Scabies: Symptoms, Treatment & How It Spreads

What Is Scabies and What Causes It?

Scabies is a parasitic skin infestation caused by the microscopic mite Sarcoptes scabiei var. hominis. The female mite burrows into the top layer of skin to lay eggs, causing intense itching from an allergic reaction. Approximately 200 million people worldwide are affected at any given time.

Scabies is caused by a tiny eight-legged mite that is barely visible to the naked eye, measuring only 0.3-0.4 millimeters. The female scabies mite burrows into the outermost layer of skin (stratum corneum) where she creates tunnels and lays 2-3 eggs per day for her 4-6 week lifespan. These burrows appear as thin, wavy, grayish-white lines on the skin surface, typically about 1 centimeter long.

The mites cannot survive more than 48-72 hours away from human skin, as they require the warmth and environment of the human body to complete their life cycle. When mites are on the skin surface, they can crawl at a rate of about 2.5 centimeters per minute on warm skin, which is why prolonged skin contact is necessary for transmission. The entire life cycle from egg to adult takes approximately 10-17 days.

Most people with scabies have only 10-15 mites on their body at any given time, despite the intense symptoms. The severe itching is not caused by the mites burrowing but rather by the body's allergic reaction to the mites, their eggs, and their fecal matter. This immune response takes time to develop, which explains the delay between infection and the onset of symptoms.

Human scabies vs. animal scabies

The human scabies mite (Sarcoptes scabiei var. hominis) is different from mites that infest dogs, cats, and foxes. When animal scabies mites come into contact with human skin, they may cause temporary itching and small bites, but they cannot reproduce or survive long-term on humans. These animal mite infestations typically resolve on their own within a few weeks without treatment, though the affected pet should be treated by a veterinarian.

What Are the Symptoms of Scabies?

The main symptoms of scabies include intense itching that worsens at night, thin burrow tracks in the skin, small blisters and red bumps, and scratch marks from itching. Symptoms typically appear 2-6 weeks after first infection or within 1-4 days if you've had scabies before.

The hallmark symptom of scabies is intense, persistent itching that characteristically becomes worse at night and when the body is warm, such as after a hot bath. The itching is caused by the immune system's allergic reaction to proteins in the mite's body and feces, not from the actual burrowing sensation. Many patients describe the itching as so severe that it disrupts sleep and daily activities.

The itching can occur anywhere on the body, including areas where no mites are present, because it is an immune-mediated response. This widespread itching often leads to extensive scratching, which can cause secondary skin damage including scratch marks, scabs, and even bacterial infections. The psychological impact of constant itching should not be underestimated - it can lead to anxiety, irritability, and significant reduction in quality of life.

Skin changes and rash patterns

The visible signs of scabies include several characteristic skin changes. Burrow tracks appear as thin, wavy, slightly raised grayish-white or skin-colored lines, usually 2-15 mm in length. At the end of each burrow, you may see a tiny dark spot which is the mite itself. Small fluid-filled blisters (vesicles) and red papules often appear near the burrows.

The rash distribution follows predictable patterns in adults, typically affecting the spaces between fingers, the inner wrists, elbows, armpits, waistline, buttocks, and genitals (especially in men). The palms, soles, and face are usually spared in adults but may be affected in infants and elderly individuals. The rash may also include small red bumps, hives-like reactions, and excoriations from scratching.

Delayed symptom onset

One of the most important facts about scabies is that symptoms typically take 2-6 weeks to appear after the initial infection if you have never had scabies before. This delay occurs because the itching is caused by an allergic sensitization to the mites, which takes time to develop. During this asymptomatic period, an infected person can unknowingly spread scabies to others.

If you have previously had scabies, your immune system already recognizes the mite antigens, and symptoms can appear within 1-4 days of re-infection. This is why people sometimes notice symptoms much faster upon repeat exposure.

