Scabies

Contagious parasitic skin infestation caused by Sarcoptes scabiei

Scabies
Synonyms	Seven-year itch; human scabies; sarcoptic mange in humans
Pronounce	N/A
Specialty	N/A
Symptoms	Intense itching, especially at night; pimple-like rash; burrows; excoriations; nodules in some patients
Complications	Impetigo, cellulitis, abscess, sepsis, post-streptococcal glomerulonephritis, rheumatic heart disease in high-burden settings, sleep disturbance, crusted scabies
Onset	Usually 2–6 weeks after first infestation; 1–4 days after reinfestation
Duration	Persists until treated; itching may continue for 2–4 weeks after successful treatment
Types	N/A
Causes	Infestation with the mite Sarcoptes scabiei var. hominis
Risks	Close skin-to-skin contact, household exposure, sexual contact, crowded living conditions, childcare facilities, nursing homes, prisons, shelters, refugee settings, immunosuppression, older age, neurologic disability, limited access to diagnosis or treatment
Diagnosis	Clinical examination; identification of burrows; dermoscopy; skin scraping, adhesive tape test, or microscopy when needed
Differential diagnosis	Atopic dermatitis, contact dermatitis, eczema, pediculosis, bed bug bites, papular urticaria, impetigo, folliculitis, dermatitis herpetiformis, seborrheic dermatitis, drug eruption
Prevention	Early diagnosis, simultaneous treatment of close contacts, avoidance of prolonged skin-to-skin contact until treated, laundering or isolating recently used clothing and bedding, outbreak control in institutions
Treatment	Topical scabicides, oral ivermectin in selected cases, treatment of household and sexual contacts, environmental decontamination, treatment of secondary bacterial infection when present
Medication	Permethrin 5% cream; ivermectin; benzyl benzoate; sulfur ointment; crotamiton; spinosad topical suspension; lindane only when safer options cannot be used
Prognosis	Excellent with correct treatment and contact management; recurrence is common if contacts are untreated or treatment is applied incorrectly
Frequency	Common worldwide; hundreds of millions of cases are estimated globally each year
Deaths	Rare in classic scabies; crusted scabies and secondary bacterial infection can cause severe disease and death in vulnerable patients

Scabies is a contagious parasitic skin infestation caused by the human itch mite Sarcoptes scabiei var. hominis. The female mite burrows into the outer layer of the skin, where it lays eggs and triggers a delayed hypersensitivity reaction. The characteristic clinical features are intense itching, often worse at night, and a papular or vesicular rash with thin burrow tracks in typical body locations.

Scabies affects people of all ages and socioeconomic groups. It spreads mainly through prolonged direct skin-to-skin contact, including household contact and sexual contact. Transmission by clothing, bedding, or towels is less common in ordinary scabies but becomes more important in crusted scabies, where the number of mites may be extremely high. Scabies is especially important in crowded settings such as childcare centers, long-term care facilities, shelters, prisons, refugee camps, and institutions.

Although classic scabies is usually not life-threatening, it can cause severe itching, sleep disturbance, social stigma, and secondary bacterial infection. Bacterial complications may include impetigo, cellulitis, abscess, sepsis, and, in some settings, post-streptococcal kidney and heart complications. The World Health Organization recognizes scabies as a neglected tropical disease and notes that scabies is frequently complicated by bacterial skin infection, which may lead to invasive infection and kidney or rheumatic heart disease in high-burden settings.

File:Scabies Thorax.JPG

Scabies lesions on the thorax

File:Scabies Nodules hand.JPG

Nodular scabies lesions on the hand

Scabies burrow

Cause

Scabies is caused by infestation with Sarcoptes scabiei var. hominis, a microscopic eight-legged mite. The mite lives in the outermost layer of the skin, the stratum corneum. Female mites burrow into the skin and lay eggs. Larvae hatch, mature, and continue the life cycle on the host.

The itching and rash are caused mainly by the body's immune reaction to mites, eggs, saliva, and fecal material rather than by mechanical damage alone.

