Insect bites and stings
Exam Tips
- In UK exams, distinguish large local sting reaction from cellulitis: allergic swelling often peaks at 24-48 hours then improves, whereas cellulitis tends to progressively worsen with systemic upset.
- A sting in mouth/throat/tongue is an airway emergency even before overt obstruction develops.
- Do not miss anaphylaxis markers: rapid onset urticaria/angio-oedema plus airway, breathing, or circulation compromise after sting exposure.
- Tick bite OSCE point: remove promptly and document Lyme red flags (erythema migrans, fever, arthralgia, neuropathic symptoms).
- Bed bug clue: grouped/linear pruritic lesions on exposed skin in co-sleepers or recent travellers (see figure of typical linear bite pattern in dermatology teaching atlases).
- Wasp venom allergy is more common than bee venom allergy in the UK; prior systemic reaction warrants specialist allergy referral.
Definition
Insect bites and stings are cutaneous and sometimes systemic reactions that follow exposure to salivary proteins (bites) or injected venom (stings) from arthropods, including insects and arachnids. Most presentations are self-limiting local inflammation, but a minority progress to large local reactions, secondary infection, toxic effects after multiple stings, or life-threatening anaphylaxis.
Pathophysiology
Bites typically involve salivary anticoagulant/vasodilator proteins that trigger immune responses after sensitization. Delayed type IV hypersensitivity often appears 8-72 hours after repeat exposure as pruritic inflamed papules; with further exposure, immediate type I hypersensitivity can occur within minutes (wheal-and-flare), and rarely anaphylaxis. Stings (especially bee/wasp/hornet) inject venom containing allergenic enzymes (for example hyaluronidase, acid phosphatase) and vasoactive mediators (including histamine), producing pain, erythema, oedema, and in susceptible people systemic mast-cell-mediated reactions. Repeated exposure may eventually lead to partial desensitization in some individuals.
Risk Factors
- Outdoor exposure (gardening, hiking, camping, picnics), especially in summer
- Occupational exposure (beekeeping, forestry, outdoor manual work)
- Walking barefoot outdoors (increased risk of foot stings, especially bees)
- Domestic pets (higher risk of flea infestation)
- Atopy/atopic dermatitis (associated with papular urticaria in children)
- Previous systemic reaction to the same venom or bite source
- Travel to tropical/subtropical regions (unusual vectors and imported infections)
Clinical Features
Symptoms
- Local pain, itch, warmth, swelling, and erythema at bite/sting site
- Immediate painful sting (common with bee/wasp/hornet); some bites noticed later
- Large local reaction: marked itch/swelling spreading over >10 cm, peaking 24-48 hours
- Systemic allergy symptoms: generalized urticaria, flushing, rhinitis, wheeze, throat tightness, dizziness, abdominal pain, vomiting or diarrhoea
- Toxic envenomation symptoms after multiple stings: headache, vomiting, diarrhoea, collapse
- Persistent itch/distress in infestations (for example bed bugs, fleas, lice, scabies)
Signs
- Visible retained bee stinger/venom sac in skin
- Papules/macules/nodules; excoriations from scratching
- Flea bites often clustered below the knees
- Bed bug lesions on exposed skin, sometimes with haemorrhagic punctum; grouped/linear pattern
- Tick attached to skin or residual local papule/nodule after removal
- Spider bite may show two puncture marks
- Features of severe systemic reaction: angio-oedema, bronchospasm/stridor, hypotension, tachycardia, reduced consciousness
Investigations
Management
Lifestyle Modifications
- Remove visible bee stinger immediately (scrape/wipe off; do not delay for technique)
- Remove ticks promptly with fine-tipped forceps/tick remover, grasping close to skin and pulling steadily
- Clean area with soap/water, apply cold compress, elevate if swollen, avoid scratching, keep nails short
- Avoid triggers: shoes outdoors, protective clothing, insect repellents, bed/pet de-infestation where relevant
- Safety-net urgently for breathing difficulty, airway symptoms, widespread urticaria, syncope, or rapidly worsening swelling
- Urgent hospital assessment for stings in mouth/throat/tongue, peri-orbital stings threatening vision, severe immunocompromise with infection, systemic toxicity, or concerning travel-related bites
Pharmacological Treatment
Analgesia
- Paracetamol 500 mg-1 g orally every 4-6 hours as needed (max 4 g/day adult)
- Ibuprofen 200-400 mg orally up to three times daily with food (adult, if suitable)
Use lowest effective dose for shortest duration. Avoid NSAIDs in active peptic ulcer disease, significant renal impairment, NSAID-sensitive asthma, or high GI bleed risk unless protected/clinically justified.
