Main source of airborne pollen varies by month

People with seasonal allergies know that some months can be tougher than others. An unprecedented 15-year study conducted in the New York City area charts how air concentrations of different types of pollen vary throughout an average year.

PUBLIC ENEMY #1. This common allergen, ragweed pollen, is shown dispersed on a ragweed plant in this scanning electron micrograph. CDC/J. Carr

Ragweed pollen, the most significant cause of allergy, is airborne mainly during August and September, report researchers at the University of Medicine and Dentistry of New Jersey–New Jersey Medical School in Newark.

By contrast, tree pollen is most abundant during May and is nearly absent from the air after the end of June. Grass-pollen concentrations peak in June and rise again, albeit to a lesser extent, in September.

Contrary to what some people with allergies might think, pollen abundance has decreased—at least in the New York City area—over the past decade.

The new data might help some people avoid unnecessary outdoor exposure at times when their allergies are most likely to be active, Leonard Bielory and his colleagues say in the May Annals of Allergy, Asthma and Immunology. They note that seasonal pollen patterns are likely to differ from one region of the country to the next.

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