What is it?

Scabies is an infestation of the skin with a mite called Sarcoptes scabiei that lives under the top layer of the skin (stratum corneum). The itch and rash are caused by a hypersensitivity reaction to the mite and its feces/eggs.

What does it look like?

People with scabies are usually very itchy. The itching usually begins about 3 weeks after contact with the scabies mite and is usually worst in the evening/night. Skin findings include papules, nodules, burrows (lines in the skin where the mite has lived and traveled), and blisters/pustules. The most common locations are between the fingers, on the wrists, ankles, axillae, waist, groin, palms, and soles. In infants only, the lesions can also be seen on the head. Scabies nodules are a reactive process to the mite and are commonly seen in the groin and axillae (nodules on the scrotum or penis in a patient with diffuse itching are diagnostic).

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How do people get it?

Scabies mites are usually spread through skin-to-skin contact between people, but it is possible to get it from clothes or sheets that also have the mite. The mite can live for several days away from a person, so it is possible to contract scabies from contact with clothes or sheets that someone with scabies used several days before.

How is it diagnosed?

A diagnosis of scabies can often be made clinically based on a suggestive history (e.g. multiple cohabitants with similar rash) and with classic lesions such as burrows or scrotal nodules. However, in cases where the diagnosis is unclear, a scabies prep can be helpful. To do a scabies prep, clean a few suspected burrows and papules with alcohol and then scrape with a 15 blade scalpel. Because the mite lives under the stratum corneum, the scraping must be a bit more firm/deep than the very superficial scraping done to diagnose fungal infections; therefore, a small amount of bleeding is expected. The scraping is smeared on a glass slide and either KOH or mineral oil is placed on the slide before the cover slip is put in place. Mineral oil can also be placed on the skin or blade beforehand to help collect the scraped material more easily. With mineral oil, the mite will survive and may be seen moving on the slide. Additionally, it is easier to see eggs or feces when using mineral oil. Because each infested individual has only about 10 mites at any one time, it is usually necessary to scrape many papules at once to get a positive diagnosis. Scabies mite can also be seen with a dermatoscope. It is visible as a small dark triangle, known as the delta wing sign, at the end of a burrow.

How is it treated?

There are several treatments available for scabies. The most commonly used is 5% permethrin cream, which is applied to all skin from the neck down at bedtime. To be effective, the cream must be applied everywhere including between the fingers, under the nails, and in the groin area. In infants, it must be also be used on the scalp and face, being careful not to get it in the eyes or mouth. In the morning after the application of the cream, it should be washed off and all sheets and clothing/undergarments should be washed. This procedure is repeated one week later. Because scabies is so contagious, it is recommended to treat all members of the family and others who have had close contact with the patient. All close contacts should be treated at the same time. Clothing and linens used within the previous week can be washed in hot water or stored in a bag for 10 days to kill any mites that may be living there.