SUNDAY, March 20 (HealthDay News) -- People with hay fever need to know that Web site pollen forecasts may not be all that reliable, researchers say.

The investigators looked at two popular Web sites that use predicted pollen forecasts and compared the results with pollen counts from the American Academy of Allergy, Asthma & Immunology's National Allergy Bureau (NAB). The NAB features a network of pollen counting stations staffed by volunteers who use air sampling equipment and microscopes to determine daily pollen levels.

Pollen levels, top three pollen lists, total counts and indices for the 2007 and 2009 pollen seasons from 12 NAB stations in the United States and one in Canada were compared to corresponding daily reports from the pollen count Web sites.

The researchers found that the predicted pollen information from the Web sites was different from the actual counts from the NAB stations.

"Predicted counts reported on many Web sites may be based on pollen data from previous years and general weather forecasts," Estelle Levetin, chair of the committee that oversees the NAB, said in an academy news release. "Pollen counts from the NAB stations are based on actual counts, which reflect the real day-to-day weather events."

The study was to be presented Sunday at the annual meeting of the American Academy of Allergy, Asthma & Immunology, held in San Francisco.

Experts note that research presented at meetings has not been subjected to the same type of rigorous scrutiny given to research published in peer-reviewed medical journals.

More information

The U.S. National Institute of Environmental Health Sciences has more about pollen.