To collect a sample of particulates in the air, a plastic rod or similar device is covered with a greasy substance. At the end of that time, a trained analyst studies the surface under a microscope. Pollen and mold that have collected on the surface are identified by size and shape as well as other characteristics. A formula is then used to calculate that day's particle count. The counts reported are always for a past time period and may not describe what is currently in the air.
Some counts reflect poorly collected samples and poor analytical skills.
They may not break out the particular pollen or mold that causes your allergies. This means that allergy symptoms may not relate closely to the published count. But knowing the count can help you decide when to stay indoors. Allergies cannot be cured. But the symptoms of the allergy can be reduced by avoiding contact with the allergen.