Bed bug bites are caused primarily by two species of insects: Cimex lectularius (the common bed bug) and Cimex hemipterus.[3] They are about 1 to 7 mm in size.[7] Spread is by the bugs walking between nearby locations or being carried within personal items.[2] Infestation is rarely due to a lack of hygiene but is more common in high density areas.[8][2] Diagnosis involves both finding the bugs and the occurrence of compatible symptoms.[5] Bed bugs spend much of their time in dark locations like mattress seams or cracks in the wall.[2]

Most bites will have a small clear area in the center surrounded by redness that may or may not be raised. People tend to become more sensitive and have larger reactions after each episode. Reactions can include itch, swelling, rash and wheals (large round red area on the skin). Severe reactions can cause skin blisters and trouble breathing, although these reactions are very rare. 
They also have the ability to travel beyond the bedroom, so all adjoining rooms should be checked for infestation. Any area that offers a layer of protection, e.g. dark, isolated areas, should be checked. They do leave excrement droppings behind, so even if they are not seen, you can often see where they have been. The best method to find them is to check only at night, and with a red light.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Bedbugs bite and suck blood from humans. Bedbugs are most active at night and bite any exposed areas of skin while an individual is sleeping. The face, neck, hands, and arms are common sites for bedbug bites. The bite itself is painless and is not noticed. Small, flat, or raised bumps on the skin are the most common sign; redness, swelling, and itching commonly occur. If scratched, the bite areas can become infected. A peculiarity of bedbug bites is the tendency to find several bites lined up in a row. Infectious-disease specialists refer to this series of bites as the "breakfast, lunch, and dinner" sign, signifying the sequential feeding that occurs from site to site. In some people, the bites can take several days to develop. The signs may become apparent up to 14 days after the bite has occurred.
Unlike those of other insects, bed bug bites may sometimes appear in tight lines of multiple, small, red marks where multiple bed bugs have fed along an exposed area. Bed bug bites can cause itchiness. Initially, a victim may detect a slight burning sensation. The burning area then develops red bumps, known as papules or wheals (rash). In extreme cases, bites may swell dramatically or turn into blister-like skin inflammations.
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