Scabies

Scabies is a highly contagious skin infestation caused by the microscopic mite Sarcoptes scabiei var. hominis. These tiny parasites burrow into the upper layer of skin to live and lay eggs, causing intense itching and a characteristic rash. Scabies spreads easily through direct skin-to-skin contact and can affect people of all ages and backgrounds. Without treatment, the infestation persists indefinitely and can lead to secondary complications such as bacterial skin infections.

Medical Disclaimer: This information is for educational purposes only and should not replace professional medical advice. If you suspect you have scabies or experience persistent itching and rash, seek medical attention for proper diagnosis and treatment.

Overview

Scabies is one of the most common parasitic skin infestations worldwide, affecting an estimated 300 million people annually. The causative organism, Sarcoptes scabiei, is an eight-legged mite barely visible to the naked eye, measuring only 0.3-0.4 mm in length. Female mites burrow into the stratum corneum (outermost layer of skin) where they create tunnels and lay 2-3 eggs daily for up to 6 weeks.

The characteristic intense itching associated with scabies is not caused by the mites themselves, but rather by the body's allergic reaction to the mites, their eggs, and their waste products. This delayed hypersensitivity reaction typically develops 2-6 weeks after initial infestation in people who have never had scabies before, but may occur within 24-48 hours in those previously infected.

Scabies affects people of all socioeconomic levels and is found in both developed and developing countries. It is particularly common in crowded conditions such as nursing homes, hospitals, childcare centers, and correctional facilities. The condition does not discriminate based on personal hygiene, though it may be more severe in individuals with compromised immune systems.

Symptoms

Scabies symptoms result from the body's immune response to the mites and their byproducts. The hallmark symptom is intense itching, which typically worsens at night when the mites are most active.

Primary Symptoms

Characteristic Lesions

  • Burrows: Thin, irregular, thread-like lines 2-15mm long
  • Papules: Small, red, raised bumps
  • Vesicles: Small fluid-filled blisters
  • Pustules: Pus-filled bumps (secondary to scratching)
  • Excoriations: Scratch marks and crusts
  • Nodules: Larger, persistent lumps (especially in genital area)

Common Locations

  • Finger webs: Between fingers
  • Wrists and forearms: Flexural surfaces
  • Elbows: Around elbow creases
  • Armpits: Axillary folds
  • Waistline: Belt area and lower abdomen
  • Genital area: Penis, scrotum, vulva
  • Buttocks: Especially the cleft
  • Feet: Soles and between toes
  • Ankles: Around ankle bones

Age-Specific Presentations

Infants and Young Children

  • Face and scalp involvement (rare in adults)
  • Palms and soles commonly affected
  • Vesicular or pustular lesions
  • Irritability and sleep disturbance
  • Failure to thrive in severe cases

Elderly or Immunocompromised

  • Norwegian (crusted) scabies - thick, crusty scales
  • Widespread distribution
  • Minimal itching despite heavy infestation
  • Highly contagious variant

Associated Symptoms

  • Problems during pregnancy - complications if infected while pregnant
  • Unpredictable menstruation - stress-related hormonal changes
  • Sleep disturbance due to nighttime itching
  • Restlessness and irritability
  • Secondary bacterial infection signs
  • Lymph node enlargement

Complications

  • Secondary bacterial infection: Impetigo, cellulitis
  • Post-scabetic dermatitis: Persistent inflammation after treatment
  • Scarring: From excessive scratching
  • Hyperpigmentation: Dark spots after healing
  • Kidney complications: Post-streptococcal glomerulonephritis (rare)

Causes

Scabies is caused exclusively by infestation with the human scabies mite, Sarcoptes scabiei var. hominis. Understanding the mite's life cycle and transmission methods is crucial for effective treatment and prevention.

