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Bed bug-infested homes tend to be dusted with a layer of histamine particles, leading researchers to speculate that environmental histamine may be an indoor allergen with adverse health effects.

Inside infested homes, histamine levels averaged versus less than 2.5 μg/100 mg in control homes in the same apartment building (and less than 0.3 μg/100 mg in an uninfested building more than 8 km away), according Zachary DeVries, PhD, of North Carolina State University in Raleigh, and colleagues.

"Notably, the histamine concentrations in dust collected in bed bug-infested homes were 50-times greater than in agricultural hay," the authors wrote in PLOS One. "The high concentrations, persistence, and proximity to humans during sleep suggest that bed bug-produced histamine may represent an emergent contaminant and pose a serious health risk in the indoor environment."

"Histamine is used in bronchial and dermal provocation, but it is rarely considered an environmental risk factor in allergic disease," they noted.

The authors also reported that 3 months after bug elimination through heat treatment, histamine levels remained elevated in once-infested homes.

"Prolonged exposure of homes to temperatures of 50˚C [122˚F] did not reduce histamine levels in house dust. Therefore, a combination of deep cleaning and pest elimination will likely be needed, similar to the strategies used to reduce German cockroach allergens," DeVries' group suggested. "Unfortunately, there is no information on the health effects of chronic low-level exposure to histamine because prior to our study there was no compelling need for such an assessment."

They collected dust after surveying residences in a nine-story apartment building with 140 apartments. This was a building that had been chronically infested for several years despite attempts at pest control.

DeVries' group wound up with a sampling of Raleigh apartments that consisted of infested homes (n=14), uninfested homes within the same complex (n=10), and uninfested residences that had no evidence of bed bugs in at least 3 years and were located more than 8 km (about 5 miles) away (n=5).

"Low, but detectable, levels of histamine in some uninfested apartments within the same building suggest either that bed bugs had been present in these apartments at some prior time, or that some bed bugs were present but we failed to detect them," the researchers stated.

"Importantly, the high concentrations of histamine we recovered were from sieved dust particles which readily become airborne and represent the major route of entry of allergens into the airway, as documented in studies correlating cockroach allergens in settled and airborne dust. The potential health risks associated with bed bug-produced histamine might rival those associated with other indoor pests, namely cockroaches and dust mites," they noted. "Although unknown, we speculate that environmental histamine may have additive or synergistic interactions with other allergens."

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