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InfestationCommon DDxICD-10 B86

Scabies (including crusted)

Sarcoptes scabiei infestation · Norwegian scabies (crusted variant)

Scabies is a human ectoparasitosis caused by Sarcoptes scabiei var. hominis. UK incidence is rising — both classical scabies and the highly contagious crusted (Norwegian) variant which occurs principally in elderly, frail, institutionalised or immunosuppressed patients. Scabies is a daily DDx for atopic dermatitis, prurigo nodularis, urticaria, cutaneous T-cell lymphoma, drug eruption and immune-checkpoint-inhibitor pruritus. UK BAD 2019 guidelines and NICE CKS guidance set out the diagnostic and treatment framework.

CurrentLast reviewed 16 May 2026
Clinical image of Scabies (including crusted)
Scabies (including crusted). Image sourced from DermNet New Zealand. Used under CC BY-NC-ND 4.0. No endorsement implied.

Biology and transmission

  • Sarcoptes scabiei var. hominis: 0.3-0.5 mm female mite burrows into stratum corneum, laying eggs over 30 days.
  • Mite load: ~10-20 in classical scabies; thousands to millions in crusted (Norwegian) scabies.
  • Transmission: prolonged skin-to-skin contact (sexual, familial, care-givers); fomites (clothing / bedding) for crusted scabies.
  • Incubation: 4-6 weeks first exposure; days on re-infestation.

Clinical features

  • Classical scabies:
    • Intense pruritus, worse at night.
    • Burrows: 5-10 mm linear / serpiginous greyish ridges with terminal vesicle; finger webs, wrist flexors, axillae, areola, periumbilical, genitalia, buttocks.
    • Excoriated papules, eczematised plaques; often spares face / scalp in adults (involved in infants).
    • Nodular scabies: persistent itchy nodules on genitals / axillae after treatment.
  • Crusted (Norwegian) scabies:
    • Hyperkeratotic plaques on hands / feet / scalp / nails.
    • Often minimal pruritus despite massive mite burden.
    • Risk groups: elderly / frail, dementia, HIV, HTLV-1, organ transplant, immune-checkpoint inhibitors, long-term corticosteroids, immunosuppressive biologics, Down syndrome.
    • Highly contagious — outbreak source in care homes / hospitals.

Investigations

  • Clinical diagnosis with the suspect history + burrow / itch / contact.
  • Dermoscopy: "delta-wing" or "jet plane with contrail" sign — mite head + S-shaped burrow.
  • Skin scraping + KOH or oil mount → mite / eggs / scybala on microscopy.
  • Reflectance confocal microscopy if available.
  • Burrow ink test: ink applied, wiped off, residual track within burrow.
  • Bloods: in crusted disease consider HIV / HTLV-1 / immunoglobulins.

Differentials

  • Atopic eczema flare — distribution differs; less burrow.
  • Prurigo nodularis — chronic, isolated nodules; biopsy.
  • Urticaria, papular urticaria.
  • Drug eruption / ICI pruritus — medication history.
  • Bullous pemphigoid (urticarial phase) — elderly; biopsy.
  • Mycosis fungoides, particularly in older adults with chronic pruritus.
  • Bedbug / flea bites — three-in-a-row breakfast / lunch / dinner pattern.
  • Pediculosis.

Management (BAD 2019 / NICE CKS)

  • Classical scabies:
    • 5% permethrin cream — whole body neck-down (and scalp / face in children); leave 8-12 h; rinse; repeat at day 7-14.
    • Alternative: malathion 0.5% aqueous lotion.
    • Oral ivermectin 200 µg/kg single dose, repeated at day 7-14 — useful for outbreak control, treatment failure or topical-resistant disease.
  • Crusted scabies:
    • Combination: oral ivermectin 200 µg/kg on days 1, 2, 8, 9, 15 ± 22 + topical permethrin + keratolytic (5-10% salicylic acid).
    • Isolation / infection-prevention measures.
  • Contacts: treat all household and intimate / sexual contacts simultaneously, irrespective of symptoms.
  • Environmental:
    • Hot wash (≥50 °C) bedding / clothing / towels.
    • Bag items unwashable for 72 h (mites die without host).
  • Counsel patients about post-scabietic pruritus persisting 2-4 weeks despite successful eradication (continue emollients, antihistamines).

References

  1. Salavastru CM et al. European guideline for the management of scabies. J Eur Acad Dermatol Venereol. 2017;31:1248-1253.
  2. British Association of Dermatologists. Scabies — patient information leaflet. London: BAD; 2019.
  3. NICE CKS. Scabies. London: NICE; accessed 18 May 2026.
  4. Engelman D, Steer AC. Control strategies for scabies. Trop Med Infect Dis. 2018;3:98.
  5. Roberts LJ et al. Crusted scabies: clinical and immunological findings in seventy-eight patients. Int J Dermatol. 2005;44:135-141.

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