The Scabies Mite

Sarcoptes scabiei var. hominis

  • Size: Adult females 0.3-0.4 mm, males 0.2-0.3 mm
  • Appearance: Oval, light-colored, eight-legged arthropod
  • Lifespan: 30-60 days on human host
  • Survival off host: 24-36 hours at room temperature
  • Host specificity: Adapted specifically to humans

Life Cycle

  1. Mating: Occurs on skin surface
  2. Burrowing: Fertilized female creates tunnel in stratum corneum
  3. Egg laying: 2-3 eggs laid daily for 4-6 weeks
  4. Hatching: Eggs hatch in 3-4 days
  5. Larval stage: Six-legged larvae migrate to skin surface
  6. Nymphal stages: Two eight-legged nymphal stages
  7. Adult stage: Reached in 10-14 days, ready to mate

Transmission Mechanisms

Direct Transmission

  • Skin-to-skin contact: Primary mode of transmission
  • Duration required: Usually 15-20 minutes of direct contact
  • Sexual contact: Common route among sexually active adults
  • Household contact: Family members, caregivers
  • Institutional contact: Healthcare facilities, nursing homes

Indirect Transmission

  • Clothing and bedding: Possible but less common
  • Furniture and carpets: Temporary survival on surfaces
  • Shared towels: Risk in close-contact settings
  • Time limitation: Mites die within 24-36 hours off human host

Risk Factors for Transmission

High-Risk Situations

  • Crowded living conditions:
    • Nursing homes and assisted living facilities
    • Hospitals and healthcare settings
    • Childcare centers and schools
    • Homeless shelters
    • Military barracks
    • Correctional facilities
  • Intimate contact situations:
    • Sexual partners
    • Family members sharing beds
    • Parents caring for infants
    • Healthcare workers providing hands-on care

Host Factors

Susceptibility Factors

  • Immunocompromised states:
    • HIV/AIDS
    • Cancer chemotherapy
    • Organ transplant recipients
    • Chronic corticosteroid use
    • Malnutrition
  • Age extremes:
    • Very young children
    • Elderly individuals
    • Physically disabled persons

Environmental Factors

  • Temperature: Mites thrive in warm environments
  • Humidity: Moderate humidity favors survival
  • Overcrowding: Facilitates transmission
  • Poor sanitation: May contribute to secondary complications
  • Limited resources: Delays in diagnosis and treatment

Reinfection and Persistence

  • Treatment failure: Incorrect application or resistance
  • Reinfection: Contact with untreated individuals
  • Environmental contamination: Surviving mites in bedding/clothing
  • Incomplete treatment: Not treating all household members
  • Delayed diagnosis: Continued transmission during incubation

Risk Factors

While anyone can get scabies regardless of age, hygiene, or socioeconomic status, certain factors increase the likelihood of infestation and complications.

High-Risk Populations

Institutional Settings

  • Nursing home residents: Close contact and shared care
  • Hospital patients: Especially long-term care units
  • Prison inmates: Crowded conditions and limited privacy
  • Homeless individuals: Shelter conditions and limited hygiene access
  • Military personnel: Barracks living and shared facilities

Healthcare Workers

  • Direct patient care: Nurses, assistants, therapists
  • Laundry staff: Handling contaminated linens
  • Housekeeping staff: Cleaning infected areas
  • Emergency responders: First aid and patient transport

Age-Related Risk Factors

Pediatric Population

  • Childcare attendees: Close contact during play
  • School-age children: Classroom and playground transmission
  • Infants and toddlers: Frequent caregiver contact
  • Foster children: Multiple placement settings

Elderly Population

  • Cognitive impairment: Difficulty reporting symptoms
  • Limited mobility: Dependence on caregivers
  • Medication effects: Immunosuppressive treatments
  • Skin changes: Age-related barrier dysfunction

Medical Risk Factors

Immunocompromising Conditions

  • HIV/AIDS: Increased risk of crusted scabies
  • Cancer: Especially with chemotherapy treatment
  • Organ transplantation: Immunosuppressive medications
  • Autoimmune diseases: Systemic lupus, rheumatoid arthritis
  • Diabetes mellitus: Impaired immune function

