Scabies is an infestation of the skin with a mite known as Sarcoptes scabiei. Female mites are attracted to odor and warmth and settle into the folds of human skin. After creating a tunnel in the skin, the female deposits eggs, leaving behind a trail that looks like a pencil mark. When these eggs mature, the new mites begin to spread over the skin, causing intense itching.
Scabies is a contagious condition that is usually spread by skin-to-skin or sexual contact. People who live in close contact – such as children in day care facilities or schools, students in college dormitories, and older adults in nursing homes – are at increased risk for spreading or contracting scabies.
Intense itchiness is the symptom most often associated with scabies. It tends to worsen after a hot bath and at night when a patient is lying in bed. Many different conditions can cause similar symptoms, so the most effective way for a physician to diagnose scabies is to take a scraping of skin and analyze the sample using a microscope. This can reveal the presence of the mite responsible for scabies.
The only effective treatment for scabies is to use a medicated cream or lotion that kills the mites. This is applied over the patient’s entire body except the head (infants may require treatment on the hairline) and left on the skin for at least eight to 12 hours. It then is washed off. These medications kill the mites very quickly. Within just a few hours, patients will no longer be contagious and new marks should stop appearing within a couple of days.
About scabies
Scabies is a contagious skin condition. It is caused by tiny, eight-legged mites that burrow under the skin, resulting in intense itchiness. This skin infestation is found throughout the world and in all demographic groups. Poor hygiene is not necessary to contract scabies, although the disease is more prevalent in people who live in crowded conditions.
More than 300 million cases appear every year, according to the American Osteopathic College of Dermatology. The scabies mite – known as Sarcoptes scabiei – can attack any person regardless of age. Family households, schools and daycare facilities, college dormitories, nursing homes and other situations where people live in close day-to-day contact are particularly vulnerable to outbreaks of scabies. The condition is usually spread by skin-to-skin or sexual contact.
Mites are attracted to warmth and odor, and tend to settle in the folds of the skin. Once an adult female attaches to a human host, she can live for up to a month. Once away from its host, the mite dies within 48 to 72 hours. The time between exposure to the mite and the appearance of symptoms can take from six to eight weeks.
Adults and children can have different body areas affected by the mites. Infants and young children may have mites widespread over the body, including the head and face. Adults are normally affected only from the neck to the toes.
Scabies mites also can infect animals. However, the mite that infects animals is not the same mite that attacks people. Humans who come into contact with animal scabies are unlikely to develop a full-blown reaction, as these mites generally die quickly once they leave their animal host.
People who are elderly, have weakened immune systems or have neurological diseases may be more susceptible to a severe form of scabies known as Norwegian scabies, or crusted scabies. It is a form of scabies that appears as thick crusted plaques over the skin, particularly on the hands, nails, groin and scalp. This type of scabies infection is thought to be due to a reduced immunologic response to the mite.
Risk factors and causes for scabies
Scabies is the result of an infestation of a person’s skin by the Sarcoptes scabiei mite. Female mites dig under the skin and produce a tunnel, which is used to hold the mite’s eggs. After about three weeks, the eggs mature, and mites within them begin to move to the skin’s surface. The adult mites travel along the skin and mate on its surface. As the mites spread to other areas of the skin, the body’s immune system creates an allergic reaction that results in intense itchiness.
At this point, a person’s scabies is contagious and is often spread to others through close skin-to-skin or sexual contact. Less frequently, the mite causes infection through shared use of clothing or bedding.
People who are elderly or who have weakened immune systems may be more susceptible to a more severe form of scabies known as Norwegian scabies or crusted scabies.
Signs and symptoms of scabies
People who have no previous history of scabies may begin to experience symptoms about four to six weeks after their initial infection. Those who have been infected previously may begin to feel symptoms in as little as a few hours to a few days.
Intense itching is the symptom most often associated with scabies. This itchiness tends to worsen after a hot bath and at night when a patient is lying in bed. When the scabies mite burrows under the skin, it leaves a characteristic thin, irregular, wavy, reddish or darkened line on the skin that looks like a pencil mark. This is usually made up of tiny blisters or bumps.
The mite may infest any part of a patient’s skin, but tends to prefer to nestle in folds, such as between a person’s fingers, in the armpits or on the waist. Other common sites of infestation include:
Backs of elbows
Breasts
Buttocks
Inside wrists
Knees
Genital area
Shoulder blades
Soles of the feet
Navel
It is also common to find mites hiding under fingernails, as well as on the skin around rings, bracelets and watch bands.
