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Microbiology · Ectoparasites

Sarcoptes scabiei !

  • Parasite
  • Contact
  • Exam priority: high

A tiny mite that burrows into the skin and causes intense itch, worse at night. It spreads by skin-to-skin contact and affects whole families.

Updated 2026-11-01

Also called: itch mite, scabies mite

At a glance

Shape
Round, eyeless body with 4 pairs of short legs
Family
Sarcoptidae
Type
Mite (arthropod, arachnid), obligate ectoparasite
Size
Female 0.3–0.45 mm; male about half that size

Morphology

  • Female living in a serpiginous burrow in the stratum corneum.
  • Oval eggs and faeces (scybala) inside the burrow, visible in scrapings.
  • Larva with 3 pairs of legs; nymph and adult with 4 pairs.

Transmission

  • Prolonged skin-to-skin contact: household members, sexual partners, carers.
  • Less often, shared bedding or clothing.
  • In crusted scabies, with thousands of mites, clothing, beds and furniture also spread it.

Reservoir: Humans (animal varieties cause only transient infestation)

Isolation precautions

What the care team adds to standard precautions.

Contact
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

Life cycle

  1. The fertilised female digs a serpiginous burrow in the stratum corneum and lays 2–3 eggs a day.
  2. Eggs hatch in 3–4 days; the six-legged larva comes to the surface.
  3. The larva digs short moulting pouches and becomes an eight-legged nymph.
  4. The nymph moults into an adult; males and females mate once on the skin.
  5. The female digs a permanent burrow and lays eggs for the rest of her life, 1–2 months.
  6. Spread happens when a fertilised female passes to another person by skin-to-skin contact.

Virulence factors

  • The itch is a hypersensitivity reaction to mites, eggs and faeces.
  • With a first infestation symptoms take weeks to appear; with reinfestation, a few days.
  • Scratching opens the way to impetigo by S. aureus and S. pyogenes, with a risk of post-streptococcal glomerulonephritis.
  • In immunocompromised, elderly or institutionalised people, crusted scabies develops with thousands of mites.

Diseases it causes

  • Scabies Scabies →
  • Crusted (Norwegian) scabies in immunocompromised, elderly or institutionalised people

Clinical picture

  • Intense itch, worse at night, in several household members.
  • Burrows and papules in finger webs, wrists, axillae, waist, genitals and areolae.
  • In infants also palms, soles and scalp.
  • Crusted scabies: thick crusts with little itch.

Diagnosis

  • Clinical diagnosis from lesion distribution, burrows and family itch.
  • Scraping of a burrow with mineral oil: mites, eggs or scybala under the microscope.
  • Extracting the mite from the end of the burrow with a needle.
  • Dermoscopy: the mite seen at the end of the burrow.

Treatment

Topical scabicides (permethrin, benzyl benzoate, sulphur ointment, malathion) or oral ivermectin; all contacts are treated at the same time. Crusted scabies needs combined therapy with keratolytics, and impetigo needs antibiotics.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Treat household members and close contacts at the same time.
  • Hot-wash clothing and bedding used in the previous days, or seal them in a bag for several days.
  • Contact precautions in hospitals and care homes.
  • Mass ivermectin administration in high-prevalence communities.

Test yourself

Think of the answer, then tap the question to see it.

Which isolation precautions does a patient with scabies need?

Contact precautions, on top of standard precautions.

Why are all household members treated at the same time?

To stop mites passing back to the person already treated and keeping the reinfestation going.

Which form of scabies is highly contagious and seen in immunocompromised people?

Crusted (Norwegian) scabies, with thick crusts holding thousands of mites.

Which kidney complication is linked to scabies?

Post-streptococcal glomerulonephritis after Streptococcus pyogenes impetigo.

How is scabies confirmed in the laboratory?

With a burrow scraping showing mites, eggs or scybala under the microscope.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Scabies (CDC, 2024); Scabies (WHO, 2023); About Scabies | Scabies | CDC (CDC, 2024).

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Representative model, for educational purposes only.