Scabies Causes, Symptoms, Diagnosis, Treatment, Prevention

Scabies Causes, Symptoms, Diagnosis, Treatment, Prevention

What is scabies?

Scabies is caused by a mite (like a tiny insect) called Sarcoptes scabiei. The mite is a parasite, meaning it lives off the host (a human) with no benefit to the host.

Scabies mites are tiny. They have a cream-coloured body, bristles and spines on their back, and four pairs of legs. The female mite is bigger (about 0.4 mm x 0.3 mm) compared with the male (0.2 mm x 0.15 mm). The female mites tunnel into the skin and lay eggs. About 40-50 eggs are laid in the lifetime of a mite. The eggs hatch into larvae after 3-4 days, these then grow into adults within 10-15 days. Less than one in 10 eggs becomes an adult scabies mite.

Most of the symptoms of scabies infestation are due to the immune system response to the mites themselves, their saliva, their eggs or their faeces.

The average number of mites on an infested person is 12. Neglected children with scabies in underprivileged communities may have 100s of mites.

Read more: Scars Causes, Types, Symptoms, Diagnosis, Treatment, Home Remedies

Causes of Scabies

Scabies is a highly contagious condition. If you have close contact with a person infested with the scabies mite, your chances of catching it are fairly high. Crowded living conditions, close body contact (e.g., sleeping in the same bed), even holding hands for a while can easily allow the mite to spread from one person to another.

Since the scabies mite won't live away from a human body for more than a few days, direct contact is a much more likely source of transmission than clothing, bedding, or towels. The mites that cause scabies live specifically on humans - they can't be transmitted to or caught from animals, such as dogs.

A female mite lays 3 to 4 eggs per day, just under the surface of the skin. It takes about 2 weeks for these eggs to develop into larvae and finally adults, after which the adults emerge to the surface of the skin to mate. Once mating is complete, the adults reinvade the skin of their host or another person. The presence of the burrowing adult mite, eggs, and larvae cause a terrible itch. The number of infesting mites averages 5 to 10 but varies depending on the person's hygiene.

There is a severe variant of scabies called Norwegian scabies (crusted scabies). It is usually seen in people with weakened immune systems (such as people with AIDS), or can occur in outbreaks in nursing homes or hospitals. In theses cases, the number of infesting mites may be in the thousands.

Another form of scabies, called scabies incognito, causes an extensive infestation due to corticosteroids (e.g., betamethasone*, hydrocortisone, desonide) applied to the skin.

How do you get scabies?

You need close skin-to-skin contact with an infected person to catch scabies. This is because the scabies mite cannot jump or fly.

Most cases of scabies are probably caught from prolonged hand-holding with an infected person. The hand is the most common site to be first affected.

Close skin-to-skin contact when having sex is another common way of catching scabies.

The skin-to-skin contact needs to be for a reasonable time to catch the mite. Therefore, you are unlikely to catch scabies from an infected person by casual short contact such as a handshake or a hug. The rate of transmission (spread) is higher the greater the number of mites.

The mites live in skin and can survive away from the host human for about 24-36 hours. You are unlikely to catch scabies from bedding and towels unless you use them immediately after being used by someone with scabies. However, due to the potential risk, it is best to treat bedding and towels by hot washing (described later).

Sometimes outbreaks of scabies occur in places such as nurseries and residential homes, where people are in regular close contact.

How is scabies spread?

Scabies mites  camera spread by close contact with someone who has scabies. Scabies can also be spread by sharing towels, bed sheets, and other personal belongings.

Scabies often affects several family members at the same time. You can spread it to another person before you have symptoms.

Can you catch scabies from a dog or cat?

Dogs and cats are infected by different types of mites than those which infect humans. Animals are not a source of spread of human scabies. Scabies on dogs is called mange. When canine or feline mites land on human skin, they fail to thrive and produce only a mild itch that goes away on its own. This is unlike human scabies which gets worse and worse unless the condition is treated.

What are risk factors for scabies?

Scabies can infest any human who comes in contact with the mites. The only known risk factor is direct skin contact with someone who is infested. The contact one experiences in social or school settings is not likely to be sufficient to transmit the mites. Sexual or other close contact (such as hugging) is required to spread the condition. The condition does appear in clusters, so outbreaks may occur within a given community.

Scabies symptoms

Mite tunnels (burrows)

These may be seen on the skin as fine, dark, or silvery lines about 2-10 mm long. They most commonly occur in the loose skin between the fingers (the web spaces), the inner surface of the wrists, and the hands.

However, they can occur on any part of the skin. You may not notice the burrows until a rash or itch develops.


This is often severe and tends to be in one place at first (often the hands), and then spreads to other areas. The itch is generally worse at night and after a hot bath. You can have widespread itching, even with only a few mites.


The rash usually appears soon after the itch starts. It is typically a blotchy, lumpy red rash that can appear anywhere on the body. The rash is often most obvious on the inside of the thighs, parts of the abdomen and buttocks, armpits, and around the nipples in women. The appearance of the rash is often typical.

However, some people develop unusual rashes which may be confused with other skin conditions.


Scratching due to intense itching can cause minor skin damage. In some cases the damaged skin becomes infected by bacteria - a secondary skin infection. If skin becomes infected with bacteria it becomes red, inflamed, hot, and tender.

Aggravation of pre-existing skin conditions

Scabies can worsen the symptoms of other skin conditions, particularly itchy skin problems such as eczema, or problems such as psoriasis. Scabies can be more difficult to diagnose in these situations too.

Note: the itch and rash of scabies are due to an allergy (reaction) to the mites (or their saliva, faeces or eggs). Scabies symptoms usually take 2-6 weeks to occur after you are first infected. The itch and rash can develop on any part of the skin, away from where the mites are actually burrowing. This means that you are infectious (and can spread scabies) before you even know you have scabies.

