The Sarcoptes scabiei mite is a parasite that depends on humans to live. Mites burrow into the skin, lay eggs and leave behind droppings, all of which cause a hypersensitivity reaction in the skin, resulting in an intensely itchy rash. Eggs hatch within a few days, releasing larvae that continue the cycle. Because scabies infection can last for months to years without treatment, some people think that the term "seven-year itch" was coined to describe scabies in infected soldiers returning after World War I (other origins of this term relate to marriage infidelity resulting in various sexually transmitted diseases, such as syphilis).
Diagnosis of ScabiesThe diagnosis of scabies is usually made based on a person’s symptoms and the appearance of the skin rash. People with scabies typically have an "all over" itchy rash, although the rash often does not affect the face or scalp. The itching and rash may be more intense between the webs of the fingers, in the armpits, over the joints of the wrists and elbows, at the waistline, and in the groin and buttock areas. The rash appears as small bumps, or nodules, as well as small raised lines, or burrows, where the mites have burrowed into the skin. After these areas have been scratched, there also could be patches of eczema and even bacterial skin infections (such as impetigo).
It is possible to take a skin scraping or biopsy in order to see the mite under a microscope. This is the only sure way to make the diagnosis of scabies, although it is not typically done in most healthcare settings. In unusual cases or if the treatment of scabies is not successful, it may be important to make an accurate diagnosis by seeing the mite from a skin sample.
Treatment of ScabiesTreatment is quite easy for most people infected with scabies, and can be done with either topical or oral medications. According to the United States Food and Drug Administration (FDA), the preferred treatment is with permethrin cream (Elimite), which is applied to the entire body from the neck to the toes, and washed off after 8 to 14 hours. Studies have shown that permethrin results in a scabies cure in approximately 91% of people, although some people may require another application of permethrin cream 14 days later if symptoms persist. Permethrin is generally considered to be safe with few side effects (some itching and stinging may occur) and is indicated for use in children as young as 2 months of age.
Lindane cream (Kwell) is considered a second-choice treatment for scabies according to the FDA, given its potential side effects of seizures and muscle spasms; this therapy is not available in many parts of Europe for this reason. Lindane is also applied to the skin from the neck to the toes and washed off after 8 hours. It is nearly as effective as permethrin, with studies showing it can cure scabies in 86% of people. Other topical therapies not approved by the FDA for scabies include benzyl benzoate, crotamiton (Eurax), allethrin (pyrethrin topical spray), precipitated sulfur, and tea tree oil (as a natural therapy).
Occasionally, topical treatments for scabies aren’t effective, or cannot be tolerated because they are messy, may cause burning and stinging, or if the skin is so damaged that the topical medicine will be absorbed and result in serious side effects. In these situations, a single dose of oral ivermectin (Stromectol) is a safe and effective treatment for scabies. A single dose results in a scabies cure in approximately 70% of people; repeating the dose 14 days later increased the cure rate to 95% of people.
While the above treatments are effective at killing the scabies mites, the allergic reaction in the skin may persist for days to weeks due to the presence of dead mites, egg castings and mite droppings in the skin. Therefore, the use of topical corticosteroid creams may be helpful in reducing itching even though the mites have been killed.
Prevention of Scabies Re-InfectionIt is possible for a person to be re-infected with scabies if they don’t follow a few simple steps after the use of a topical or oral treatment for scabies. First, other members of the household, as well as any sexual partners, should be treated for scabies, even if they don’t have any symptoms. Next, clothing and bedding should be machine-washed in hot water and dried in a clothes dryer the day after treatment. Any clothing, bedding or upholstered furniture that has come into contact with an infected person, but cannot be washed, should be covered with plastic for at least 48 to 72 hours. If the mites don’t come into contact with people for at least this long, they will not be able to survive.
Read more about the many causes of itching.
Chosidow O. Scabies. N Engl J Med. 2006;354:1718-27.
Alergant CD. The Seven-Year Itch. Br J Vener Dis. 1961;37(3):200-1.
DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.