Skin Conditions

  • Atopic dermatitis: Compromised skin barrier
  • Psoriasis: Inflammatory skin condition
  • Contact dermatitis: Increased skin sensitivity
  • Xerosis: Dry skin conditions

Social and Environmental Risk Factors

Living Conditions

  • Overcrowded housing: Multiple people per room
  • Shared bedding: Family members sharing beds
  • Limited resources: Inability to wash clothes/bedding frequently
  • Temporary housing: Shelters, motels, hostels

Occupational Factors

  • Healthcare professions: Direct patient contact
  • Childcare workers: Contact with children
  • Social workers: Home visits and client contact
  • Emergency services: First responders

Behavioral Risk Factors

  • Sexual activity: Multiple or new partners
  • Poor hygiene practices: Limited access to washing facilities
  • Delayed medical care: Avoiding or unable to seek treatment
  • Non-compliance: Not following treatment instructions

Geographic and Seasonal Factors

  • Tropical climates: Year-round transmission
  • Winter months: Increased indoor crowding in temperate climates
  • Developing countries: Limited healthcare access
  • Conflict zones: Displaced populations and poor living conditions

Protective Factors

  • Good personal hygiene
  • Avoiding close contact with infected individuals
  • Regular laundering of clothes and bedding
  • Prompt medical attention for skin symptoms
  • Following treatment protocols completely
  • Treating all household contacts simultaneously

Diagnosis

Scabies diagnosis is primarily clinical, based on characteristic symptoms, physical examination findings, and epidemiological factors. Laboratory confirmation may be helpful but is not always necessary for treatment initiation.

Clinical Assessment

History Taking

  • Symptom timeline: Onset, duration, and progression of itching
  • Contact history: Exposure to infected individuals
  • Living situation: Household members, institutional settings
  • Previous treatments: Over-the-counter or prescription attempts
  • Medical history: Immunocompromising conditions
  • Travel history: Recent travel to endemic areas

Physical Examination

Inspection Techniques

  • Good lighting: Natural light or bright examination light
  • Magnification: Magnifying glass or dermatoscope
  • Systematic approach: Examine all body areas methodically
  • Focus areas: Finger webs, wrists, genitals, feet

Key Findings

  • Burrows: Pathognomonic sign when present
  • Distribution pattern: Characteristic locations
  • Excoriations: Evidence of scratching
  • Secondary infection: Pustules, crusting, cellulitis
  • Family involvement: Similar symptoms in contacts

Laboratory Diagnosis

Microscopic Examination

  • Skin scrapings:
    • Scrape burrow with sterile blade
    • Add mineral oil or KOH
    • Examine under low power (10x)
    • Look for mites, eggs, or fecal pellets
  • Burrow ink test:
    • Apply ink over suspected burrow
    • Wipe surface clean
    • Ink remains in burrow tunnel
    • Scrape and examine microscopically

Dermoscopy

  • Jet contrail sign: Dark triangular structure (mite) at burrow end
  • Burrow visualization: Linear or curved structures
  • Real-time examination: Can see mite movement
  • Non-invasive: No need for skin scraping

Diagnostic Criteria

Major Criteria (2 or more required)

  • Intense pruritus, especially nocturnal
  • Characteristic distribution of lesions
  • Microscopic identification of mites, eggs, or feces
  • Response to scabicidal treatment

Minor Criteria (supportive evidence)

  • Contact with confirmed scabies case
  • Presence of burrows
  • Typical lesion morphology
  • Institutional outbreak setting

Differential Diagnosis

Healthcare providers must distinguish scabies from other itchy skin conditions:

  • Atopic dermatitis: Different distribution, family history
  • Contact dermatitis: Clear relationship to allergen/irritant
  • Seborrheic dermatitis: Greasy scales, different locations
  • Psoriasis: Well-defined plaques with silvery scales
  • Insect bites: Seasonal pattern, different distribution
  • Drug reactions: Temporal relationship to medication
  • Urticaria: Transient wheals, different appearance
  • Folliculitis: Hair follicle involvement

