Bedbug Bites

Bed bugs (Cimex lectularius, and the tropical bed bug Cimex hemipterus in warmer climates) are small, wingless, nocturnal insects that feed on blood and hide in cracks and crevices near where people sleep, emerging at night to feed.^[1] They are not known to transmit any human disease — no study has demonstrated that a bed bug transmits a pathogen to a person outside laboratory conditions, and their bites do not generally require medical attention.^[1][2] What a pharmacist actually manages is the bite reaction itself: itchy, erythematous papules on exposed skin that most often appear within 24-48 hours of a bite but can take as long as 14 days, and that some people never visibly react to at all.^[3][1]

Bed bugs underwent a global resurgence beginning in the 1990s, driven by increased international travel together with insecticide resistance that is now close to universal in tested populations — genotyping of bed bug colonies collected in the United States found resistance gene variants in 100% of colonies sampled in 2018-2019, up from 97.5% a decade earlier.^[3][2][4] This chapter frames bed bug bites the way pharmacist practice should: the bites are a genuinely treatable dermatologic (and occasionally infectious or psychiatric) presentation, but the underlying infestation itself is a pest-control problem, not a pharmacotherapy problem. No oral or topical medication clears an infestation, and the pharmacist's central non-drug intervention is steering the patient toward genuinely effective physical and professional pest control and away from ineffective or unsafe self-treatment (foggers, homemade pesticides, unregistered products, ozone generators).^[5]

Adult Cimex lectularius feeding on human skin — the flat, oval, wingless, reddish-brown body typically measures 5-7 mm. (CDC Public Health Image Library #9820, public domain; content providers CDC/Harvard University — Dr. Gary Alpert, Dr. Harold Harlan, Richard Pollack; photo credit Piotr Naskrecki; via Wikimedia Commons)

Bite pathophysiology and the sensitization pattern

The bite reaction is an immunologic response to proteins in bed bug saliva — including nitrophorin (a vasodilator), apyrase (which inhibits platelet activation and aggregation), and a factor X inhibitor — injected through needle-like stylets during feeding.^[2] Reactions follow a pattern of progressive sensitization with repeated exposure: a previously unbitten person typically develops no visible reaction at all to the first bite, or a delayed papule appearing roughly 8-10 days later; with repeated exposure the latency shortens, eventually producing an immediate wheal-and-flare reaction within minutes, as the immune response shifts from a primary to a memory-mediated (secondary) response.^[2] This matters clinically because a patient in a newly infested home may not develop a visible lesion for more than a week, which can delay recognition.^[2]

What the bites actually look like

The classic lesion is an itchy, erythematous maculopapule, typically 2-5 mm, sometimes with a hemorrhagic punctum at the centre marking the stylet-insertion site.^[3][2][6] Less common presentations include wheals, linear lesions, bullae, and vesicles; large urticarial wheals exceeding 1 cm can occur, and more severe reactions — bullous eruptions or hypereosinophilia — have been reported, though uncommonly.^[3][2] Bites concentrate on skin left exposed overnight — face, neck, arms, and hands most often, though any uncovered area can be affected.^[3][1]

Bed bug bites roughly four days old, in a linear grouping along the outside of the forearm and wrist. (Oliver Arend, CC BY-SA 3.0, via Wikimedia Commons)

The "breakfast, lunch, dinner" sign — a real but overrated finding

A linear or clustered grouping of 3 or more bites — popularly the "breakfast, lunch, dinner" sign, attributed to a single bug repeatedly interrupting its feeding while moving along the skin in search of a larger vessel — is a classic teaching finding.^[2] It is genuinely useful when present, but should not be treated as required for diagnosis: a systematic review of published case reports found this hallmark pattern in fewer than half of confirmed cases, and similar grouped-bite patterns occur with other arthropod exposures, including fleas and kissing bugs.^[2]

Not everyone reacts — and not reacting does not rule out exposure

Roughly 20-30% of people bitten remain anergic and never develop a visible skin finding at all.^[2] Even among people who do react, a large U.S. infestation study found skin reactions in only about 70% of affected individuals overall, with meaningfully lower rates in adults over 65 (58%) and children aged 1-10 (59%).^[2] A normal skin examination in a household contact of a confirmed infestation therefore does not exclude exposure.

