In a study published in September in the Journal of Medical Entomology, researchers have found that, in a hypothetical infestation of 1,000 bed bugs (Cimex lectularius), they could produce up to 40 milligrams of histamine in a week. Excess histamine exposure can cause health effects ranging from rashes to headaches to respiratory problems. (Photo by Matt Barton, University of Kentucky College of Agriculture, Food and Environment)