Scabies

How scabies works

The female mite, smaller than a pinhead, burrows into the outer skin and lays 2 to 3 eggs a day. Eggs hatch in a few days and mature into adults within about 2 weeks. Most people have only 10 to 15 mites. The itching and rash are mostly an allergic reaction to the mites, their eggs and their waste.

• First infection: symptoms take 2 to 6 weeks to appear, but you can spread scabies during this time.
• Reinfection: symptoms start within 1 to 4 days, because the immune system is already primed.

Off the body, mites usually survive only 2 to 3 days.

Symptoms

• intense itching, often worse at night or after a hot shower
• a rash of small red bumps, blisters or pimple-like spots
• burrows: thin, gray or skin-colored wavy lines a few millimeters long, sometimes with a tiny dot at one end
• sores from scratching, which can become infected

Where it appears

Adults and older children:

• between the fingers and the sides of the fingers
• wrists and inner elbows
• armpits
• waistline and belly button
• buttocks
• around the nipples
• penis and scrotum, where firm, itchy bumps (nodules) are common

The head and face are usually spared in adults.

Babies and young children: the rash can be widespread, including the head, face, neck, palms and soles.

Crusted (Norwegian) scabies

A severe form in which a person carries thousands to millions of mites. It causes thick, gray crusts and scales, often on the hands, feet, elbows and scalp, and may itch little. It occurs in people with weakened immunity, older adults in care homes, and people with disabilities or nerve conditions. It is extremely contagious and can cause outbreaks in institutions. It needs combined treatment with oral ivermectin and topical medicine.

How scabies spreads

• prolonged skin-to-skin contact: living in the same household, sharing a bed, caring for someone, sexual contact
• less commonly, sharing bedding, towels or clothing, especially with crusted scabies
• outbreaks are common in nursing homes, childcare settings, prisons and crowded housing

A quick handshake or hug is unlikely to spread typical scabies. Scabies is not a sign of poor hygiene. Animal scabies (mange) can cause temporary itching in people but does not survive or reproduce on humans.

Scabies vs other itchy rashes

Diagnosis

A doctor usually diagnoses scabies from the typical rash and itch, especially when household members are also itchy. Confirmation can come from:

• dermoscopy: a magnifying light that can show the mite at the end of a burrow ("delta wing" sign)
• skin scraping: examined under a microscope for mites, eggs or mite feces
• ink test: ink rubbed over a burrow and wiped off leaves a dark line

A negative scraping does not rule out scabies because there are so few mites.

Treatment

Medicines

• Permethrin 5% cream: the most common treatment. Apply to clean, dry, cool skin from the neck down (including the scalp and face for babies and older adults, as directed), paying attention to finger webs, under nails, genitals and between the buttocks. Leave on for 8 to 14 hours, usually overnight, then wash off. Repeat in about 7 to 14 days.
• Oral ivermectin: two doses about a week apart. Often used for crusted scabies, outbreaks, or when creams are impractical. Not usually used in young children under about 15 kg or in pregnancy.
• Other options: spinosad, benzyl benzoate, sulfur ointment (often used for young babies and pregnancy) and others as directed.

Treat everyone at once

Household members, sexual partners and close contacts should be treated at the same time, even without symptoms, to prevent ping-pong reinfection.

Cleaning

• wash clothing, towels and bedding used in the 3 days before treatment in hot water, at least 50 °C (122 °F), and dry on high heat
• seal items that cannot be washed in a plastic bag for at least 72 hours
• vacuum furniture and carpets
• fumigating the home is not needed

Itch relief

• itching often lasts 2 to 4 weeks after successful treatment as the skin heals
• moisturizers, cool compresses, oral antihistamines and mild steroid creams can help
• see a doctor if itching lasts beyond 4 weeks or new burrows appear

Children and adults can usually return to school or work the day after the first treatment.

Complications

• secondary bacterial infection such as impetigo or cellulitis, from scratching
• in some parts of the world, untreated scabies infections are linked to kidney and heart complications from streptococcal bacteria
• sleep loss and distress from itching

Frequently asked questions

What does a scabies rash look like?

It looks like small red bumps or pimples, sometimes with tiny blisters, and thin, wavy lines (burrows) a few millimeters long. It is often between the fingers, on the wrists, elbows, waist, buttocks and genitals. The itch is intense and worse at night.

How do you get scabies?

Scabies spreads mainly through prolonged skin-to-skin contact, such as sharing a bed, living together or sexual contact. Less often it spreads through shared bedding or clothing. It is not caused by poor hygiene, and you cannot catch human scabies from pets.

How long is scabies contagious?

Scabies is contagious from the time you are infested, even before symptoms appear, until you have been treated. Most people are no longer contagious about 24 hours after the first treatment, though crusted scabies takes longer.

Why do I still itch after scabies treatment?

Itching can continue for 2 to 4 weeks after successful treatment because the skin is still reacting to dead mites and their debris. This is normal. If new burrows appear or itching lasts longer than 4 weeks, see a doctor, as retreatment may be needed.