Scabies

Scabies is a cutaneous infestation caused by the mite Sarcoptes scabiei var hominis, which completes its ~14-day life cycle in the human epidermis. It is primarily a clinical diagnosis characterized by intense pruritus and a characteristic distribution of papules, burrows, and excoriations. [1]

The following table from JAMA summarizes key clinical features and treatment comparisons:

1. History

• Pruritus: Intense, generalized, characteristically worse at night; onset typically 4–6 weeks after primary infestation (may be shorter with reinfestation) [1-2]
• Timing/triggers: Ask about recent onset of itch, nocturnal predominance, and whether itch preceded the rash
• Contact history: Household members, sexual partners, bed-sharing contacts, caregiving roles, institutional living (shelters, nursing homes, prisons) with similar symptoms [1]
• Prior treatment: Any topical steroids (can mask morphology and blunt pruritus), prior scabicides, or self-treatment attempts [1]
• Associated symptoms: Scratching-related skin breakdown, signs of secondary infection (pustules, crusting, warmth)
• Important negatives: No history of atopy or contact dermatitis, no new exposures to irritants/allergens

2. Alarm Features

• Crusted (Norwegian) scabies: Diffuse hyperkeratotic/psoriasiform plaques, often with minimal pruritus — highly contagious (thousands to millions of mites); associated with immunosuppression (systemic steroids, methotrexate, cyclosporine), HIV, HTLV-1, neurological conditions [1][3]
• Secondary bacterial infection: Impetigo, cellulitis, abscesses, necrotizing soft tissue infection, bacteremia/sepsis — particularly dangerous in crusted scabies [1][3]
• Poststreptococcal complications: In endemic settings, streptococcal superinfection of scabietic lesions is associated with acute poststreptococcal glomerulonephritis and rheumatic fever [1]
• Erythroderma: Disseminated erythematous, scaly rash involving atypical areas (scalp, head, neck, back) suggests profuse/severe scabies [3]
• Systemic toxicity: Fever, fluid/electrolyte disturbances in severe crusted scabies — can be life-threatening [3]

3. Medications

Treatments (common scabies)

• Permethrin 5% cream (first-line): Apply neck-to-toes (scalp-to-toes in infants/young children) for 8–14 hours, wash off; repeat in 1–2 weeks [1][4]
• Oral ivermectin 200 µg/kg: Take with food (increases bioavailability); repeat in 14 days; not FDA-approved for scabies but widely used [1][4]
• Spinosad 0.9% topical suspension: FDA-approved alternative [1]
• Crotamiton 10% cream/lotion: FDA-approved but lower efficacy [1]

Crusted scabies: Combination oral ivermectin + topical permethrin + keratolytic agent (urea or salicylic acid), with more frequent dosing [1][3]

Medication cautions

• Ivermectin: Limited safety data in pregnancy and children <15 kg; drug interactions with azithromycin, TMP-SMX, cetirizine; safety unknown with multiple doses in severe liver disease [1][4]
• Lindane 1%: Alternative only if recommended therapies fail — risk of seizures, aplastic anemia; contraindicated in pregnancy, breastfeeding, children <10 years, extensive dermatitis [4]
• Topical steroids: May be used for irritant contact dermatitis from permethrin or postscabetic itch, but should not be used before diagnosis is confirmed (masks findings) [1]
• Antihistamines: Scabietic itch is not histamine-mediated, but sedating first-generation antihistamines may reduce nocturnal scratching [1]

4. Diet

• Ivermectin should be taken with food to increase bioavailability and epidermal drug penetration [4]
• No specific dietary triggers or restrictions for scabies itself
• Adequate hydration and nutrition support skin healing, particularly in elderly or debilitated patients with crusted scabies

5. Review of Systems

• Dermatologic: Rash distribution, pruritus severity, skin breakdown, signs of secondary infection
• Infectious: Fever, chills, malaise (suggests secondary bacterial infection or sepsis)
• Renal: Hematuria, edema, decreased urine output (poststreptococcal glomerulonephritis in endemic settings)
• Cardiovascular: Joint pain, chest pain (rheumatic fever — rare, in endemic populations) [1]
• Immunologic: History of HIV, transplant, immunosuppressive medications
• Psychiatric/social: Sleep disruption, psychosocial distress, stigma

6. Collateral History and Family History

• Household contacts: Ask whether others in the home have pruritus or rash — simultaneous treatment of all contacts is essential even if asymptomatic [5]
• Sexual contacts: Scabies is considered a sexually transmitted ectoparasitic infection; CDC guidelines recommend screening for other STIs in appropriate settings [6]
• Institutional exposure: Nursing home, shelter, prison, daycare — outbreaks are common in these settings [3]
• Family history: No hereditary predisposition, but familial clustering reflects shared living conditions
• Immunosuppression in household: Identify immunocompromised contacts at risk for crusted scabies