Special Considerations

Crusted (Norwegian) Scabies

  • Clinical presentation: Thick, hyperkeratotic plaques
  • Mite burden: Thousands to millions of mites
  • Minimal itching: Due to immunosuppression
  • High contagiosity: Massive mite shedding
  • Diagnosis: Skin biopsy may be needed

Pediatric Considerations

  • Atypical distribution: Face and scalp involvement
  • Vesiculobullous lesions: More common in infants
  • Secondary infection: Higher risk of complications
  • Behavioral changes: Irritability, sleep disturbance

Diagnostic Challenges

  • Low mite burden: May be difficult to find mites
  • Secondary changes: Scratching obscures primary lesions
  • Previous treatment: May alter clinical appearance
  • Coexisting conditions: Other skin diseases complicate diagnosis
  • Nodular scabies: Persistent nodules after treatment

Treatment Options

Effective scabies treatment requires appropriate scabicidal therapy for the patient and all close contacts, along with environmental decontamination measures. Treatment should be initiated promptly to prevent spread and complications.

First-Line Topical Treatments

Permethrin 5% Cream

  • Dosing: Apply to entire body from neck down
  • Duration: Leave on for 8-14 hours, then wash off
  • Repeat: Second application after 1-2 weeks if needed
  • Safety: Safe for children >2 months and pregnant women
  • Efficacy: 90-95% cure rate

Benzyl Benzoate 25%

  • Application: Apply to entire body for 3 consecutive days
  • Duration: Leave on for 24 hours each application
  • Dilution: May dilute to 12.5% for children
  • Side effects: Skin irritation more common

Alternative Topical Treatments

Sulfur Ointment 5-10%

  • Use: Safe for infants under 2 months and pregnancy
  • Application: Daily for 3-7 days
  • Disadvantages: Messy, odorous, may stain clothing
  • Efficacy: Variable, lower than permethrin

Crotamiton 10%

  • Application: Daily for 2-5 days
  • Additional benefit: Antipruritic effect
  • Efficacy: Lower than permethrin
  • Use: Alternative when first-line unavailable

Oral Systemic Treatment

Ivermectin

  • Dosing: 200 μg/kg body weight (single dose)
  • Repeat: Second dose after 1-2 weeks
  • Indications:
    • Crusted scabies
    • Immunocompromised patients
    • Treatment failure with topicals
    • Institutional outbreaks
    • Widespread disease
  • Contraindications: Children <15 kg, pregnancy, breastfeeding

Treatment Application Guidelines

Proper Application Technique

  • Timing: Apply at bedtime for overnight treatment
  • Preparation: Cool bath before application
  • Coverage:
    • Adults: neck down to toes
    • Infants/elderly: include face and scalp
    • Pay attention to finger webs, under nails
  • Amount: 30g tube sufficient for average adult
  • Reapplication: To hands after washing during treatment

Special Populations

Pregnant and Breastfeeding Women

  • First choice: Permethrin 5% cream
  • Alternative: Sulfur 5-10% ointment
  • Avoid: Ivermectin (pregnancy category C)
  • Safety: Topical treatments preferred

Infants and Children

  • Under 2 months: Sulfur 5% ointment
  • Over 2 months: Permethrin 5% cream
  • Include: Face and scalp in treatment area
  • Mittens: Prevent ingestion from hand-to-mouth

Immunocompromised Patients

  • Combination therapy: Topical plus oral ivermectin
  • Extended treatment: May need multiple cycles
  • Close monitoring: For treatment response
  • Environmental measures: Enhanced decontamination

Crusted Scabies Treatment

Intensive Therapy

  • Combination approach: Topical plus oral treatments
  • Ivermectin: Days 1, 2, 8, 9, 15 (minimum)
  • Topical permethrin: Days 1, 2, 8, 9, 15
  • Keratolytics: Urea or salicylic acid for scale removal
  • Isolation: Until 24 hours after first treatment

Symptomatic Treatment

Antihistamines

  • Oral antihistamines: Diphenhydramine, hydroxyzine
  • Sedating types: Help with sleep disturbance
  • Non-sedating: Loratadine, cetirizine for daytime
  • Duration: May need 2-4 weeks for itch resolution

