Allergists also say the results highlighted in the report cannot accurately predict whether there really is an increase in the amount of ragweed or mold in the air.
"A rising trend in ragweed allergies is entirely different from a rise in ragweed allergen," said Dr. Harold Nelson, a senior staff physician at National Jewish Hospital in Denver. "One is related to air sampling for pollen and one to [antibody] sensitization of patients, usually ascertained by skin testing."
Ragweed is most common along the East Coast and in the Midwest. Ragweed and other pollens have been present in record amounts in certain parts of the country because of the unusually heavy rainfall.
"Winter and spring precipitation have created a 'perfect storm' for heavy pollen levels and molds," said Dr. Clifford Bassett, medical director of Allergy and Asthma Care of New York. "Higher pollen levels [have] in part [been] from increased carbon dioxide (greenhouse gases) that supercharge plants, trees, etc. to produce and release more pollen."
Experts also say ragweed seasons are getting longer, especially in the Southwest, where it can plague allergy sufferers well into the fall.
Whether ragweed levels are truly higher and whatever may be causing them, it's going to be a very long summer -- and possibly fall -- for millions of Americans.
"The allergic epidemic is here to stay," said Bassett.