Bed bugs leave large circles of bites in orderly rows. The bites cause itching, skin redness, localized swelling, as well as blisters regarding the bites. These spots eventually turn to small red bumps and fade after several days. The bites are not dangerous, though infections might result from scratching the bites.

Bed bugs are obligatory bloodsuckers. They usually have mouth parts that saw through the skin, and inject saliva with anticoagulants and painkillers. Sensitivity of humans varies from extreme allergic reaction to no reaction at all (about 20%). The bite usually produces a swelling without any red spot, but when many bugs feast upon a small area, reddish spots may appear following the swelling subsides. Bedbugs prefer exposed skin, preferably the face area, neck, and arms of a sleeping person.