Bed bugs usually bite people at night while they are sleeping. Hungry bed bugs may also feed during the daytime, especially if this is when the occupant normally sleeps. They feed by piercing the skin with an elongated beak through which they withdraw blood. Engorgement of the bed bug takes roughly three to 10 minutes, but because the bite is painless, the person seldom realizes they are being bitten. Bed bugs normally do not reside on people like head or body lice do; instead, immediately after feeding, bed bugs crawl to a secluded location to digest their meal. Symptoms after being bitten by bed bugs vary from person to person. Many develop an itchy red welt within a day or so of the bite. Others have little or no reaction. Sometimes the reaction is delayed days or even weeks after the actual bite occurs, which can make it difficult to determine where or when bites actually occurred. Studies conducted in bed bug-infested apartments suggest about 30 percent of people do not react even when bitten repeatedly over time, and there is still higher incidence of non-reactivity among the elderly. Unlike flea bites, which occur mainly around the lower legs and ankles, bed bugs feed on any skin exposed while sleeping (face, neck, shoulders, back, arms, legs, etc.). The welts and itching are often wrongly attributed to other causes, such as mosquitoes. For these reasons, infestations may go a long time unnoticed, and can become quite large before being detected. 
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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