Crusted (Norwegian) scabies

Crusted scabies, previously called Norwegian scabies, is a severe and highly contagious form that primarily affects people with weakened immune systems, the elderly in nursing homes, or those with neurological conditions that reduce the sensation of itching. Unlike typical scabies where a person has 10-15 mites, someone with crusted scabies can harbor thousands to millions of mites.

Crusted scabies presents with thick, warty crusts on the skin, especially on the hands, feet, and under the nails. Despite the massive mite infestation, itching may be minimal or absent due to a reduced immune response. This form is extremely contagious and requires specialized treatment and infection control measures.

How Does Scabies Spread?

Scabies spreads primarily through prolonged direct skin-to-skin contact lasting several minutes. Common transmission scenarios include sleeping in the same bed, holding hands for extended periods, and sexual contact. Brief casual contact like handshakes rarely transmits scabies. Spread through clothing or bedding is uncommon with typical scabies.

The scabies mite cannot jump or fly - it can only crawl. For transmission to occur, mites must crawl from one person's skin to another's, which requires sustained close physical contact. Studies have shown that brief contact like handshakes, hugs, or sitting next to someone typically does not provide enough time for mites to transfer. The commonly cited guideline is that about 15-20 minutes of continuous skin-to-skin contact is needed for transmission.

The most common transmission scenarios include sleeping in the same bed with an infected person, prolonged hand-holding (such as a parent comforting a child), sexual contact, and caregiving activities that involve extended physical contact. Household transmission is common because family members naturally have frequent close contact.

Transmission through objects

With typical scabies (10-15 mites), transmission through objects like clothing, towels, and bedding is possible but uncommon. Mites can survive off human skin for 24-72 hours under favorable conditions, but they become weakened and less likely to infect during this time. The risk of transmission through shared items is higher in crowded conditions or when items are shared immediately after use by an infected person.

However, with crusted scabies, the massive number of mites means that transmission through environmental contamination is much more likely. Patients with crusted scabies can shed large numbers of mites into their environment, making indirect transmission a significant concern.

Infectivity period

A person with scabies is contagious from the time of infestation until treatment is complete - this includes the 2-6 week asymptomatic period before symptoms appear. This is why all close contacts should be treated simultaneously even if they have no symptoms, as they may be in the early stages of infestation.

When Should You See a Doctor for Scabies?

See a doctor if you have persistent itching and suspect scabies, if itching continues 3-4 weeks after treatment, or if symptoms return after initial improvement. If you've had confirmed close contact with someone diagnosed with scabies, you should be treated even without symptoms.

It is important to get a proper diagnosis before treating scabies because many other skin conditions can cause similar symptoms. Conditions that may mimic scabies include eczema, contact dermatitis, insect bites, folliculitis, and various other forms of dermatitis. Treating for scabies when you have another condition will not resolve your symptoms and may delay proper treatment.

A healthcare provider can diagnose scabies by examining the skin, looking for characteristic burrows, and potentially performing a skin scraping to identify mites, eggs, or fecal matter under a microscope. In some cases, a special tool called a dermatoscope may be used to visualize mites in their burrows.

Situations requiring medical attention

• New persistent itching: If you develop itching that worsens at night and doesn't respond to usual remedies, especially if someone in your household has been diagnosed with scabies
• Signs of infection: If scratched areas become red, swollen, warm, painful, or develop pus - this may indicate a secondary bacterial infection requiring antibiotics
• Symptoms after treatment: If itching remains severe or worsens more than 3-4 weeks after completing treatment
• Recurring symptoms: If you improve after treatment but symptoms return, indicating possible reinfection
• Severe symptoms: If symptoms are very severe or you have thick, crusty skin that could indicate crusted scabies

If you have been in close physical contact with someone who has confirmed scabies, you should be treated at the same time as them, even if you have no symptoms. This is because you may be in the asymptomatic incubation period, and simultaneous treatment prevents the ping-pong effect of passing the infection back and forth.

How Is Scabies Diagnosed?

Scabies is diagnosed through skin examination by a healthcare provider looking for characteristic burrows and rash patterns. Definitive diagnosis involves skin scraping to identify mites, eggs, or fecal matter under a microscope. Dermoscopy can also visualize mites in burrows without invasive procedures.

