather reports. The counts usually are reported for mold spores and three types of pollen: trees, grasses, and weeds. The count is reported as grains of pollen per square meter of air collected over 24 hours. This number represents the concentration of all the pollen in the air in a certain area at a specific time.

In general, a "low" pollen count means that only people extremely sensitive to pollen will experience symptoms. A "medium" count means many people who are sensitive to pollen will experience symptoms, and a "high" count means most people with any sensitivity to pollen will experience symptoms.

Although the pollen count is approximate and fluctuates, it is useful as a general guide when you are trying to determine whether or not you should stay indoors to avoid exposure to pollen.