Skin parasites (PAIR-uh-sites) are tiny organisms that invade the skin, often causing irritation and itching.
Parasites are animals that live off of other living beings (including people), often feeding and reproducing on them. Some parasites thrive on human blood and cannot live long without it. Parasites may lay their eggs on people's skin. Before long, that person could become the host (an organism that provides another organism with a place to live and grow) for hundreds or more of the parasites.
Skin parasites are found worldwide and infest large numbers of people. For example, as many as 6 to 12 million people worldwide contract head lice every year, according to the Centers for Disease Control and Prevention (CDC). Head lice most often affect children in school and daycare settings.
There are many parasites that infest human skin, but lice, scabies (SKAYbeez), and chiggers are among the most common.
Also known as Pediculus humanus capitis (peh-DIH-kyoo-lus HYOO-mah-nus KAH-pih-tis), head lice are six-legged parasites with tiny claws that cling to hairs. They are found on the scalp, neck, and behind the ears. Lice lay visible whitish eggs called nits. In about seven days, the nits hatch into young organisms called nymphs (NIMFS). Nymphs grow up fast, and in just one week they mature into adult lice that must feed on blood to stay alive. Head lice may not cause any symptoms immediately, but as with other insect bites, the body reacts to the invaders, leading to itching and sores from scratching.
Anyone can get lice. The parasites are easily spread from person to person. Head lice are spread by close contact with a person who already has them. They also can be passed by sharing such items as combs, brushes, hats, barrettes, pillows, and headphones. Head lice are especially common in young children and their families. They may spread quickly among children in school or camp. Having lice is not a sign of dirtiness or poor hygiene.
Head lice do not cause serious medical problems. They usually are found on the scalp. Often they are seen at the back of the neck and around the ears. In a few cases, head lice are found on the eyelashes or eyebrows. The bite of the head louse can cause a minor allergic reaction. The first sign of trouble usually is severe itching on the part of the body where the lice are biting. It may take as long as two to three weeks for the itching to start. Although it may be difficult, a person with lice should try not to scratch, because doing so can spread the lice to other parts of the body. They can live for up to 30 days on a person.
Also known as Pediculus humanus corporis (peh-DIH-kyoo-lus HYOO-mah-nus COR-por-is), body lice are usually found in clothing and bedding from which they travel to the skin to feed. They are sometimes called clothing lice. Body lice usually are passed through contact with clothing and bedding in which the lice are living. They are more likely to be found in people who live in crowded conditions where clothes are not changed or washed very often.
Body lice are hard to see because they burrow into the skin. They are usually easiest to see in the seams of clothing, from which they travel to the skin to feed. Body lice are known to transmit three diseases: epidemic typhus, trench fever, and epidemic relapsing fever. Body lice are less common than head lice. They tend to spread in conditions such as refugee camps or after natural disasters when many people are crowded together in colder climates and lack bathing and laundry facilities.
Pubic lice, or Phthirus pubis (THEER-us PYOO-bus), invade the pubic hair and sometimes other body hair such as beards, eyebrows, eyelashes, and armpit hair. They often are called crabs because of their crablike appearance. Pubic lice usually are spread by close physical contact involving the genital area, such as sexual contact, so typically they are found in people who are sexually active. In rare cases, they may be picked up from bedding or clothing. Pubic lice cause intense itching, especially at night, when they feed by burying their heads into hair follicles * . The nits and adult lice can be seen on pubic hairs or surrounding skin. Pubic lice are not known to transmit any diseases; however, because they are usually found on sexually active people, anyone with pubic lice should be evaluated for the presence of other sexually transmitted diseases.
Scabies is a skin condition caused by mites that dig under the skin. Mites are eight-legged animals related to spiders, scorpions, and ticks. They are so tiny that they require a microscope to be seen. The scientific name for the scabies mite, or “itch mite,” is Sarcoptes scabiei. Its relatives cause mange (MAYNJ), an inflammation of the skin that results in hair loss in dogs, pigs, horses, and cows.
Scabies is a common contagious * skin condition that passes easily from person to person. Outbreaks of scabies, in which many people get infested at once, can occur in places such as nursing homes, child care centers, and dormitories. The scabies mite cannot live very long away from the body. It can be spread by skin-to-skin contact or by clothing or bedding that has been used very recently by an infected person.
The mites work their way under the top layer of skin and lay their eggs. Most people are not even aware of the intruders until intense itching begins two to six weeks later. Red pimple-like bumps appear on the skin, and there may be wavy lines on the skin tracing the mites’ paths, especially in the webbing between the fingers and in the skin folds at the back of the knees and on the inside of the elbows.
Chiggers are mites that tend to live in weeds, tall grass, or wooded areas. The chigger larvae (LAR-vee) feed on a variety of animals, including humans. The larvae crawl onto the skin of passersby and can use their tiny claws to grab onto human hair. They then attach to the skin (usually at the ankles, waist, or in skin folds) with hooked mouthparts and feed on skin cells. Unlike lice and scabies, chiggers feed on their host only for a couple of days, then let go and fall off. Chigger bites can cause a red bump that continues to grow in size, a skin rash, hives * , and severe itchiness. Sometimes the larvae are visible in the center of the bump.
