Allergens are widespread, but highly variable in U.S. homes, according to the nation’s largest indoor allergen study to date. NIEHS researchers reported that more than 90 percent of homes had three or more detectable allergens, and 73 percent had at least one allergen at elevated levels. The findings were published Nov. 30 in the Journal of Allergy and Clinical Immunology.
Shedding light on contributors to asthma and allergy
“Elevated allergen levels can worsen symptoms in people who suffer from asthma and allergies, so it is crucial to understand the factors that contribute,” said NIEHS Scientific Director Darryl Zeldin, M.D., the paper’s senior author.
Using data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES), the researchers studied levels of eight common allergens — cat, dog, cockroach, mouse, rat, mold, and two types of dust mite allergens. The team analyzed data from the bedrooms of nearly 7,000 U.S. homes.
They found that the presence of pets and pests had a major influence on high levels of indoor allergens. Housing characteristics also mattered — elevated exposure to multiple allergens was more likely in mobile homes, older homes, rental homes, and homes in rural areas.
For individual allergens, exposure levels varied greatly with age, sex, race, ethnicity, and socioeconomic status. Differences were also found between geographic locations and climatic conditions. For example, elevated dust mite allergen levels were more common in the South and Northeast, and in regions with a humid climate. Levels of cat and dust mite allergens were also found to be higher in rural areas than in urban settings.
Patterns of exposure and sensitization differ
To provide a more complete picture, the research team also compared allergen exposure and previously reported sensitization patterns from this survey. Sensitization, which makes a person’s immune system overreactive to allergens, may increase the risk of developing allergies and asthma. NHANES 2005-2006 allowed national level comparisons of exposure and sensitization for the first time.
The team uncovered several differences. Males and non-Hispanic blacks were less likely to be exposed to multiple allergens. Yet, sensitization was more common in these groups compared to females and other racial groups, respectively. Patterns also differed for urban and rural settings. Exposure to several elevated allergens was most prevalent in rural areas, whereas sensitization rates were shown to be higher in urbanized areas.
Overlaps were also found. Exposure and sensitization were both most prevalent for dust mite allergens in the South and Northeast, and for cockroach allergen in the South. Patterns also reflected socioeconomic variations, especially for pet and cockroach allergens, according to lead author Paivi Salo, Ph.D., of NIEHS.
The researchers emphasized that the relationships between allergen exposures, allergic sensitization, and disease are complex. Scientists continue to research how allergen exposures interact with other environmental and genetic factors that contribute to asthma and allergies.
“Asthma and allergies affect millions of Americans,” Salo said. “We hope this comprehensive study provides beneficial information to a wide audience, from patients to clinicians.”
Salo PM, Wilkerson J, Rose KM, Cohn RD, Calatroni A, Mitchell HE, Sever ML, Gergen PJ, Thorne PS, Zeldin DC. 2017. Bedroom allergen exposures in U.S. households. J Allergy Clin Immunol; doi:10.1016/j.jaci.2017.08.033 [Online 23 November 2017].
Salo PM, Arbes SJ Jr, Jaramillo R, Calatroni A, Weir CH, Sever ML, Hoppin JA, Rose KM, Liu AH, Gergen PJ, Mitchell HE, Zeldin DC. 2014. Prevalence of allergic sensitization in the United States: results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006. J Allergy Clin Immunol 134(2):350–359.
(Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison and a regular contributor to the Environmental Factor.)