Scabies

What causes scabies?

Scabies is caused by a mite called Sarcoptes scabiei. A mite is like a tiny insect, and with scabies it's a parasite, meaning it lives off the host (a human) with no benefit to the host. The mites burrow into your skin, often through your hands, and then spread around your body.

Scabies mites

Scabies mites are so tiny, you can't see them with the naked eye. 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). With the naked eye you might be able to see them as a speck.

The female mites tunnel into the skin and lay eggs. About 40-50 mite 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.

Most of the symptoms of scabies are due to your immune system's response to the mites, or to their saliva, their eggs or their poo (faeces). In other words, the rash and the itching are mostly caused by your body's allergic-like reaction to the mites, rather than the mites themselves.

The average number of mites that can live on an infested person is 12.

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Scabies symptoms

Itching

This is the main symptom of scabies. This is often severe and tends to be in one place at first (often the hands), and then spreads to anywhere you tend to touch: your neck, your tummy (abdomen), your chest. It often focuses on your belly button or the tops of your legs (your groin). The itch is generally worse at night and after a hot bath. You can itch all over, even with only a few mites, and even in the areas where the mites are not present.

Mite tunnels

These tunnels (burrows) 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.

Scabies rash

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, the 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

Scratching due to intense itching can cause minor skin damage. In some cases the damaged skin becomes infected by other germs (bacteria). This is 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 a reaction (allergy) to the mites (or their saliva, poo (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 look like?

The visible symptoms of scabies include blotchy red rashes that tend to form on the thighs, abdomen, and lower back, though they can form anywhere on the body. Additionally, thin grey lines between 2 mm and 10 mm long will typically be seen between the fingers and on the hands.

Scabies on hand and fingers

By Gzzz (Own work), CC BY-SA 4.0, via Wikimedia Commons

Scabies on the arm

By Steschke (Own work), CC BY-SA 3.0, via Wikimedia Commons

Symptoms of recurring scabies

The itch and rash normally take 2-6 weeks to develop when you have a first scabies infection. However, if you have scabies and it is cleared with treatment, and then you catch it again, the symptoms may be slightly different.

In such instances the rash and itching develop much more quickly - often within a day or two. This is because the first scabies infestation has already sensitised your immune system. It then reacts much more quickly with this second bout of scabies.

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. 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.

You are unlikely to catch scabies from bedding and towels unless you use them immediately after being used by someone with scabies. However, just in case, 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 physical contact.

Crusted scabies (Norwegian scabies)

Crusted scabies - also called Norwegian scabies, is unusual, and most people who develop scabies do not get this type of scabies.

It is a more severe form of scabies with a hyperinfestation of lots of scabies mites. This means that there are thousands or millions of the mites, causing excessive scaling and flaking of the skin. Because there are so many mites, and because the skin is flaking off, scabies can be spread to others extremely easily. The rash is crusting (and looks a bit like psoriasis). It can be very extensive and can, if severe, lead to serious secondary bacterial skin infections.

Crusted scabies mainly occurs in people who have a poor immune system (are immunocompromised). The types of people who might get crusted scabies include:

• People with HIV/AIDS.
• People having chemotherapy.
• Frail people who are elderly or ill due to other conditions.
• Those who are poorly fed (malnourished).
• Those with learning difficulties (because they cannot comprehend or respond to the itch).
• People who have nerve-related problems (because they cannot feel the itch).

What causes crusted scabies?

Crusted scabies is more easily transmitted through contact with towels, bedding and upholstery. In crusted scabies, the mites can survive for a few days away from their host. Even minimally exposed people, such as cleaners and laundry personnel, are at risk from crusted scabies and need insecticide treatment if they are working in an institution with an outbreak.

An outbreak in an institution with many vulnerable people, such as a nursing home, can be extremely challenging. It is likely that all residents and all staff would require treatment.

A healthy person and young children with a normal immune system would develop 'normal' scabies if infested with the scabies mite following contact with someone who had crusted scabies.

Crusted scabies may be impossible to eradicate in people with HIV infection, and recurrences are common.

Scabies diagnosis

To diagnose scabies, a pharmacist will usually just look at the rash, and by the story of itchy spots spreading around your body. A doctor will often be able to recognise the typical appearance of the scabies rash, although in the early stages it can resemble eczema.

Often, a doctor will find one or more mite tunnels (burrows) on the skin to confirm the diagnosis. Sometimes the doctor will rub some ink on the skin and then wipe it off. If there are burrows in that area of skin, the ink will move along the burrow under the skin in those diagnosed with scabies. It will be visible as a line after the rest of the ink has been wiped away.

Could it be something other than scabies?

It is sometimes difficult to tell the difference between the rash caused by scabies and the rashes of some other skin conditions. For example, sometimes the itchiness on the hands and wrists is quite similar to eczema. Sometimes doctors will treat the itching with steroid creams, which work well in eczema but will not help scabies at all.