The diagnosis of scabies begins with a careful medical history, including questions about the nature and timing of symptoms, whether itching worsens at night, whether household members or close contacts have similar symptoms, and any previous scabies infections. The characteristic pattern of nocturnal itching that affects multiple household members strongly suggests scabies.

Physical examination involves careful inspection of the skin, particularly in the common locations for scabies burrows: between the fingers, on the wrists, elbows, armpits, waist, buttocks, and genitals. The examiner looks for the characteristic thin, wavy burrow tracks, small papules, vesicles, and excoriations from scratching.

Microscopic examination

The definitive diagnosis of scabies requires identification of the mite, eggs, or fecal pellets (scybala). This is typically done by scraping the skin at the end of a burrow with a scalpel blade or needle to collect material, which is then examined under a microscope. A positive finding of any of these elements confirms the diagnosis.

However, because the number of mites in typical scabies is low (10-15), skin scrapings are often negative even in confirmed cases. A negative scraping does not rule out scabies, and treatment decisions are often made based on clinical presentation and history.

Dermoscopy

Dermoscopy is a non-invasive technique that uses a handheld magnifying device with a light source to examine the skin. With dermoscopy, the scabies mite can often be visualized as a small dark triangular structure at the end of a burrow, sometimes described as looking like a "jet plane with contrail" or "delta wing sign." This technique is increasingly used as it allows rapid diagnosis without the need for skin scraping.

How Is Scabies Treated?

Scabies is treated with topical medications applied to the entire body from the neck down (including head in infants). Permethrin 5% cream is the first-line treatment, left on for 8-14 hours. Treatment is repeated after 7-10 days. All household members and close contacts must be treated simultaneously, even without symptoms.

The treatment of scabies involves killing the mites and their eggs with prescription medications, treating all household members and close contacts at the same time, and decontaminating the environment. Treatment failure is common when these steps are not followed completely, leading to reinfection and ongoing transmission.

First-line treatment: Permethrin cream

Permethrin 5% cream is considered the first-line treatment for scabies worldwide due to its high efficacy (89-98% cure rate) and good safety profile. The cream should be applied to cool, dry skin - not immediately after a hot bath, as enhanced absorption can increase side effects. Apply to the entire body from the neck down, with special attention to areas between fingers, under fingernails, wrists, elbows, armpits, waist, buttocks, and genitals.

Leave the permethrin on for 8-14 hours (usually overnight), then wash it off in the shower. If you wash your hands during the treatment period, reapply permethrin to the hands. A second treatment should be applied 7-10 days later to kill any mites that may have hatched from eggs after the first treatment.

Alternative treatments

Benzyl benzoate: This older treatment is available in many countries and is applied in a similar fashion to permethrin. Some formulations combine benzyl benzoate with disulfiram. It may be more irritating to the skin than permethrin.

Ivermectin: Oral ivermectin is an effective alternative, particularly useful for crusted scabies, outbreaks in institutions, or when topical treatment is impractical. The standard dose is 200 micrograms per kilogram of body weight, taken as a single dose and repeated after 1-2 weeks. Ivermectin is not approved for use in pregnant women or children under 15 kg.

Sulfur preparations: Precipitated sulfur (5-10%) in petrolatum is a traditional treatment that is safe for use in infants and pregnant women. It must be applied for three consecutive nights and can have an unpleasant odor and feel greasy.

Special populations

For infants under 2 months and pregnant or breastfeeding women, permethrin is considered the safest option, though the treatment should cover the entire body including the head and face (avoiding eyes and mouth) in young infants. Sulfur preparations are also safe in these populations.

In infants, the head, face, and scalp should be included in treatment because scabies commonly affects these areas in young children. This is different from adult treatment where these areas are typically spared.

