What Is a Pollen Count?

For people who suffer from hay fever and certain other allergies, it’s important to know how much pollen is in the air. Some people who are very sensitive to pollen go away during peak pollen seasons, and they want to know what the pollen count is before they return home.

A pollen count is, quite simply, a count of pollen grains. To take a pollen count, scientists put a glass slide in the open air, and coat one side of the slide with an oil. The pollen grains, which float freely through the air, land on the slide and stick to the oil.

After about 24 hours, the scientists can count the number of pollen grains on the slide by looking at it under a microscope. They then issue a “pollen count,” which shows relatively how much pollen is in the air that day.

Many factors influence the pollen count. Heavy rains and strong sun lead to more pollen, while very dry or humid weather can reduce it.

A single plant may release more than 100,000 grains of pollen!