Resolution

Once biting actually stops — either because the patient has left the infested environment or because the infestation has been eradicated — lesions resolve within about 1-2 weeks without specific treatment.^[3][2] Bites that keep appearing past that window mean the infestation, not the treatment, has failed (see Treatment Failure / Next Step).

• Recent travel, especially hotel stays, and particularly hotels with high guest turnover.^[2]
• Residence in densely populated, multi-unit housing (apartment buildings, shelters, group homes) — infestations spread readily between units through structural conduits (power outlets, air ducts, shared walls) as well as by passive transport in used furniture, luggage, and bags.^[2]
• Lower socioeconomic status — a large 2017 Montreal Housing Survey of 5,000 tenants found bed bug exposure was socially patterned, disproportionately affecting people facing housing and economic vulnerability, with 4% of tenants reporting exposure in the preceding year.^[7]
• Recent acquisition of used furniture, mattresses, or clothing of unknown history.^[2]
• Residence in a group home or similarly congregate setting — a documented risk factor, and one with particular relevance to patients who also carry a psychiatric diagnosis (see Special Populations and the delusional-parasitosis discussion below).^[8]
• Bed bugs occur equally in both sexes and across all age groups — there is no demographic group that is inherently protected.^[2]
• Bed bugs cannot fly or jump; they hitch a ride on a person's belongings or move along structural conduits, so risk tracks with exposure to an already-infested environment or object rather than with any patient-specific biological susceptibility.^[1][3]

Diagnosis is clinical

There is no routine laboratory test for bed bug bites. Clinical suspicion rests on the bite appearance together with a compatible exposure history; definitive confirmation requires actually finding and identifying a bed bug specimen or other direct evidence of infestation.^[2] Specialized Western blot serology for bed bug salivary antigens has been described (for example, in returning international travellers with an unexplained eruption after a hotel stay) but is costly and available only through specialized laboratories — not a routine tool.^[2]

History

• Timing of new lesions relative to sleep/waking, since bites are acquired overnight.
• Recent travel, hotel stays, or stays in shared/congregate housing.
• Recent acquisition of used furniture, mattresses, or clothing.
• Whether other household members or roommates are also affected.
• Any evidence the patient has already seen: live insects, blood-spotting on sheets, small dark fecal spots on the mattress or bedding, or shed exoskeletons.^[2]

Environmental evidence

Visual inspection for fecal spotting (small dark deposits on mattress seams and bedding) and shed skins remains the most accessible detection method. Passive interceptor traps placed under bed legs detected 89% of infestations in a study of low-income apartments and are a reasonable low-cost tool to recommend; commercial canine scent-detection teams exist but have variable field accuracy (a mean detection rate of 44% in one evaluation), and carbon dioxide or heat-lure active monitoring devices are also available.^[2]

Differential diagnosis

Bed bug bites should be considered in any patient with an unexplained or undiagnosed pruritic eruption, but several other causes need to be actively distinguished — not simply assumed away.^[2]

Investigations

No routine bloodwork is needed for a typical presentation. A biopsy is rarely indicated and reserved for atypical or refractory lesions under dermatology; when performed, it shows edema with perivascular lymphocytic and eosinophilic infiltration.^[2] Consider a CBC only if an unusually severe reaction raises concern for hypereosinophilia.^[2]

• Relieve pruritus and discomfort so the patient can sleep and avoid the scratch-excoriate-infect cycle.
• Recognize and promptly treat secondary bacterial infection when it develops.
• Correctly triage the small subset of patients who need urgent escalation — anaphylaxis, spreading infection with systemic signs, or delusional parasitosis with risk features.
• Get the patient onto genuinely effective infestation control — physical control measures now, plus a licensed professional pest control operator — since the bites themselves cannot be "cured" by pharmacotherapy while the underlying infestation continues.
• Screen for and validate the real psychological impact of infestation, and refer for mental health support when it is significant.
• Actively steer patients away from ineffective or unsafe self-treatment: unregistered pesticides, homemade pesticide recipes, insect foggers/"bug bombs," and ozone generators.

