The common bed bug, Cimex lectularius, is a small, nocturnal parasite that feeds exclusively on the blood of warm-blooded hosts, primarily humans. While the presence of bed bugs is a legitimate concern, understanding their biology can alleviate fears about internal infestations. Their physical structure and established behavior patterns make internal infestation of humans biologically impossible.
Bed Bug Size and Behavior
An adult bed bug is approximately the size and shape of an apple seed, measuring about 5 to 7 millimeters in length, and has a broadly oval, flattened body. This size immediately prevents entry into small human orifices such as the nose or ear canal. Even a newly hatched nymph, though much smaller, is still too large to navigate the narrow passages of the human body.
The bed bug’s extremely flat shape is an adaptation for hiding in narrow cracks and crevices, often the width of a credit card, near a sleeping host. Their behavior is strictly external; they are designed to move across surfaces to locate a host, not to burrow or live internally. Bed bugs are not equipped for the internal environment, which lacks the necessary external surfaces for movement and access to their food source.
How Bed Bugs Interact with Humans
Bed bugs are attracted to humans primarily by the carbon dioxide we exhale and our body heat. Their feeding activity typically peaks between midnight and 5:00 AM, coinciding with the deepest period of human sleep. This is a stealthy, external interaction where the pest briefly visits the host to feed and then retreats.
The insect pierces the skin using a specialized, elongated mouthpart called a proboscis. During the bite, the bed bug injects saliva containing an anesthetic to prevent the host from waking, along with an anticoagulant to keep the blood flowing. The bug remains on the skin’s surface for only about three to ten minutes to become engorged with blood before quickly returning to its hiding spot.
Actual Health Concerns from Infestations
The true health risks associated with a bed bug infestation are related to external and psychological effects. The most common physical reaction is a localized allergic response to the injected saliva, which results in itchy, red welts on the skin. The intensity of this reaction varies widely, and some people may show no visible reaction at all.
Excessive scratching of the irritating welts can break the skin barrier, creating an opening for bacteria to enter, which may lead to secondary skin infections like impetigo or cellulitis. Beyond the physical symptoms, the psychological toll of an infestation is often the most debilitating consequence, manifesting as significant anxiety, insomnia, and sleep deprivation. In extremely rare cases of severe, chronic infestation, blood loss has been linked to anemia, particularly in vulnerable populations.