The Allergy Capitals is an annual research project of the Asthma and Allergy Foundation of America (AAFA). In the spring and fall it indentifies "the 100 most challenging places to live with allergies." The rankings are based on scientific analysis of 3 factors for the 100 largest metro areas in the U.S. The data measured and compared each year includes:
Pollen scores (airborne grass/tree/weed pollen and mold spores)
Number of allergy medications used per patient
Number of allergy specialists per patient
Here are the top five Fall 2010 Allergy Capitals according to the study. You can see the full list of 100 here (PDF).