What does scabies feel like?

It is important to note that symptoms may not appear for up to two months after being infested with the scabies mite. Even though symptoms do not occur, the infested person is still able to spread scabies during this time. When symptoms develop, itching is the most common symptom of scabies. The itch of scabies is insidious and relentless and often worsens over a period of weeks. The itch is typically worse at night. For the first weeks, the itch is subtle. It then gradually becomes more intense until, after a month or two, sleep becomes almost impossible.

What makes the itch of scabies distinctive is its relentless quality, at least after several weeks. Other itchy skin conditions -- eczema, hives, and so forth -- tend to produce symptoms that wax and wane. These types of itch may keep people from falling asleep at night for a little while, but they rarely prevent sleep or awaken the sufferer in the middle of the night.

How did I get scabies?

By direct, prolonged, skin-to-skin contact with a person already infested with scabies. Contact must be prolonged (a quick handshake or hug will usually not spread infestation). Infestation is easily spread to sexual partners and household members. Infestation may also occur by sharing clothing, towels, and bedding.

Diagnosing Scabies

Mite burrows can often be detected. A doctor might put a drop of mineral oil onto a burrow and take a light scraping of the skin in that area. Mites, or their eggs and feces, can then be seen under a microscope.

When it's hard to see the burrows, a special blue or black ink can be applied to the skin. Most of the ink can then be blotted away from the surface, and only the burrows will retain the colour.

Wood's light is another diagnostic tool - when a specific antibiotic solution is applied to the skin and the surface is then wiped clean, this particular wavelength of light allows the burrows to be viewed by a doctor.

Because the scabies rash has a similar appearance to eczema, psoriasis, or rashes caused by insect bites, it's sometimes misdiagnosed. Scabies might only be identified when a person hasn't responded to creams to treat these other conditions. Another factor that characterizes scabies is extreme itchiness, even when there's very little visible rash.

Treating and Preventing Scabies

To prevent getting scabies in the first place, try to avoid direct contact with somebody who's infested. Be wary of using public areas such as tanning booths unless you're sure that they've been disinfected.

A one-time application of permethrin cream or lotion to the skin is usually effective in curing scabies, but a second application is recommended after a week to ensure all mites are killed. The whole body has to be cleaned (with warm water, not hot) and covered with the cream. Clean clothes should be worn during treatment, which lasts 8 to 14 hours, and then again after the cream has been washed off.

Clothes worn during the 3 days before treatment and any used bed sheets or towels should be washed in hot soapy water and then placed in the dryer on the hot cycle to kill both the mites and their eggs.

Get special instructions from your doctor or pharmacist about how much cream infants or young children need. A small amount of permethrin can be absorbed through the skin, and might come out in breast milk. If you're pregnant or breast-feeding, talk to your doctor about an alternative treatment.

In the past, another medication called lindane was used to treat scabies. It is not used very frequently now because it can cause neurotoxic side effects such as seizures.

After treatment, the itching won't go away immediately and might last for several weeks. This can be relieved with antihistamines, mild soaps, or prescribed corticosteroid lotions. But if you still feel intense itching after a month, you should see your doctor again as you may need to be retreated.

It's a good idea for everyone living under the same roof to be treated at the same time. This will lessen the chances of reinfection with the scabies mite. Disinfect your home, and wash all clothing and linen in hot water and then dry on a hot cycle. You could also put clothes, linens, toys, or household articles in a sealed plastic bag for a week. The pest will die off and the clothes can be worn again.

Who should be treated?

Scabies will persist indefinitely if not treated. Treatment is needed for:

  • Anybody who has scabies AND ...
  • All household members, close contacts, and sleeping/sexual partners of the affected person - even if they have no symptoms. This is because it can take up to six weeks to develop symptoms after you become infected. Close contacts may be infected, but have no symptoms, and may pass on the mite.

Note: everyone who is treated should be treated at the same time - that is, on the same day.

Did my pet spread scabies to me?

No. Pets become infested with a different kind of scabies mite. If your pet is infested with scabies, (also called mange) and they have close contact with you, the mite can get under your skin and cause itching and skin irritation. However, the mite dies in a couple of days and does not reproduce. The mites may cause you to itch for several days, but you do not need to be treated with special medication to kill the mites. Until your pet is successfully treated, mites can continue to burrow into your skin and cause you to have symptoms.

How soon after infestation will symptoms begin?

For a person who has never been infested with scabies, symptoms may take 4-6 weeks to begin. For a person who has had scabies, symptoms appear within several days. You do not become immune to an infestation.

How soon after treatment will I feel better?

Itching may continue for 2-3 weeks, and does not mean that you are still infested. Your health care provider my prescribe additional medication to relieve itching if it is severe. No new burrows or rashes should appear 24-48 hours after effective treatment.

What is Norwegian or crusted scabies?

Norwegian scabies, or crusted scabies, is a severe form of scabies first described in Norway. Crusted scabies almost always affects people with a compromised immune system and is observed most frequently in the elderly, those who are mentally or physically disabled, and in patients with AIDS, lymphoma, or other conditions that decrease the effectiveness of the immune response. Due to the poor function of the immune system, an individual may become infested with hundreds of thousands of the mites. The lesions of this distinctive form of scabies are extensive and may spread all over the body. The elbows, knees, palms, scalp, and soles of the feet are most commonly the original sites of involvement, and the scaly areas eventually take on a wart-like appearance. The fingernails can be thickened and discolored. Interestingly, itching may be minimal or absent in this form of scabies.

A particular danger of crusted scabies is that these lesions often predispose to the development of secondary infections, as with staphylococcus or streptococcus bacteria.