Topical Treatments for Itch

  • Calamine lotion: Cooling and drying effect
  • Topical corticosteroids: Low-potency for short-term use
  • Menthol or camphor: Cooling sensation
  • Moisturizers: Prevent dry skin

Secondary Infection Treatment

  • Topical antibiotics: Mupirocin for localized infection
  • Oral antibiotics:
    • Cephalexin 250-500 mg qid
    • Clindamycin 150-300 mg qid
    • Azithromycin for resistant cases
  • Duration: 7-10 days typically

Contact Treatment

Who to Treat

  • Household members: All individuals living in same dwelling
  • Sexual partners: Current partners within past month
  • Close contacts: Prolonged skin-to-skin contact
  • Caregivers: Healthcare workers with unprotected contact

Treatment Timing

  • Simultaneous treatment: All contacts on same day
  • Prophylactic treatment: Even if asymptomatic
  • Follow-up: Monitor for symptom development

Environmental Decontamination

Clothing and Bedding

  • Hot water wash: 60°C (140°F) for 10 minutes
  • Hot dryer: High heat for 20 minutes
  • Dry cleaning: Alternative for delicate items
  • Storage: Seal in plastic bags for 72 hours

Other Items

  • Furniture: Vacuum thoroughly
  • Carpets: Vacuum and consider steam cleaning
  • Toys: Wash or store for 72 hours
  • Personal items: Combs, brushes in hot water

Treatment Monitoring

Expected Response

  • Itch improvement: May take 2-4 weeks
  • New lesions: Should stop appearing after 24-48 hours
  • Burrows: Gradually fade over weeks
  • Nodules: May persist for months

Treatment Failure Signs

  • New burrows after 1 week
  • Continued intense itching after 4 weeks
  • New family member symptoms
  • Microscopic evidence of live mites

Prevention

Scabies prevention focuses on avoiding contact with infected individuals, implementing proper hygiene measures, and maintaining vigilance in high-risk settings. Early detection and treatment are crucial for preventing outbreaks.

Primary Prevention

Avoiding Exposure

  • Limit skin contact: Avoid prolonged skin-to-skin contact with infected individuals
  • Sexual health: Practice safe sexual behaviors, know partner's health status
  • Recognize symptoms: Be aware of scabies signs in household members
  • Prompt treatment: Seek medical care for suspicious symptoms

Institutional Prevention

Healthcare Facilities

  • Isolation protocols:
    • Contact precautions for suspected/confirmed cases
    • Private room until 24 hours after treatment
    • Gown and gloves for staff contact
    • Proper hand hygiene
  • Screening programs:
    • Regular skin assessments for residents/patients
    • Staff education on recognition
    • Outbreak investigation protocols
  • Environmental measures:
    • Proper laundry procedures
    • Room cleaning protocols
    • Shared equipment decontamination

Schools and Childcare

  • Education: Staff training on scabies recognition
  • Notification: Inform parents of cases while maintaining privacy
  • Exclusion policy: Temporary exclusion until treatment completed
  • Environmental cleaning: Enhanced cleaning of shared items

Personal Hygiene Measures

General Hygiene

  • Regular bathing: Daily washing with soap and water
  • Clean clothing: Daily change of clothes and underwear
  • Nail care: Keep fingernails short and clean
  • Avoid sharing: Personal items like clothing, towels, bedding

Laundry Practices

  • Hot water washing: Use hottest water safe for fabric
  • High heat drying: Machine dry on high heat when possible
  • Regular washing: Frequent laundering of bedding and clothes
  • Separate washing: Don't mix potentially contaminated items

Household Prevention

During Active Infestation

  • Simultaneous treatment: Treat all household members at once
  • Environmental decontamination: Clean all potentially contaminated items
  • Isolation measures: Limit visitors until treatment effective
  • Follow-up care: Monitor all family members for symptoms

