Pollen Count and Allergies

Knowing the peak pollen season in your area and tracking daily pollen counts enable you to minimize your pollen exposure and reduce your allergy symptoms. Local and regional pollen and mold counts — which measure the amount of airborne allergens — are often broadcast along with local weather.

What Does the Pollen Count Mean for Your Allergies?

When you hear or read about the daily pollen or mold count, it's yesterday's count. It represents the pollen or mold samples taken during the previous 24 hours. Pollen and mold counts are usually reported as low, moderate, high, or very high. These represent your risk of developing allergy symptoms. So if the pollen count is high, you have a high chance of having symptoms if you're allergic to pollen.

The number reported as the daily pollen count represents the average number of grains of each type of pollen, as well as the average total number of pollen grains per cubic yard of air sampled in a 24-hour period. The same measurement is true for the less commonly reported mold spores. Because these numbers are averages, your actual pollen and mold exposure may be greater, depending on the time of day you're exposed. For instance, grasses only release their pollen in the morning from about 6:00 a.m. to 10:00 a.m.

Generally, the higher the count for your allergens, the greater your risk of developing allergy symptoms if you're exposed. However, it isn't absolute. Your allergy symptoms may also be affected by recent exposure to other allergens, the intensity of the exposure, and how allergic you are to the various allergens.

Use your local or regional pollen or mold count as a general guide. Be aware that weather can greatly affect pollen and mold counts. Air temperature, wind speed, and humidity all affect how much pollen and mold is airborne at a particular moment. When interpreting your local daily pollen or mold counts, keep in mind the following:

• Hot, dry, windy days generally mean more pollens and molds are in the air. Pollen levels tend to be lower on rainy, cloudy, or windless days.
  
  
• Rain tends to wash pollens out of the air. Smaller raindrops are more efficient at cleansing the air than larger droplets. Therefore, a gentle, prolonged rain shower tends to wash out more pollen than a brief, intense thunderstorm. In fact, thunderstorms can actually stir more pollen into the air.
  
  
• Peak pollen times for many grasses tend to be early morning or early evening. Peak pollen release for other plants tends to be midday and afternoon. Generally, at ground level, the peak pollen count is between 8:00 a.m. and 12:00 p.m. and again between 5:00 p.m. and 9:00 p.m.
  
  
• Pollen counts fall during times of higher humidity and rise during low humidity. When the humidity goes up, pollen grains absorb moisture, which makes them heavy enough to fall to the ground. During low humidity, water evaporates from the pollen grains, making them lighter and more easily airborne.
  
  
• The warmer the temperature, the greater the pollen. Warmer air encourages pollination. Colder air discourages pollen production.

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Written by Karen Serrano, MD
Emergency Medicine resident at the University of Wisconsin-Madison.

Reviewed by Lisa V. Suffian, MD
Instructor of Clinical Pediatrics in the Division of Allergy and Pulmonary Medicine at Saint Louis Children's Hospital, Washington University School of Medicine
Assistant Clinical Professor in the Department of Pediatrics at Cardinal Glennon Children's Hospital, Saint Louis University
Board certified in Allergy and Immunology

Last updated June 2008