Typically the first sign of a bed bug infestation starts with small, painless bites on your body. The salivary fluid injected by bed bugs typically causes the skin to become irritated and inflamed, although individuals can differ in their sensitivity. A small, hard, swollen, white welt may develop at the site of each bite. This is accompanied by severe itching that lasts for several hours to days.

Bedbugs are obligatory hematophagous (bloodsucking) insects. Most species feed on humans only when other prey are unavailable. Bedbugs are attracted to their hosts primarily by carbon dioxide, secondarily by warmth, and also by certain chemicals. A bedbug pierces the skin of its host with two hollow feeding tubes. With one tube it injects its saliva, while with the other it withdraws the blood of its host. After feeding for about five minutes, the bug returns to its hiding place.

Adult bedbugs are reddish-brown, flattened, oval, and wingless. Bedbugs have microscopic hairs that give them a banded appearance. Adults grow to 4–5 mm in length and 1.5–3 mm wide. Newly hatched nymphs are translucent, lighter in color and become browner as they moult and reach maturity. The life span of bedbugs varies by species and is also dependent on feeding.