High-Risk Households

  • Immunocompromised members: Extra vigilance and prompt treatment
  • Multiple children: Regular skin checks and hygiene education
  • Overcrowded conditions: Maximize space and ventilation
  • Limited resources: Prioritize essential prevention measures

Travel and Community Prevention

Travel Precautions

  • Accommodation choice: Research cleanliness standards
  • Bedding inspection: Check for signs of infestation
  • Personal items: Avoid sharing with fellow travelers
  • Post-travel monitoring: Watch for symptoms after return

Community Outbreaks

  • Reporting: Notify health authorities of suspected outbreaks
  • Communication: Share information with affected communities
  • Coordination: Organize simultaneous treatment efforts
  • Resources: Ensure access to treatment for all affected

Occupational Prevention

Healthcare Workers

  • Personal protective equipment: Gloves and gowns when indicated
  • Hand hygiene: Thorough handwashing after patient contact
  • Skin monitoring: Regular self-examination for symptoms
  • Education: Stay updated on prevention protocols

Childcare Workers

  • Symptom awareness: Know what to look for in children
  • Reporting procedures: Prompt notification of suspected cases
  • Hygiene practices: Good hand hygiene and general cleanliness
  • Environmental care: Regular cleaning of toys and surfaces

Special Populations

Immunocompromised Individuals

  • Enhanced vigilance: More frequent skin examinations
  • Prompt treatment: Immediate medical attention for symptoms
  • Caregiver education: Train caregivers on recognition and prevention
  • Environmental control: Stricter hygiene measures

Elderly Residents

  • Regular assessments: Routine skin examinations
  • Caregiver training: Education on scabies recognition
  • Prompt intervention: Quick response to suspected cases
  • Communication: Clear reporting systems

Education and Awareness

Public Education

  • Symptom recognition: Community education on scabies signs
  • Transmission understanding: How scabies spreads
  • Treatment importance: Need for prompt medical care
  • Stigma reduction: Education that anyone can get scabies

Professional Education

  • Healthcare providers: Diagnosis and treatment protocols
  • School personnel: Recognition and response procedures
  • Social workers: Identification in at-risk populations
  • Public health officials: Outbreak investigation and control

When to See a Doctor

Seek immediate medical attention for:

  • Signs of severe secondary bacterial infection (fever, red streaking, spreading cellulitis)
  • Thick, crusted lesions covering large areas (crusted scabies)
  • Severe symptoms in immunocompromised individuals
  • Difficulty breathing or signs of allergic reaction to treatment
  • Persistent high fever with skin symptoms

Schedule urgent care for:

  • Intense itching of skin that worsens at night
  • Characteristic skin rash in typical locations
  • Multiple family members with similar symptoms
  • Abnormal appearing skin with burrow-like lesions
  • Known exposure to confirmed scabies case
  • Institutional outbreak situation

Follow-up care needed for:

  • Persistent itching 4 weeks after treatment
  • New lesions appearing after treatment
  • Signs of treatment failure or reinfection
  • Development of nodular lesions
  • Skin swelling or signs of secondary infection
  • Need for retreatment or alternative therapy

Prevention consultation for:

  • High-risk living situations (institutional settings)
  • Immunocompromised status with exposure risk
  • Healthcare workers with occupational exposure
  • Travel to areas with high scabies prevalence
  • Questions about household contact treatment

Related Conditions

References

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  2. Romani L, Steer AC, Whitfeld MJ, Kaldor JM. Prevalence of scabies and impetigo worldwide: a systematic review. Lancet Infect Dis. 2015;15(8):960-967.
  3. Strong M, Johnstone PW. Interventions for treating scabies. Cochrane Database Syst Rev. 2007;(3):CD000320.
  4. Salavastru CM, Chosidow O, Boffa MJ, et al. European guideline for the management of scabies. J Eur Acad Dermatol Venereol. 2017;31(8):1248-1253.
  5. Walton SF, Currie BJ. Problems in diagnosing scabies, a global disease in human and animal populations. Clin Microbiol Rev. 2007;20(2):268-279.