From the NIH:  link to full article: http://t.co/QuVzGFPTDb

An excerpt (highlighted for emphasis):

In the largest, most comprehensive, nationwide study to  examine the prevalence of allergies from early childhood to old age, scientists  from the National Institutes of Health report that allergy prevalence is the  same across different regions of the United States, except in children 5 years  and younger.

“Before this study, if you would have asked 10 allergy  specialists if allergy prevalence varied depending on where people live, all 10 of them would have said yes, because allergen  exposures tend to be more common in certain regions of the U.S.,” said Darryl  Zeldin, M.D., scientific director of the National Institute of Environmental  Health Sciences (NIEHS), part of NIH. “This study suggests that people prone to  developing allergies are going to develop an allergy to whatever is in their  environment. It’s what people become allergic to that differs.”

The research appeared online in February in the Journal of  Allergy and Clinical Immunology, and is the result of analyses performed on  blood serum data compiled from approximately 10,000 Americans in the National  Health and Nutrition Examination Survey (NHANES) 2005-2006.

… Among children  aged 1-5, those from the southern U.S. displayed a higher prevalence of  allergies than their peers living in other U.S. regions. ..

“The higher allergy prevalence among the youngest children  in southern states seemed to be attributable to dust mites and cockroaches,”  explained Paivi Salo, Ph.D., an epidemiologist in Zeldin’s research group and  lead author on the paper. “As children get older, both indoor and outdoor  allergies become more common, and the difference in the overall prevalence of  allergies fades away.”

The NHANES 2005-2006 not only tested a greater number of  allergens across a wider age range than prior NHANES studies, but also provided  quantitative information on the extent of allergic sensitization. The survey  analyzed serum for nine different antibodies in children aged 1-5, and nineteen  different antibodies in subjects 6 years and older. Previous NHANES studies used skin prick tests to test for allergies.

The scientists determined risk factors that made a person  more likely to be allergic. The study found that in the 6 years and older  group, males, non-Hispanic blacks, and those who avoided pets had an increased  chance of having allergen-specific IgE antibodies, the common hallmark of  allergies.

Socioeconomic status (SES) did not predict allergies, but  people in higher SES groups were more commonly allergic to dogs and cats,  whereas those in lower SES groups were more commonly allergic to shrimp and  cockroaches.