Transmission

Scabies usually spreads through prolonged close skin contact. Brief contact, such as a handshake or casual touch, is less likely to spread classic scabies, but transmission risk increases with longer contact and in crowded settings.

Common routes of transmission include:

• Household contact
• Sexual contact
• Close caregiving contact
• Skin-to-skin contact among children
• Contact in nursing homes or long-term care facilities
• Contact in shelters, prisons, or crowded living settings
• Shared bedding or clothing, especially in crusted scabies

Mites generally do not survive long away from human skin, but recently used bedding, clothing, and towels can contribute to reinfestation if not handled properly.

Incubation period

The incubation period depends on whether the person has been exposed before:

Exposure type	Typical onset of symptoms
First infestation	Usually 2–6 weeks after exposure
Reinfestation	Often within 1–4 days because of immune sensitization

A person can spread scabies before symptoms appear, especially during the first infestation.

Signs and symptoms

The most common symptom is intense itching, often worse at night. The rash is usually composed of small erythematous papules, vesicles, excoriations, crusts, or nodules. Thin, wavy, gray-white or skin-colored burrows may be seen, especially in classic locations.

Common symptoms and signs include:

• Severe itching
• Nighttime worsening of itching
• Small red bumps or papules
• Vesicles or pustules
• Thin burrow tracks
• Scratch marks and excoriations
• Crusting or scaling
• Nodules, especially in the genital, axillary, or groin areas
• Secondary bacterial infection

Common body sites

In older children and adults, scabies commonly affects:

• Web spaces between the fingers
• Wrists
• Elbows
• Armpits
• Waistline
• Umbilicus
• Buttocks
• Genitals
• Areolae
• Inner thighs
• Ankles and feet

In infants, young children, older adults, and immunocompromised patients, scabies may also involve the scalp, face, neck, palms, and soles.

Types of scabies

Classic scabies

Classic scabies is the usual form. The mite burden is often low, sometimes only 10–15 adult female mites, but the immune reaction produces intense itching and rash.

Nodular scabies

Nodular scabies causes persistent itchy nodules, often in the groin, axillae, or genital region. Nodules may persist after mites are eradicated because they reflect an inflammatory hypersensitivity response.

Crusted scabies

Crusted scabies, also called Norwegian scabies, is a severe and highly contagious form characterized by thick crusts, scaling, fissures, and a very high mite burden. It occurs more often in people with impaired immune responses, advanced age, neurologic impairment, institutionalization, or inability to scratch effectively.

Risk factors for crusted scabies include:

• HIV/AIDS
• Immunosuppression
• Organ transplant medications
• Leukemia or lymphoma
• Advanced age
• Dementia or neurologic disability
• Down syndrome
• Long-term care residence
• Severe malnutrition

Crusted scabies can cause institutional outbreaks and often requires combination therapy with topical scabicides, repeated oral ivermectin, keratolytic treatment, contact precautions, and public health control measures.

Diagnosis

Scabies is often diagnosed clinically from the history, distribution of itching, close-contact exposure, and typical lesions. Diagnosis is more likely when multiple household members or close contacts have itching.

Diagnostic methods may include:

• Clinical skin examination
• Identification of burrows
• Dermoscopy
• Skin scraping with microscopy
• Adhesive tape test
• Needle extraction of mite material
• Ink test to highlight burrows
• Examination for mites, eggs, or scybala

A negative skin scraping does not rule out scabies, because mites may be few and hard to capture in classic disease.

Differential diagnosis

Conditions that may resemble scabies include:

• Atopic dermatitis
• Contact dermatitis
• Eczema
• Pediculosis
• Bed bug bites
• Flea bites
• Papular urticaria
• Folliculitis
• Impetigo
• Dermatitis herpetiformis
• Seborrheic dermatitis
• Drug eruption
• Psoriasis
• Prurigo nodularis
• Tinea corporis

Treatment overview

Scabies treatment has four goals:

1. Kill mites and eggs.
2. Relieve itching and inflammation.
3. Treat all close contacts at the same time.
4. Prevent reinfestation from untreated contacts or contaminated items.