Antihistamines for itch/urticaria
- Cetirizine 10 mg orally once daily (adult)
- Chlorphenamine 4 mg orally every 4-6 hours when needed (max 24 mg/day adult)
Non-sedating agents are preferred for daytime use. Chlorphenamine can cause sedation and anticholinergic effects; caution with driving, older adults, angle-closure glaucoma, and urinary retention risk.
Topical corticosteroid for local inflammatory reactions
- Hydrocortisone 1% cream/ointment thinly 1-2 times daily for up to 7 days
Avoid prolonged continuous use, broken/infected skin, and peri-ocular misuse. If reaction is very extensive or function-limiting, short oral corticosteroid courses may be considered by experienced clinicians.
Antibiotics (only if secondary bacterial infection/cellulitis)
- Flucloxacillin 500 mg orally four times daily for 5-7 days (adult)
- Clarithromycin 500 mg orally twice daily for 5-7 days if penicillin allergy (adult)
Do not prescribe routinely for non-infected bites/stings. Reassess if worsening, systemic features, immunocompromise, or poor response. Check allergy history and interaction profile.
Emergency treatment of anaphylaxis
- Adrenaline (epinephrine) 1 mg/mL (1:1000) 500 micrograms IM (0.5 mL) into anterolateral thigh in adults; repeat every 5 minutes if needed
No absolute contraindication in life-threatening anaphylaxis. Arrange immediate emergency transfer and airway/circulation support. Patients with prior systemic sting reactions should be referred for specialist allergy assessment and consideration of venom immunotherapy.
Surgical / Interventional
- Immediate mechanical removal of retained stinger
- Tick extraction with dedicated remover/fine forceps (complete mouthpart removal when possible)
- Incision and drainage if a secondary abscess develops
Complications
- Large local hypersensitivity reactions (>10 cm oedema/erythema/pruritus)
- Systemic allergic reactions including anaphylaxis
- Systemic toxic reaction after multiple stings (hypotension, shock, GI symptoms)
- Secondary bacterial infection (cellulitis, impetigo, abscess)
- Vector-borne infection risk (for example Lyme disease after tick bite)
- Exacerbation of atopic eczema and papular urticaria
- Psychological distress/sleep disturbance from infestations
- Rare delayed immune complications (serum sickness-like illness, vasculitis, neuritis, encephalitis, nephrosis)
Prognosis
Most uncomplicated bites resolve within hours and most stings over hours to a few days. Large local sting reactions usually settle in 3-10 days; after a prior large local reaction, future systemic reaction risk is approximately 4-10%. Severe systemic reactions are uncommon but clinically important (about 0.4-0.8% in children and up to 3% in adults), and recurrence risk is high after prior sting anaphylaxis (up to about 70%). Persistent lesions can occur with retained tick parts or ongoing untreated infestation.
Sources & References
🏥BMJ Best Practice(1)
💊BNF Drug References(4)
- Ceftriaxone[management.pharmacological]
- Co-amoxiclav[management.pharmacological]
- Doxycycline[management.pharmacological]
- Metronidazole[management.pharmacological]
✅NICE Guidelines(1)
- Insect bites and stings[overview]
📖Textbook References(20)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1567)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1673)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1518)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1553)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1553)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1647)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1567)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1517)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1673)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1504)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 408)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1549, 1550)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 155)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 44)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 431, 432)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 88)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 141)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 44)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 91)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 56)[context]