This is a common itchy skin condition that caused by invasion of the skin by the mite Sarcoptes scabei. It is spread by close  skin-to-skin contact (e.g. sleeping together). In general infectivity is low, so casual contact will not usually spread the infestation. The itching is triggered by an allergic reaction to the scabies mite. In a typical infestation you may harbour approximately ten mites on the body.

Along with the itching you may see short (a few millimetres long) greyish white linear tracks on the finger webs, sides of the fingers, wrists, elbows, front of the armpit, around the navel area, and nipples. These are burrows where the mite lays its eggs. Burrows are rarely seen on the buttocks and male genitalia - instead there may be small, firm, red lumps.

The first symptom is often severe and persistent itching, often worse at night and after bathing. The itching is due to an allergic response to the mite and may be present for several weeks before the rash appears.. By the time patients see the doctor there may be a widespread rash with many small lumps, often with scratch marks and dermatitis that may become infected.

In the first attack you may have the mite on your skin for 3-6 weeks before you notice symptoms, but this is much shorter in subsequent attacks - possibly as low 24 hours because you are already allergic to the mite.

Norwegian Scabies

Some people are vulnerable to more severe infestation where the number of mites can increase 10,000 fold. These people include those whose immunity is suppressed (e.g. in AIDS or as a result of drug treatment), those who are immobile or paralysed (and cannot scratch), confused patients (e.g. with dementia) and those living in institutions (e.g. nursing homes). In this form of scabies the rash is more florid with lots of scaling and can affect the face, scalp and palms of the hands - areas which are usually spared in simple infestation. There may be generalised redness of the skin and the condition may have been present for months. This type of scabies is highly contagious and can easily be spread to carers handling and washing clients with subsequent spread around the community. Because of the large number of mites in this condition, frequent applications of skin pesticides may be necessary and indeed it may be more appropriate to have the condition treated with an oral drug like ivermectin under a dermatologist's supervision.

Pesticides used for treatment

These include: Malathion and Permethrin. You can buy lotions to treat scabies over the counter at the chemist. 100ml should be sufficient for one adult. Apply the lotion with a small paint brush or cotton wool ball and allowed to dry before redressing. This is best done when the skin is cold, so do not do this after a bath or hot shower. This is to reduce absorption of the lotion into your bloodstream taking it away from the skin where it is needed. All the preparations are toxic to some extent and care should be taken in their use, with particular care being taken to avoid accidental ingestion or contact with eyes or broken skin. Alcohol based lotions can trigger asthma in susceptible individuals and in this situation use an alternative water based preparation. The entire body must be treated below the jaw line, including the soles of the feet! Pay particular attention to the webs of fingers and toes and brush lotion under the ends of nails. The application can be washed off after 24 hours. Do not wash your hands before this or you will wash the lotion away. One application may be sufficient providing it has been done properly but because treatment is often unsuccessful you may consider a second treatment one week later sensible. Clothing and bed linen should be washed normally and all household and close contacts treated. Ask a doctor before treating children under 6 months old and note that permethrin should be avoided during pregnancy or breast-feeding.

Itching may continue for several weeks and is usefully treated with crotamiton cream - Eurax ® - which also has mild activity against scabies. If the skin is badly scratched, calamine lotion may be less irritating.