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Scabies

What are scabies?
Scabies is a human skin condition caused by an infestation of tiny mites that burrow under the skin. Humans serve as a host for scabies by providing blood meals and an area on which to lay their eggs. Scabies infestation causes the skin to become irritated, itchy, and to develop a rash around the site of infestation. The rash results from an allergic reaction to the secretions of the mites. Scabies may be mistaken for psoriasis, eczema, rosacea, and/or other skin conditions with similar effects. This skin condition is also known as "seven year itch" and "Norwegian itch", a more serious form in which a crust forms on the skin. Mites that cause scabies on animals are different from the species found on humans and cannot cause scabies on humans.

What are scabies mites and what is their life cycle?

Scabies mites (Sacroptes scabei) belong to the arthropod class Arachnid. The mites are round and about 0.4mm long, with four pairs of pointed legs that have suction devices on the first two pairs of legs. The life cycle of a mite consists of four stages: egg, larva (six-legged), nymph (eight-legged), and adult (eight-legged). Development from egg to adult takes 10-14 days. Mites usually live up to a month. This particular mite is host-specific, meaning that it will only feed and complete its life cycle on a human. Humans are not at risk for contracting scabies mites from an animal or vice versa.

How are scabies spread?
Scabies is highly contagious and is spread though various methods. Skin-to-skin contact is the primary mode of infestation. Other ways that scabies can be contracted include sexual contact, sharing clothes, or using the unwashed bedding or towels of an infested person. They are commonly found on people in day care centers, nursing homes, and hospitals due to the close contact between caregivers and recipients.
What are the symptoms of scabies?
The symptoms of scabies are:
  • Intense itching of the skin, usually around the folds of the skin. The most common areas scabies occurs include the following: wrists, arms, elbows, knees, genitalia, between the fingers, around the waist, between buttocks, and under arms. Young children and infants may experience itching anywhere on the body. Itching is usually more prominent at night;
  • Red patches, pimples, bumps, rash, and/or blisters on the skin;
  • Short, dark lines across the skin;
  • Open sores from scratching, which may create a secondary bacterial infection;
  • More serious symptoms occur among immunocompromised individuals and the elderly. Larger areas of skin are infested with mites resulting in a crust (thickening of the skin), where thousands to millions of mites and eggs reside. The thick layer of skin is difficult to treat with topical medications. This is known as Norwegian (crusted) scabies.
How is scabies diagnosed?
If scabies is suspected, consult your medical provider immediately. Most medical providers will diagnose scabies by a skin sample taken from an infested area. The sample requires application of mineral oil on the skin and painless scraping of skin, which is then examined under a microscope to observe the presence/absence of mites, eggs, and/or their waste. It is possible that the test will come back negative because there are only about 10-15 mites living on an individual at once, except in the case of Norwegian scabies.
What is the difference between scabies and Norwegian scabies?
The difference between scabies and Norwegian scabies is the number of mites present. A regular scabies infestation involves about 10-15 mites. Norwegian scabies involves thousands to millions of mites living under crusted skin. Norwegian scabies is more difficult to treat with a topical medication because of the thick skin over the mites and their burrows.
What is the treatment for scabies?
There are various medicated lotions and ointments that can be prescribed by your medical provider. All the medications are applied topically to the infested area on the skin, unless otherwise directed by your doctor. The lotion is typically left on for 8-10 hours, and is very effective in killing mites. However, it is possible that itching may not subside for several weeks. Continuance of itching does not mean the medication did not work, since a person's body may take time to recover from the allergic reaction to the scabies mites.

The most common and effective treatment is a lotion containing 1 % or 5 % permethrin. Lindane is another medicated lotion that is prescribed less frequently because of its toxicity. Along with the medicated lotion, your doctor may suggest taking Benadryl to relieve the itch.

Wash all clothing, towels, and bed linens in hot water to decrease the chance of reinfestation. Items that cannot be washed should be sealed in a plastic bag for one to two weeks in order to kill any remaining mites.

How can I prevent scabies?
Scabies is highly contagious. To reduce chances of scabies infestation:

  • Exercise good personal hygiene (e.g., bathe regularly);
  • Wear clean clothes and do not share clothes with others;
  • Wash all bed linens and towels frequently in hot water (130°F) and soap or tightly seal non-washable clothing in plastic bags and leave for at least two weeks;
  • Avoid any physical contact with someone who has recently been diagnosed with scabies;
  • Vacuum all carpets and upholstered furniture.
Additional Information

For more information on scabies, call 311.

Last Updated: January 9, 2013