A person can develop an allergic reaction to the common bed bug, Cimex lectularius. The typical reaction is a localized, itchy welt that appears hours or even days after the bite, which is a form of delayed hypersensitivity. A true, immediate allergic response is also possible, though it is far less common. The body’s immune system recognizes substances introduced by the insect as foreign invaders, triggering a defensive cascade.
The Source of the Immune Response
The primary triggers for human immune responses are proteins in the bed bug’s saliva, which are injected during feeding. Bed bugs are hematophagous, meaning they feed on blood, and their saliva contains compounds like anticoagulants and vasodilators to facilitate blood flow. These compounds, which can include various proteins, are identified by the host body as antigens.
The most common reaction is a Type IV delayed hypersensitivity response, where symptoms like localized red, itchy bumps develop slowly over 24 hours or more. Conversely, a true immediate allergy is a Type I hypersensitivity reaction, mediated by the antibody Immunoglobulin E (IgE), which can manifest rapidly. Beyond the bite itself, bed bug feces, shed skins, and dead bodies contribute to the overall allergen load. These contain high concentrations of histamine that can be inhaled, potentially causing respiratory symptoms.
Identifying Severe Reactions
The initial, localized reaction usually presents as pruritic, maculopapular lesions, which are small, raised, itchy spots. A severe or systemic allergic reaction extends beyond the immediate bite sites and requires immediate attention. These reactions can include large urticarial lesions, commonly known as hives, which appear as raised patches of skin.
More serious systemic symptoms involve generalized swelling, termed angioedema, which may affect the face, lips, or throat. Respiratory distress, such as wheezing or chest tightness, indicates a widespread allergic response affecting the airways. In rare instances, a person may experience anaphylaxis, a life-threatening systemic reaction involving a rapid drop in blood pressure and circulatory collapse.
Treating Allergic Symptoms
Management for mild reactions involves over-the-counter treatments to alleviate itching and inflammation. Oral antihistamines block the histamine response that causes itching and swelling. Topical anti-itch creams, such as calamine lotion or low-dose hydrocortisone, can be applied directly to the bite sites. Avoiding scratching the bites is important, as this can break the skin barrier and lead to secondary bacterial infections.
For severe, systemic reactions, professional medical attention is necessary to prevent complications. A healthcare provider may prescribe oral corticosteroids to manage widespread inflammation or stronger topical steroids. In the rare event of anaphylaxis, emergency measures, including the use of an Epinephrine auto-injector followed by prompt transport to an emergency room, are required. Eliminating the source of the exposure is the foundational step to prevent sensitization and further reactions.