Reduce excoriation and secondary infection risk

• Discourage scratching — keep nails short, use cool compresses, and treat pruritus adequately (see Choose Initial Treatment) specifically to break the scratch-excoriate-infect cycle.
• Keep bite sites clean; an antiseptic cream or lotion can help.^[1]

Physical control of the infestation — start now, regardless of whether a professional has been booked

• Vacuum daily using a stiff brush attachment and a nozzle for seams and crevices — mattress, box spring, bed frame, baseboards, furniture cushions, rugs, and inside/underneath drawers and furniture. Dispose of the vacuum bag (or bagless canister contents) in a sealed plastic bag immediately; wash attachments in hot water; a HEPA-filter vacuum is preferable, especially for household members with allergies or asthma.^[5]
• Steam-clean mattresses, upholstery, and other items that cannot be washed — bed bugs die at 50°C, and steam cleaners typically emit steam at 100°C or higher; move the steamer slowly to maximize depth of penetration, and avoid excess moisture that could promote mould.^[5]
• Wash bedding, mattress pads, curtains, and infested clothing in hot water and dry on the hottest dryer setting; place small non-washable or dry-clean-only items in a hot dryer for 30 minutes or more.^[5]
• Freezing small items can help, but freezing temperature must be maintained for a prolonged period (about 4 days at a consistent -19°C) and may not kill every bed bug — professional heat treatment (45-48°C for 1 hour, or direct steam at 60°C, which kills bed bugs in under a minute) and professional freezing protocols (-20°C for at least 2 hours) are more reliable and are generally left to trained operators.^[5][2]
• Store clean, dry items in light-coloured, sealed heavy-duty plastic bags or bins with secure lids to avoid re-infesting other areas, and discard any item that cannot be washed, heated, or steam-cleaned.^[5]

Hire a licensed professional pest control operator

Physical control alone is rarely sufficient — effective eradication needs a combination of chemical and mechanical methods together, and professionals have access to tools (liquid and aerosol insecticide sprays, insecticidal dusts, diatomaceous earth, pressurized carbon dioxide "snow," and steam/heat treatment) that are properly matched to a confirmed infestation.^[5][3] Contact information for exterminators can be found through the Canadian Pest Management Association or a provincial pest management association.^[5] Complete eradication commonly takes weeks to months and often needs more than one treatment visit.^[2]

Tenants

A tenant who discovers bed bugs should notify their landlord right away; if the landlord does not respond, a public health officer can help with the process.^[5] If a building management team has scheduled treatment, they will typically ask the tenant to empty storage furniture, bag belongings, wash all clothing and bedding, and move furniture away from the walls beforehand.^[5]

Preventing spread while travelling

• Inspect the hotel room, and specifically the mattress and headboard seams, before unpacking; if bed bugs are found, ask for a different room (not simply the adjoining one) or change hotels.^[3]
• Keep luggage elevated off the floor and bed, and away from upholstered furniture, where possible.^[3]
• When visiting a dwelling known or suspected to be infested: wear disposable shoe covers and clothing that can go straight into a hot dryer afterward, bring minimal belongings, hang bags and coats up high or keep them in sealed plastic containers, and bring a stool or sit only on hard chairs without cushions.^[3]
• On returning home, launder travel clothing in hot water and dry on the hottest setting, and inspect luggage carefully before bringing it back inside.^[2]
• Avoid acquiring used mattresses, upholstered furniture, or clothing of unknown history.^[2]

Reassurance and psychosocial support

• Reassure patients that bed bugs are not known to transmit disease — this alone can meaningfully reduce anxiety.^[1][2]
• Take the psychological burden seriously rather than minimizing it: anxiety, insomnia, social isolation, and stigma are common, well-documented consequences of infestation, not an overreaction.^[3][7]
• Older adults and people with disabilities often need practical, hands-on support to carry out eradication successfully — connect them with community or social work resources where cost or physical capacity is a barrier; the average cost of professional eradication for a single-family home is roughly $1,225, a real barrier for low-income patients.^[3][2]
• Caring for a patient with bed bug bites carries no meaningful skin-to-skin transmission risk — reluctance to examine or physically assess an affected patient is a misconception, not a genuine precaution.^[2]

Pregnancy

Preferred a non-sedating oral antihistamine (loratadine or cetirizine) and a low-potency topical corticosteroid (hydrocortisone) for pruritus; cephalexin is a reasonable choice if an oral antibiotic is needed for secondary infection. Tell the professional pest control operator that the patient is pregnant so an appropriate product and treatment timing can be chosen, and avoid unnecessary personal exposure to pesticide application. Do not use an ozone generator under any circumstances — Health Canada's warning applies regardless of pregnancy status, and the associated respiratory irritation is an added reason for caution.^[5]

Breastfeeding

Cetirizine, loratadine, low-potency topical corticosteroids, and cephalexin are all considered compatible with breastfeeding at standard doses; confirm specifics against each drug's own Drug Database entry. Sedating antihistamines (diphenhydramine, hydroxyzine) can reduce infant alertness/feeding if used regularly and are best reserved for occasional night-time use.