Despite what many believe, people do not get skin parasites because of poor hygiene. Instead, skin parasites tend to spread in situations in which they can walk or fall from one person to another (or in the case of chiggers, from vegetation to human skin). The parasites often require relatively prolonged and close contact to move between people, and they spread most easily in crowded conditions, from sharing personal items, and from skin-to-skin contact.
Head lice in particular fall easily onto their next victims in close quarters. They also can infest hairbrushes, barrettes, hats, and sometimes clothes or bed linens. Other people become infested by using these items. Pubic lice spread mostly through sexual contact, but people also can get them from bed linens and clothes.
Scabies spread quickly in crowded living conditions or in places with lots of skin-to-skin contact (such as day care centers and nursing homes). Like lice, scabies can be passed through sexual contact and by sharing clothes, towels, and bed linens.
Doctors often diagnose skin parasite infestations just by spotting the parasites, their eggs, larvae, or characteristic red bumps on the skin. With scabies, a skin scraping might be taken to check for mites, eggs, and mite feces (FEE-seez, or bowel movements). However, this test is not always accurate because the mites may have moved from the spot that was scraped.
Over-the-counter and prescription lotions and shampoos (known as pediculicides, peh-DIH-kyoo-lih-sides) can be used to kill head lice. In some cases, treatment may need to be repeated or replaced with stronger medications because lice are becoming resistant to some treatments. Other people living in the same house with the infested person may be treated at the same time.
Pubic lice also are treated with a pediculicide, similar to the treatment of head lice. If the infestation includes the eyelashes, petroleum jelly is applied several times a day to the eyelids for a week or more.
Patients with scabies are given medicated lotions to apply over the entire body, and the lotion must stay on for eight to 12 hours. Chigger bites do not require any special treatment to heal, but antihistamines * may ease itching. Infestation with lice and scabies can persist until they are treated properly. Once treatment begins, patients are usually no longer contagious after a day or two, but sores and itching may continue for several weeks. Chigger bites heal quickly.
Complications of skin parasites are rare. Frequent or rough scratching of bites or sores can lead to bacterial infections like impetigo * . If lice spread to eyebrows or eyelashes, the eyelids may become infected. Norwegian, or crusted, scabies is a form of scabies that can be severe in people with weak immune systems * , such as those with a chronic illness and those who are elderly.
To avoid skin parasites, experts recommend that people take the following precautions:
To prevent the spread of parasites in a home when a family member has been diagnosed with an infestation, the following measures are recommended:
In addition, children who have skin parasites should stay home from school or day care until a day or two after they begin their treatment.
See also Bites and Stings • Hives • Impetigo • Parasitic Diseases: Overview • Skin Conditions: Overview • Sexually Transmitted Infections (STIs): Overview
Earlstein, Frederick. Scabies and Lice Explained: Causes, Prevention, Treatment, and Remedies All Covered! Los Gatos, CA: NRB Publishing, 2013.
Centers for Disease Control and Prevention. “Parasites – Lice.” http://www.cdc.gov/parasites/lice (accessed July 10, 2016).
Centers for Disease Control and Prevention. “Parasites – Scabies.” http://www.cdc.gov/parasites/scabies/index.html (accessed July 10, 2016).
MedlinePlus. “Parasitic Diseases.” U.S. National Library of Medicine. https://www.nlm.nih.gov/medlineplus/parasiticdiseases.html (accessed July 10, 2016).
American Academy of Dermatology. PO Box 4014, Schaumburg, IL 60168-4014. Toll-free: 866-503-7546. Website: https://www.aad.org (accessed July 10, 2016).
Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 800-232-4636. Website: http://www.cdc.gov (accessed July 10, 2016).
National Pediculosis Association. 1005 Boylston St., STE 343, Newton, MA 02461. Telephone: 617-905-0176. Website: http://www.headlice.org (accessed July 10, 2016).
World Health Organization. Avenue Appia 20, CH - 1211 Geneva 27, Switzerland. Telephone: 41 22 791 2111. Website: http://www.who.int (accessed July 10, 2016).
* hair follicles (FAH-lih-kulz) are the skin structures from which hair develops and grows.
* contagious (kon-TAY-jus) means transmissible from one person to another, usually referring to an infection.
* hives are swollen, itchy patches on the skin.
* antihistamines (an-tie-HIS-tuhmeens) are drugs used to combat allergic reactions and relieve itching.
* impetigo (im-pih-TEE-go) is a bacterial skin infection that usually occurs around the nose and mouth. It causes itching and fluid-filled blisters that often burst and form yellowish crusts.
* immune system (im-YOON) is the system of the body composed of specialized cells and the substances they produce that protect the body against disease-causing germs.