Bed bugs are parasitic insects in the genus Cimex that feed exclusively on blood.

Cimex lectularius, the common bed bug, is the best known as it prefers to feed on human blood;

A bed bug can individually and collectively cause a number of health effects including skin rashes, psychological effects and allergic symptoms.

Individual responses to bites vary, ranging from no visible effect (in about 20–70%), to small macular spots, to prominent wheals and bullae formations along with intense itching that may last several days

Serious infestations and chronic attacks can cause anxiety, stress, and insomnia. Development of refractory delusional parasitosis is possible, as a person develops an overwhelming obsession with bed bugs.

Bed bugs classically form a line of bites colloquially referred to as "breakfast, lunch, and dinner" and rarely feed in the armpit or behind the knee which may help differentiate it from other biting insects.