WHY THE SUDDEN OUTBREAK, AND HOW CAN I AVOID IT?

A reduced use of home pesticides may have led to a comeback, says Jen House of the Ohio Department of Health. Another theory: "Our society is mobile: Bedbugs are coming with us," says Missy Henriksen of the National Pest Management Association. To avoid bringing home unwanted souvenirs, "check your hotel room. When you return, wash your clothing in hot water, dry it on a hot cycle and vacuum your suitcase." You can check the user-generated bedbugregistry.com for hotels and apartments with outbreaks.

HOW DO I KNOW IF I HAVE THEM?

Adults are brown and the size of a lentil; babies are yellow and even smaller. To spot them, "look behind the headboard and in the mattress seams for little brown things moving or droplets that stain the sheets," says Gary Alpert, a Harvard entomologist.

WHAT DO BITES LOOK LIKE?

Louis Sorkin, an entomologist at the American Museum of Natural History in New York City, says they can show up as red welts or be invisible. "They don't have to be in clusters." He adds that bites can take up to two weeks to appear.

I HAVE BEDBUGS. HELP!

Put clothes and linens in a dryer on high heat; the bugs can't survive temperatures over 113 degree Fahrenheit. To debug your bed frame, call a professional who can kill bugs hiding deep in crevices, says Alpert. (Do not use pesticides meant for outdoor use, which can be poisonous.) Also, a plastic casing on your mattress can suffocate bugs.

WILL I GET SICK?

"Bed bugs don't transmit diseases," says Henriksen. "But they can cause anxiety. This is not a pest to be embarrassed about: It doesn't mean your home is dirty. It can affect everybody."