Pediatrics

Visible bite reactions are meaningfully less common in young children (about 59% in children aged 1-10, versus about 70% overall), so the absence of visible lesions does not rule out exposure in a child from an infested home.^[2] Use weight-based, age-appropriate dosing for antihistamines and confirm age restrictions on any OTC product before recommending it for a young child. Children's skin is more prone to excoriation and secondary infection from scratching — treat pruritus promptly and keep nails trimmed. Health Canada is explicit that pesticides must never be used on cribs, playpens, or toys, and never on people, pets, or bedding unless the specific product label says so.^[5]

Older adults

Older adults also show a lower visible reaction rate (about 58%), so maintain suspicion even without visible lesions in a confirmed-infestation setting.^[2] Use caution with anticholinergic sedating antihistamines (diphenhydramine, hydroxyzine) given fall and cognitive-impairment risk — prefer a non-sedating option where pruritus allows. Older adults, along with people with disabilities, often need genuine practical support (physical help with laundering, decluttering, and coordinating a professional visit) to carry out eradication successfully, and this population is disproportionately affected by the psychological toll of infestation.^[3]

People experiencing housing vulnerability, low income, or congregate/shared housing

Exposure to bed bugs is socially patterned: the 2017 Montreal Housing Survey found infestations more prevalent in high-density multi-unit housing and disproportionately affecting tenants facing broader housing and economic vulnerability.^[7] The average cost of professional eradication (roughly $1,225) is a genuine barrier for low-income patients, making social work and community-resource involvement a legitimate part of management, not an optional extra.^[2] Group home residents are a specifically documented higher-risk group and may also carry a higher burden of psychiatric comorbidity relevant to the delusional-parasitosis discussion below.^[8]

Patients with a psychiatric history, or where delusional parasitosis is a concern

A real bed bug infestation can precipitate or worsen delusional parasitosis in a vulnerable patient, particularly with an underlying psychiatric condition such as schizophrenia, bipolar or schizoaffective disorder, or a history of substance use.^[9][8] The essential rule is sequencing: genuinely rule out an actual, ongoing infestation first, with real evidence (inspection findings, a captured specimen, corroboration from a professional pest control operator) — do not assume a patient's continued complaints are delusional simply because a previous treatment "should" have worked, since infestations do fail to clear and can be reintroduced.^[9] Once true parasitosis is genuinely excluded, involve psychiatry for a fixed false belief, a "matchbox sign" presentation, or self-harm/risk behaviours (e.g., using unsafe substances on the skin or belongings, or fire-setting) in response to the belief.^[8]

• Set an explicit expectation at the first visit: bites should stop appearing and existing lesions should resolve within about 1-2 weeks once the infestation is actually controlled — new bites past that window mean the infestation, not the treatment, needs attention.^[3][2]
• Follow up specifically on whether professional pest control was actually arranged, not only on symptom relief — eradication commonly takes weeks to months and often needs more than one treatment visit, and patients may quietly abandon the process due to cost or logistics.^[2]
• Watch for signs of secondary infection developing after the initial visit (increasing redness, warmth, swelling, pain, spreading, or fever) and escalate promptly if they appear.
• For a topical corticosteroid, confirm short-term use only and taper/discontinue once lesions have resolved rather than continuing indefinitely.
• Reassess psychological symptoms (anxiety, sleep disturbance, mood) at follow-up given the documented association between bed bug exposure and both anxiety and depression, and refer for mental health support if symptoms are significant or persistent.^[7]
• For a tenant, confirm whether the landlord was notified and whether the situation has actually progressed — offer information on contacting a public health officer if it has stalled.^[5]