Environmental decontamination

On the day of treatment, you should:

• Change into fresh clothing after applying the treatment
• Wash all bedding, towels, and recently worn clothing in hot water (at least 60°C/140°F) and dry on high heat
• Items that cannot be washed should be sealed in a plastic bag for 72 hours or left unused - mites will die without human contact
• Vacuum furniture and carpets, then discard the vacuum bag
• There is no need to fumigate or use insecticide sprays

What Happens After Scabies Treatment?

Itching commonly continues for 2-4 weeks after successful treatment due to the ongoing allergic reaction to dead mites. Use hydrocortisone cream to relieve itching. If itching persists beyond 4 weeks or worsens, consult a doctor as retreatment may be needed.

Many people are surprised and concerned that itching continues after treatment, but this is completely normal and expected. The itching is caused by an allergic reaction to mite proteins, and dead mites, eggs, and fecal matter remain in the skin until the outer layer naturally sheds - a process that takes several weeks. The immune reaction continues until these antigens are eliminated.

During this post-treatment period, hydrocortisone cream (available over-the-counter) can be applied to itchy areas to reduce inflammation and provide relief. Oral antihistamines may also help with sleep if nighttime itching is severe. Cool baths with colloidal oatmeal can soothe irritated skin.

Signs of treatment failure

If symptoms are not improving or are getting worse after 2-3 weeks, or if you notice new burrows appearing, this may indicate treatment failure. Possible reasons for treatment failure include:

• Incomplete application of the medication (missing areas like under nails, between toes)
• Not treating all household members and close contacts
• Not completing the second treatment after 7-10 days
• Reinfection from an untreated contact
• Resistance to the medication (rare but increasing)

If treatment failure is suspected, consult your healthcare provider. They may recommend retreatment with the same medication, trying an alternative medication, or investigating for crusted scabies which requires more aggressive treatment.

Returning to work and school

You become non-contagious after completing the first treatment application - typically after the medication has been on for the prescribed time (8-14 hours for permethrin) and washed off. Adults can return to work and children can return to school or childcare the day after completing the first treatment, though they should complete the full two-treatment course as scheduled.

What Are the Complications of Scabies?

The main complications of scabies are secondary bacterial skin infections from scratching (impetigo, cellulitis) and the psychological impact of persistent itching. In immunocompromised individuals, crusted scabies can develop, which is highly contagious and more difficult to treat.

While scabies itself is not dangerous, the intense scratching it causes can break the skin barrier, allowing bacteria to enter and cause secondary infections. The most common bacterial complications are impetigo (a superficial skin infection causing honey-colored crusts) and cellulitis (a deeper skin infection causing redness, warmth, and swelling). In some parts of the world, post-streptococcal glomerulonephritis (kidney inflammation) has been linked to scabies-related skin infections.

The psychological impact of scabies should not be underestimated. Chronic itching can lead to sleep deprivation, anxiety, depression, and social isolation. The stigma associated with scabies, though medically unfounded, can cause significant emotional distress. It's important for patients to understand that scabies is not related to cleanliness and can happen to anyone.

When to seek urgent care

How Can You Prevent Scabies?

Prevent scabies reinfection by treating all close contacts simultaneously, washing bedding and clothing in hot water, and avoiding close skin contact with infected individuals until treatment is complete. There is no way to become immune to scabies - you can be reinfected at any time.

Unlike some infectious diseases, there is no immunity to scabies. You can become infected multiple times throughout your life. The best prevention is avoiding prolonged skin-to-skin contact with infected individuals and ensuring all household members are treated when one person is diagnosed.

In healthcare and institutional settings, standard precautions and contact isolation are recommended for patients with suspected or confirmed scabies. Healthcare workers should wear gloves when providing direct care. For patients with crusted scabies, more extensive precautions including gowns may be necessary.

Preventing spread in households

• Treat all household members on the same day, even those without symptoms
• Wash all bedding, towels, and recently worn clothes in hot water and dry on high heat
• Avoid sharing towels, bedding, and clothing during and shortly after treatment
• Vacuum carpets and upholstered furniture, then discard the vacuum bag
• Seal items that cannot be washed in plastic bags for 72 hours