Prescription scabicides are usually required. The CDC notes that scabicides are medications that kill scabies mites; permethrin cream and oral ivermectin are commonly used options, and oral ivermectin is not FDA-approved for scabies in the United States but may be prescribed off-label.

Medications

Medication	Usual role	Notes
Permethrin 5% cream	First-line topical treatment in many guidelines	Applied to the body as directed and washed off after the recommended time; repeat treatment may be needed.
Ivermectin	Oral therapy for selected cases, outbreaks, difficult application, or crusted scabies	Often given as two 200 mcg/kg doses 7–14 days apart for classic scabies when used; safety is not established in pregnancy or children under 15 kg in CDC guidance.
Benzyl benzoate	Topical scabicide used in many countries	Can irritate skin; instructions vary by formulation and country.
Sulfur ointment	Alternative topical option	Sometimes used in infants, pregnancy, or situations where other agents are unsuitable, depending on clinician guidance.
Crotamiton	Alternative topical option	Less commonly used; treatment failures have been reported.
Spinosad topical suspension	Prescription topical option in some settings	FDA-approved in the United States for scabies in patients 4 years and older.
Lindane	Second-line or last-line option	Not preferred because of neurotoxicity risk; should not be used in infants, pregnant or breastfeeding people, older adults, people with extensive dermatitis, or people weighing less than 50 kg.

How to apply permethrin cream

General instructions may vary by prescription label and local guideline, but typical steps include:

1. Apply at bedtime to clean, dry skin.
2. Cover the entire body surface from the neck down in adults, including under nails, between fingers and toes, soles, groin, buttocks, and skin folds.
3. In infants, young children, older adults, and immunocompromised patients, clinicians may instruct application to the scalp, hairline, neck, temples, and forehead while avoiding the eyes and mouth.
4. Leave on for the prescribed time, often 8–14 hours.
5. Wash off thoroughly.
6. Put on clean clothes.
7. Repeat treatment if directed, commonly after 7–14 days.

Do not use scabies medications in the eyes, mouth, or mucous membranes unless specifically directed by a clinician.

Oral ivermectin

When oral ivermectin is used for classic scabies, two doses are commonly used because ivermectin has limited effect on eggs. CDC clinical guidance describes two doses of oral ivermectin 200 mcg/kg/dose taken with food, 7–14 days apart, for classic scabies when this therapy is chosen.

Oral ivermectin should be used under medical supervision, especially in:

• Pregnant people
• Breastfeeding people
• Children weighing less than 15 kg
• People with severe liver disease
• People taking interacting medications
• Patients with crusted scabies
• Institutional outbreaks

Treating contacts

All close contacts should be treated at the same time, even if they do not yet have symptoms. This includes household members, sexual partners, and close caregiving contacts. Treating only the symptomatic person is a common reason for recurrence.

Environmental control

Environmental steps help prevent reinfestation:

• Wash clothing, towels, and bedding used during the previous several days.
• Use hot water and high-heat drying when fabric allows.
• Dry-clean items that cannot be washed.
• Seal unwashable items in a plastic bag for several days, according to local guidance.
• Avoid sharing clothing, towels, and bedding until treatment is completed.
• Vacuum upholstered furniture and mattresses in institutional or outbreak settings.

Routine pesticide spraying of rooms is usually unnecessary and may be harmful.

Itching after treatment

Itching can continue for 2–4 weeks after successful treatment because the immune system continues to react to mite proteins and debris. This is called post-scabies itch and does not always mean treatment failure.

Symptom relief may include:

• Oral antihistamines for sleep-disrupting itch
• Mild topical corticosteroids for inflammation
• Emollients and skin barrier care
• Treatment of secondary infection if present
• Re-evaluation if new burrows or new lesions continue to appear

Persistent itching beyond several weeks, new burrows, or ongoing itching in untreated contacts may suggest reinfestation or treatment failure.

