Bed bugs bite humans in order to feed on their blood. They are nocturnal and usually only bite while their human hosts are sleeping. Because a bed bug bite is painless, it can be difficult to identify the cause of the bite. Many people experience reactions to a bed bug bite similar to that of a mosquito or flea bite and the most common symptoms include redness, itching and swelling. Bites are not dangerous, unless an allergic reaction to the bite occurs. If at any time you feel that the bite is serious, seek medical help as soon as possible.