If itching and a rash develop in several people who live in the same home at about the same time then scabies is a likely cause.

Do I need to see a doctor for scabies?

If you are confident that you have scabies - you may have seen the tunnels (burrows) on your skin, or perhaps you have had it before - then you don't need to see your doctor. Treatments for scabies are available to buy from a pharmacy.

Who should be treated for scabies?

Scabies can stay in your skin for ever 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.

Scabies treatment

Scabies is curable. The usual way to treat scabies is with permethrin cream. Permethrin is an insecticide that kills the mites. This is known to be the treatment that works the best. If permethrin cannot be used, an alternative is to use a lotion called malathion liquid. (For example, some people may be allergic to permethrin.)

You can buy both of these products from pharmacies. You can also get them on prescription from a doctor. They are easy to apply and normally work well if used properly.

Re-apply the same treatment seven days after the first application. This helps to make sure that all the mites are killed.

Self-help tips

• Read the leaflet that comes with the product, for exact instructions as to where to apply. Usually treatment is applied to your whole body, including the scalp and face, whilst other treatments are to be applied just from the neck down. Remember to include awkward places such as the back, soles of the feet, between fingers and toes, under fingernails, and the genitals. Pay special attention to the areas where mite tunnels (burrows) most commonly occur. That is, in between the fingers, the front of the wrists and elbows, beneath the breasts, the armpits and around the nipples in women.
• An adult needs at least 30 g of cream or 100 ml of lotion to cover the whole body. So, for two applications you will need at least 60 g of cream or 200 ml of lotion per adult.
• Apply cream or lotion to cool dry skin (not after a hot bath).
• The cream or lotion should be left on for the full recommended time. Permethrin cream should be left on for 8-12 hours. Malathion lotion should be left on for 24 hours.
• Children should stay off school until the first application of treatment has been completed.
• If you wash your hands or any other part of your body during the treatment period, you should re-apply the cream or lotion to the washed areas.
• Breastfeeding mothers should wash off the lotion or cream from the nipples before breastfeeding, and re-apply treatment after the feed.
• Permethrin cream is not usually used for babies under the age of 2 months, and malathion is not usually used under the age of 6 months.
• Put mittens on babies to stop them licking the cream or lotion off their hands.
• Clothes, bedding, and towels should be machine-washed at 50°C or above after the first application of treatment. This kills the scabies mites. Keep any items of clothing that cannot be washed, in plastic bags for at least 72 hours to contain the mites until they die. Alternative options to kill the mites on clothes, towels and linen are to iron the item with a hot iron, dry cleaning, or putting items in a dryer on the hot cycle for 10-30 minutes. It is not necessary to fumigate living areas or furniture, or to treat pets.
• Some people who develop a secondary skin infection may also need antibiotics. If you suspect this is the case, you should consult a doctor.

When to see a doctor for scabies

See a doctor if the itch persists longer than 2-3 weeks after treatment. Sometimes the first treatment does not work, and a different one is then needed. The most common reasons why treatment fails, and scabies returns, are:

• The cream or lotion is not applied correctly for the recommended time.
• A close contact is not treated at the same time and the infection is passed back.

How long does it take for scabies to go?

It is normal to take up to 2-3 weeks (and sometimes up to six weeks) for the itch to go completely after the mites have been killed by treatment. This is because your skin reacts to the mites and takes a while to settle down, even once the mites have been killed.

Also, even after successful treatment, in a small number of cases there remain some itchy brownish-red lumps (nodules) up to 2 cm in diameter. If these remain, they most commonly occur on the genitals and armpits. These lumps are neither infectious, nor mean that the mite is still present. They occur in some cases as a prolonged skin reaction to the scabies mite. If they occur, they usually go within three months but occasionally last up to one year.

How to relieve scabies itch

Itching can be a distressing symptom. It can be eased either with topical treatments that you apply to the skin (such as creams or lotions), or with medication taken by mouth. Your GP or pharmacist can usually give advice regarding suitable products. Even cold moisturisers (emollients), especially if they contain menthol, can provide temporary relief. Avoid applying strong steroid creams, especially if the diagnosis of scabies is uncertain.

• Crotamiton cream or lotion has soothing qualities and may help to relieve itch. Apply crotamiton 2-3 times a day (but only once a day for children less than 3 years old).
• Hydrocortisone cream. This is a mild steroid cream that may ease any inflammation and help to ease itch. It can be bought from the chemist, or obtained by prescription. It can be applied once or twice per day, for up to a week.
• An antihistamine medicine that makes you drowsy, such as chlorphenamine. This does not ease the itch directly, but can help you to sleep if itching is a problem at night (particularly for children). It is not licensed for this use but can be safely used under the direction of a doctor.