Pollen Count

Generally, the pollen season can be subdivided into three distinct seasons, each of which can affect different people. Early spring is when trees pollinate. Grasses pollinate during the summer, and weeds pollinate late summer into the fall. In Colorado, trees generally begin pollinating in February and continue through June. Grass pollen season runs from early May through August, and weed pollen is in the air from July through September.

Pollen counts can vary widely from day to day depending on weather conditions. Generally, pollen levels increase on warm, sunny days. Windy days also commonly have higher pollen levels. Rain washes pollen out of the air, reducing pollen counts. Cool, damp weather also tends to keep pollen levels low.

National Jewish Health monitors pollen levels at its main health campus in Denver, Colorado. On weekday mornings, a technician retrieves a slide from a Burkard pollen and spore sampler. The slide is covered with a sticky substance to which pollen grains have adhered during the previous 24 hours. The technician then stains the slide, puts it under a microscope, and identifies and counts pollen grains to determine what kind and how much pollen is in the air.

The resulting pollen count is then distributed to various National Jewish Health physicians, the National Jewish Health clinical research unit, the local media, and it is also posted here on the website.

The pollen counts help inform physicians’ discussions with their patients about allergies and symptoms. They are used by clinical researchers at National Jewish Health who are evaluating potential allergy medications. The pollen counts are also tracked year over year to identify and compare trends.

NOTE: Our pollen collection process is heavily dependent on having good weather conditions for gathering the sample and at times, we are unable to provide accurate data. In these cases, please refer to the seasonal year-over-year data we provide, as it is generally a good indicator of current conditions.