Merck Manual

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Bedbug Infestation


James G. H. Dinulos

, MD, Geisel School of Medicine at Dartmouth

Last full review/revision Jun 2020| Content last modified Jun 2020
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Bedbugs are tiny, wingless insects whose bites are usually painless but can cause itchy skin reactions.

Parasites are organisms that live on or inside another organism (the host) and depend on the host for nutrition to live. Bedbugs are parasites because they live by sucking the blood of humans and some other animals. The most common bedbugs affecting humans are Cimex lectularis (in climates that are mild or moderate in temperature) and Cimex hemipterus (mainly in climates that are tropical). Bedbugs are reddish brown in color and have no wings. They range in size from 1/25 to more than a 1/4 inch (1 to 7 millimeters). They can live for several months without feeding on blood.

Bedbug infestations have become more common in the developed world in recent years. Bedbugs are flat and hide in the cracks and crevices of mattresses and in other structures such as bed frames, cushions, and walls. People may see bedbug feces or blood on bed linens or behind wallpaper. In undeveloped regions, they hide in structures such as mud houses and thatched roofs.

Bedbugs move slowly. They are attracted from their hiding places by the body heat and carbon dioxide that people produce. They bite any area of exposed skin, usually when people are sleeping. Before feeding, bedbugs are flat and reddish brown. After a blood meal, they are less flat and more red. A feeding is completed in 5 to 10 minutes, after which the bedbugs return to their hiding places.


Bite marks appear on the skin sometime between a few hours to 10 days after being bitten. They may look like any of the following:

  • Tiny holes only

  • Purplish flat spots

  • Red spots, solid raised bumps, or hives (wheals) that are often itchy and have a tiny hole in the center

  • Blisters

The bites are painless but can become itchy in some people. They may appear in line-like patterns or may be seen in clusters. Older adults develop symptoms less often than younger people. The bite marks go away after about 1 week. If people scratch the bites, they may develop an infection.

People may be anxious about the difficulty and expense of getting rid of a bedbug infestation. They may also experience emotional distress because they may no longer be invited to others' homes or may be shunned by family and friends, or they may isolate themselves to avoid spreading the bugs.


  • A doctor's evaluation

Doctors base the diagnosis on the appearance of the bite marks, but diagnosis may be difficult because the appearance can vary. However, most bedbug bites are larger than other bites (such as flea bites).

To confirm the diagnosis, doctors may try to identify the bedbug.


  • Treatment of symptoms

Doctors give creams that contain corticosteroids, antihistamines taken by mouth, or both to relieve the itching and other symptoms caused by the bites.

Bedbugs should be exterminated using physical and, usually, chemical methods. Physical methods include vacuuming infested areas and washing articles of clothing or bed linens, then drying them on the dryer's hottest setting. In addition, entire rooms should be treated by professional exterminators when possible. Professionals may heat the room to a temperature above or equal to 122° F (50° C) or may use multiple insecticides.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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