1. New bites continuing to appear beyond about 2-3 weeks despite self-care: this means the infestation itself is not controlled, not that the antipruritic regimen has failed — reassess whether physical control measures were actually completed and whether a licensed professional has been engaged.
2. Pruritus not controlled by an OTC oral antihistamine plus a low-potency topical corticosteroid: step up to a moderate-potency prescription topical corticosteroid (confirming no infection first), and refer for consideration of an adjunct oral gabapentinoid if pruritus remains refractory.
3. Suspected secondary infection not improving within 48-72 hours of topical mupirocin or an oral antibiotic, or any new systemic symptom (fever, spreading erythema, lymphangitic streaking): escalate for prompt reassessment — consider antibiotic resistance, an incorrect original diagnosis, or the need for more aggressive therapy.
4. Recurrent bites in a home or unit after a professional treatment: eradication may not have been complete (given how widespread insecticide resistance now is), or reintroduction may have occurred through visitors, shared laundry facilities, or an adjoining unit — arrange repeat inspection and treatment, and, in a multi-unit dwelling, raise whether the issue is building-wide rather than unit-specific.
5. A patient who continues to report being bitten after confirmed, verified eradication, with no specimen or other objective evidence found: consider delusional parasitosis, but only after genuinely re-examining for a real, persistent, or reintroduced infestation — never dismiss the complaint outright, and involve a prescriber/psychiatry once true parasitosis is actually excluded.
6. Persistent anxiety, insomnia, or low mood despite the infestation itself being resolved: refer for dedicated mental health assessment rather than assuming symptoms will resolve on their own once the bites stop.

• Assuming a normal skin exam rules out bed bug exposure — up to 20-30% of people never develop a visible reaction at all, and reaction rates are lower still in older adults and young children.^[2]
• Over-relying on the "breakfast, lunch, dinner" linear/clustered pattern as if it were required for diagnosis — it is present in fewer than half of confirmed cases and can occur with other arthropod bites too.^[2]
• Treating bed bug bites as a purely dermatologic problem without addressing the underlying infestation — bites will keep recurring for as long as the infestation itself continues, regardless of how well the skin symptoms are managed.^[3][2]
• Recommending or condoning insect foggers/"bug bombs," homemade pesticide recipes, or any pest control product without a Health Canada PCP registration number — these are ineffective, unsafe, or both, and unregistered products are illegal to sell or use in Canada.^[5]
• Failing to specifically warn against ozone generators marketed for bed bug or mould control — Health Canada has issued a direct consumer warning that these devices are unsafe, unapproved for this use, and can cause real respiratory harm.^[5]
• Applying a moderate- or high-potency topical corticosteroid to excoriated or possibly infected skin without checking for infection first.^[2]
• Dismissing a patient's continued complaints of "still being bitten" after a documented professional treatment as simply anxious or delusional, without first genuinely re-examining for a persistent or reintroduced infestation — true parasitosis must always be excluded before delusional parasitosis is considered.^[9][8]
• Being reluctant to examine or physically assess a patient with suspected bed bug bites out of a misplaced concern about skin-to-skin transmission — meaningful transmission requires physical relocation of bugs from a harborage, not casual contact.^[2]
• Minimizing the psychological impact of an infestation as a trivial concern rather than a well-documented, measurable consequence that can warrant its own referral.^[7][3]
• Overlooking the rare but real possibility of anaphylaxis or a spreading secondary infection because "it's just bug bites."^[2]

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Oral Antihistamines for Pruritus

Non-sedating agents are preferred for daytime use; reserve a sedating agent for night-time itch that is disrupting sleep.

Topical Antipruritics and Corticosteroids

Confirm the skin is not already infected before applying a topical corticosteroid.

Secondary Bacterial Infection

Reserve for impetiginization, cellulitis, folliculitis, or lymphangitis arising from excoriation of the bite site; refer promptly if infection is spreading or systemic signs appear.

Anaphylaxis (rare)

True IgE-mediated bed bug allergy exists and anaphylaxis has been reported, though it remains exceedingly rare — treat exactly as any other insect-bite anaphylaxis.

Refractory Pruritus — Physician-Directed Adjunct

Not a pharmacist-initiated therapy; refer if pruritus remains refractory to an adequate trial of an oral antihistamine plus a topical corticosteroid.