Complications

Scabies complications include:

• Severe itching and sleep loss
• Excoriations
• Impetigo
• Cellulitis
• Skin abscess
• Sepsis
• Post-streptococcal glomerulonephritis
• Rheumatic fever and rheumatic heart disease in high-burden settings
• Crusted scabies
• Institutional outbreaks
• Anxiety, stigma, and reduced quality of life

WHO notes that scabies-associated impetigo can be complicated by abscesses, sepsis, invasive bacterial infection, kidney disease, and rheumatic heart disease, particularly where scabies and streptococcal skin infection are common.

Scabies in special populations

Infants and young children

Infants may have more widespread disease involving the scalp, face, palms, and soles. Treatment should be directed by a clinician because medication choice and application differ by age and weight.

Pregnancy and breastfeeding

Pregnant or breastfeeding patients should consult a clinician before treatment. Permethrin is often used, but medication choice should be individualized. The safety of oral ivermectin in pregnancy has not been established in CDC guidance.

Older adults and long-term care residents

Older adults may have atypical symptoms and may be at greater risk of delayed diagnosis, institutional spread, and crusted scabies. Long-term care outbreaks require coordinated diagnosis, treatment, environmental measures, and staff/resident contact management.

Immunocompromised patients

Immunocompromised patients are at increased risk for crusted scabies. They may have extensive scaling with less itching than expected and require urgent specialist care.

Outbreak control

Outbreaks may occur in hospitals, nursing homes, prisons, childcare centers, shelters, and other institutions. Control measures include:

• Early recognition of cases
• Confirming diagnosis when possible
• Treating affected persons and exposed contacts simultaneously
• Contact precautions for crusted scabies
• Staff education
• Laundry and bedding control
• Screening of symptomatic contacts
• Repeat treatment according to protocol
• Public health involvement when needed

Prevention

Scabies prevention includes:

• Avoiding prolonged skin-to-skin contact with untreated infected persons
• Treating household and sexual contacts at the same time
• Avoiding shared clothing, towels, and bedding during active infestation
• Washing or isolating recently used bedding and clothing
• Rapid diagnosis and treatment in institutions
• Education about correct medication application
• Follow-up when symptoms persist or recur

Prognosis

The prognosis for classic scabies is excellent when treatment is applied correctly and close contacts are treated. Symptoms usually improve gradually after treatment, but itching may persist for several weeks. Recurrence is common when contacts are not treated, treatment is not repeated when needed, or crusted scabies is missed.

Crusted scabies has a more serious prognosis because of high mite burden, risk of outbreaks, secondary infection, sepsis, and underlying illness.

When to seek medical care

Medical care is recommended when:

• A person has intense nighttime itching with a spreading rash
• Several household members are itchy
• A child, older adult, pregnant person, or immunocompromised person is affected
• There are signs of bacterial infection such as pus, increasing redness, warmth, swelling, pain, fever, or red streaks
• Thick crusting or widespread scaling is present
• Symptoms persist after correct treatment
• Scabies occurs in a nursing home, shelter, prison, hospital, or childcare setting

Public health importance

Scabies is common worldwide and disproportionately affects people in crowded or resource-limited settings. The burden is highest in many tropical regions and in communities with limited access to timely diagnosis, treatment, clean clothing, washing facilities, and coordinated contact treatment.

Scabies control can reduce itching, school and work disruption, secondary bacterial infections, and severe complications related to bacterial skin disease.

Key points

• Scabies is caused by the mite Sarcoptes scabiei var. hominis.
• It spreads mainly through prolonged skin-to-skin contact.
• Itching is often severe and worse at night.
• Burrows are highly suggestive when present.
• Treat close contacts at the same time.
• Permethrin 5% cream is a common first-line treatment.
• Oral ivermectin is used in selected cases and outbreaks, but is not FDA-approved for scabies in the United States.
• Crusted scabies is highly contagious and requires urgent medical and public health management.
• Itching may continue for several weeks after mites are killed.

See also

• Sarcoptes scabiei
• Parasitic skin disease
• Skin infection
• Pruritus
• Impetigo
• Cellulitis
• Pediculosis
• Bed bug
• Dermatology
• Infectious disease
• Neglected tropical disease
• Ivermectin
• Permethrin

External links

• CDC - Scabies
• WHO - Scabies
• Scabies - NCBI Bookshelf