7. Risk Factors

• Overcrowded living conditions (shelters, dormitories, prisons, refugee camps) [1]
• Prolonged skin-to-skin contact (≥15–20 minutes typically required for transmission) [1]
• Immunosuppression: Systemic glucocorticoids, methotrexate, cyclosporine, HIV, HTLV-1 — major risk for crusted scabies [1]
• Neurological conditions: Alzheimer disease, spinal cord injury (impaired sensation/inability to scratch) [1]
• Extremes of age: Infants and elderly
• Socioeconomic disadvantage: Limited access to hygiene facilities, healthcare [7]
• Sexual contact and bed-sharing [1]

8. Differential Diagnosis

• Atopic dermatitis: Chronic eczematous changes, personal/family history of atopy; distribution differs (flexural predominance)
• Contact dermatitis (allergic or irritant): Exposure history, distribution correlates with contactant
• Dyshidrotic eczema: Vesicles on palms/soles; no burrows
• Dermatitis herpetiformis: Grouped vesicles on extensor surfaces; associated with celiac disease
• Bullous pemphigoid: Tense bullae in elderly; can mimic bullous scabies
• Cutaneous T-cell lymphoma: Chronic pruritic patches/plaques; biopsy distinguishes
• Insect bites/papular urticaria: Exposed areas, no burrows, no household clustering
• Pediculosis (body lice): Lesions under clothing seams, lice/nits on clothing [1]
• Prurigo nodularis: Dome-shaped nodules from chronic scratching — can coexist with scabies
• Psoriasis: Crusted scabies can closely mimic psoriasis [1][8]

9. Past Medical History

• Prior scabies episodes: Reinfestation produces faster symptom onset (1–3 days vs. 4–6 weeks)
• Immunosuppressive conditions: HIV/AIDS, organ transplant, hematologic malignancy
• Immunosuppressive medications: Steroids, biologics, chemotherapy
• Neurological conditions: Dementia, neuropathy (risk for crusted scabies)
• Chronic skin conditions: Atopic dermatitis, psoriasis (may complicate diagnosis and treatment)
• Renal/hepatic disease: Relevant for ivermectin dosing considerations [4]

10. Physical Exam

Key findings

• Burrows: Pathognomonic — curvilinear, thread-like lesions ending in a vesicle or erosion (mite location) [1]
• Papules and excoriations: Erythematous, often excoriated papules
• Distribution: Interdigital web spaces, volar wrists, ankles, axillae, buttocks, male genitalia, areolae [1]
• Nodular scabies: Firm pink-to-hyperpigmented nodules, especially on male genitalia or in infants [1]
• Crusted scabies: Thick, hyperkeratotic plaques on scalp, face, digits, nails, periumbilical area [1]

Focused exam maneuvers

• Dermoscopy: Look for "delta-wing jet" sign — brown triangular structure at burrow end representing the mite [1]
• Ink test: Apply ink to suspected burrow, wipe off — ink tracks along burrow
• Examine all predilection sites systematically, including genitalia

Concerning findings

• Signs of secondary infection: pustules, honey-colored crusting, warmth, lymphangitis
• Widespread hyperkeratosis suggesting crusted scabies

11. Lab Studies

• Routine labs are not required for diagnosis of common scabies [1]
• Peripheral eosinophilia: Observed in common scabies; present in 58% of hospitalized crusted scabies patients (median AEC 1.6 × 10⁹/L) [1]
• CBC with differential: If secondary infection or crusted scabies suspected
• BMP: In severe crusted scabies with concern for fluid/electrolyte disturbances [3]
• Blood cultures: If signs of bacteremia/sepsis
• HIV testing: Should be considered in crusted scabies without known immunosuppression [1]
• HTLV-1 testing: Consider in patients from endemic regions (Caribbean, South America, southern Japan, Africa) with crusted scabies [1]
• Streptococcal markers (ASO, anti-DNase B, urinalysis): If concern for poststreptococcal complications in endemic settings [1]

12. Imaging

• Imaging is generally not indicated for scabies
• Consider imaging only if complications arise (e.g., deep soft tissue infection requiring CT/MRI, echocardiography if rheumatic heart disease suspected in endemic populations)

13. Special Tests

• Skin scraping with mineral oil microscopy: Gold standard confirmation — visualize mites, eggs, or scybala (feces) under light microscopy. High-yield sites: palm/sole creases, lateral hands/feet, volar wrists, ankles, interdigital web spaces [1]
• Dermoscopy: Noninvasive; identifies burrows and the "delta-wing jet" sign (brown triangular mite head) [1]
• 2020 IACS Consensus Diagnostic Criteria: [1]
  • Confirmed: Mites/eggs/feces on microscopy or dermoscopy
  • Clinical: Burrows, typical genital lesions in men, or typical lesions + typical distribution + 2 historical features (itch, positive contact history)
  • Suspected: Typical lesions + typical distribution + 1 historical feature
• Videodermoscopy / reflectance confocal microscopy: Advanced imaging for difficult cases [1]

14. ECG

• Not routinely indicated
• Consider ECG only if concern for rheumatic carditis in endemic populations with poststreptococcal complications

15. Assessment

Severity stratification

• Common scabies: Low mite burden (<15 mites in ~80% of cases), intense pruritus, typical distribution [1-2]
• Profuse scabies: Disseminated erythematous/scaly rash involving atypical areas (scalp, back, neck) [3]
• Crusted scabies: Hyperkeratotic plaques, thousands to millions of mites, highly contagious, often in immunocompromised patients [1][3]