The pattern of infestation may vary depending on the patient’s age. Babies tend to have widespread infections, with pimples appearing on the trunk and small blisters appearing over the palms of the hands and soles of the feet. Young children are more likely to experience infestation on the head, neck, shoulders, palms and soles, while older children and adults are more likely to be infested in the hands, wrists, genitals and abdomen.
A more severe form of scabies known as Norwegian scabies (also called crusted scabies) appears as vesicles (raised lesions) and a formation of thick crusts over the skin. Patients with this form of scabies usually are infested with many more mites than traditional scabies, but they may feel only slight itching or no itching at all.
In some cases, patients with scabies may scratch the skin too vigorously, causing a break in the tissue that allows a secondary bacterial infection to develop. This often takes the form of impetigo or cellulitis, which are caused by either staphylococci or streptococci bacteria. Skin that is scratched incessantly also may develop a scabbed and scaly appearance.
Patients experiencing the signs and symptoms of scabies should contact their physician. Individuals who have had close contact with someone who has been diagnosed with the condition should also seek medical attention.
Diagnosis methods for scabies
Patients are likely to seek medical care when they experience itching that they cannot bring under control. The physician will likely perform a complete physical examination and compile a thorough medical history of the patient.
Many different conditions can cause symptoms such as skin bumps and itchiness (e.g., eczema, hives). The scaly, thickly crusted rash associated with Norwegian scabies may also be misdiagnosed as psoriasis. Therefore, a physician trying to diagnose scabies will look for the additional telltale signs of the condition, such as “burrows”, slightly elevated, grayish, straight or curved lines on the skin.
A scraping of the skin can reveal the presence of mites, mite eggs or mite feces when the skin sample is examined under a microscope. However, diagnosing scabies is not always easy. In most cases, patients will have no more than a dozen mites on their body. For this reason, they are often missed during an examination. In such a case, people experiencing lasting scabies symptoms may want to return to the physician for another examination.
Treatment and prevention for scabies
There are no over-the-counter medications that are effective in treating scabies. Instead, patients must receive a prescription cream or lotion that is applied thoroughly over the patient’s entire body, including the head and under the fingernails. Infants and young children may also require treatment on the hairline if this area is infected. Patients should leave the medication on the skin for at least eight to 12 hours before washing. Hands also should not be washed during this time. Medication will likely be reapplied after about a week. Patients should not reapply the medication earlier than recommended by their physician. Overuse of scabies medication can lead to skin irritation.
These medications kill the mites very quickly. Within just a few hours, patients will no longer be contagious. New marks should stop appearing within a couple of days. In 95 percent of cases, the initial application of a cream or lotion medication rids the body of infestation, according to the American Osteopathic College of Dermatology. Physicians may also prescribe an antibiotic if a bacterial infection develops as the result of scratching.
Despite the quick treatment of mite infestation, itchiness generally continues for anywhere from a couple of days to as long as several weeks after the medication is first applied. Patients can take several steps to help reduce their symptoms. For example, they can soak in lukewarm water or apply a washcloth to areas of the skin that are itchy. Calamine lotion and antihistamines also are often effective in reducing symptoms. However, patients should not use these medications without first consulting a physician. Topical corticosteroids may also be recommended to help relieve itchiness.
Patients are also urged to wash items such as clothing, bedding and towels in hot, soapy water. The items should then be dried in high heat. Dry cleaning is another effective alternative. It is also advisable to vacuum the house (including carpets and upholstery) and throw away the vacuum bag when finished. Items that are not washable (e.g., toys) can be placed inside a sealed plastic bag and stored for two weeks. This will starve and kill any mites on these items.
It is important to eradicate scabies as completely as possible in both the patient and others who may have been infected by close contact with the patient. As a result, entire groups such as families, classrooms or nursing home residents may be asked to undergo treatment, even if no signs or symptoms of infestation are present.
If treatment efforts initially fail, they will be repeated until the mites are eradicated. In some cases, a patient’s mites are resistant to the prescribed medication and another form of treatment will be needed to effectively treat the condition.
Questions for your doctor regarding scabies
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to scabies:
Do my symptoms indicate scabies?
What methods will you use to determine if I have scabies?
Should I alert school/day care/college/nursing home officials about the infection?
Should everyone in my family be treated? What about the family pets?
How can others in the family reduce their odds of being infected?
What steps can I take to increase the odds that treatment will be effective?
When can I expect my symptoms to improve?
How can I reduce my itchiness while we wait for the infection to subside?
At what point will I no longer be contagious?
What steps should I take to make sure my house is mite-free?
How will I know if I have developed a secondary infection from scratching?
Will I need to return to a physician’s office later to make sure the treatment has been a success?