Complications to consider

• Secondary bacterial infection (Group A Strep, S. aureus) → impetigo, cellulitis, abscess, sepsis [1]
• Postscabetic pruritus (itch persisting weeks after successful treatment due to residual mite allergens) [2]
• Poststreptococcal glomerulonephritis and rheumatic fever (in endemic settings) [1]
• Institutional outbreaks from unrecognized crusted scabies [3]

16. Treatment Plan

Common scabies — first-line

• Permethrin 5% cream: Apply to entire body (neck down in adults; head-to-toe in infants/children) for 8–14 hours, then wash off. Repeat in 7–14 days. A recent cluster RCT showed permethrin superiority over oral ivermectin (cluster cure 88.5% vs. 71.8%) [1][4][9]
• OR Oral ivermectin 200 µg/kg with food, repeat in 14 days [4]

Adjunctive measures

• Midpotency topical corticosteroids for irritant dermatitis or postscabetic itch [1]
• Sedating antihistamines (e.g., hydroxyzine) for nocturnal pruritus [1]
• Treat all household contacts and sexual partners simultaneously, even if asymptomatic [5]

Crusted scabies

• Combined therapy: Oral ivermectin 200 µg/kg (multiple doses on days 0, 1, 7, 8, 14 ± days 21, 28 depending on severity) + topical permethrin every 2–3 days for 1–2 weeks + keratolytic agent (urea/salicylic acid) + daily emollient [1][3]
• Standard-dose ivermectin (200 µg/kg) appears as effective as higher-dose (400 µg/kg) when combined with permethrin [3]

Environmental decontamination

• Launder clothing/linens in hot water ≥130°F with high-heat drying cycle [5]
• Items that cannot be laundered: seal in plastic bag for ≥72 hours [5]

17. Disposition

Discharge (vast majority)

• Common scabies is managed entirely as an outpatient
• Prescribe treatment, provide written instructions on proper application, and ensure contact treatment plan

Admission criteria

• Severe crusted scabies with systemic complications (sepsis, fluid/electrolyte disturbances, extensive secondary infection) [3]
• Inability to perform self-care or apply topical treatment (consider social admission or home health)
• Erythroderma with hemodynamic instability

Observation

Specialist consultation triggers

• Dermatology: Crusted scabies, treatment failure, diagnostic uncertainty, atypical presentations
• Infectious disease: Crusted scabies with secondary sepsis, HIV/HTLV-1 workup
• Infection control: Institutional outbreaks [3]

18. Follow Up / Return Precautions

Follow-up timing

• Reassess 2–4 weeks after completing treatment to confirm clinical cure [9]
• Pruritus may persist for 2–4 weeks after successful treatment (postscabetic itch from residual mite allergens) — this does not necessarily indicate treatment failure [2]

Return precautions — advise patients to return if

• Pruritus worsening or new lesions appearing >4 weeks after treatment
• Signs of secondary infection: increasing redness, warmth, swelling, pus, fever
• Spread of rash to new areas or development of thick, crusted plaques

Patient counseling

• Emphasize that all contacts must be treated simultaneously to prevent reinfestation [5]
• Itch will likely persist for weeks after treatment — this is expected and does not mean treatment failed
• Avoid skin-to-skin contact until treatment is complete
• Complete environmental decontamination of clothing and linens [5]
• If symptoms persist beyond 4 weeks, return for re-evaluation and possible retreatment

References

1. Scabies, Bedbug, and Body Lice Infestations: A Review. — Thomas C, Castillo Valladares H, Berger TG, Chang AY. The Journal of the American Medical Association. 2024.

2. Immune mechanisms in human Sarcoptes scabiei (Acari: Sarcoptidae) infestations. — Gazi U, Taylan-Ozkan A, Mumcuoglu KY. Parasite Immunology. 2022.

3. Combined Oral Ivermectin and 5% Permethrin Cream to Treat Severe Scabies. — Bernigaud C, Do-Pham G, Guichard E, et al. The New England Journal of Medicine. 2026.

4. Sexually Transmitted Infections Treatment Guidelines, 2021. — Workowski KA, Bachmann LH, Chan PA, et al. MMWR. Recommendations and Reports : Morbidity and Mortality Weekly Report. Recommendations and Reports. 2021.

5. What Is Scabies?. — Roberts K. The Journal of the American Medical Association. 2025.

6. Scabies. — Chosidow O. The New England Journal of Medicine. 2006.

7. Scabies: A Clinical Update. — Iyengar L, Chong AH, Steer AC. The Medical Journal of Australia. 2024.

8. Chronic Pruritus: A Review. — Butler DC, Berger T, Elmariah S, et al. The Journal of the American Medical Association. 2024.

9. Oral Ivermectin Versus 5% Permethrin Cream to Treat Children and Adults With Classic Scabies: Multicentre, Assessor Blinded, Cluster Randomised Clinical Trial. — Boralevi F, Simon G, Bernigaud C, et al. BMJ. 2026.