Skin Parasites

Skin parasites (PAIR-uh-sites) are tiny organisms that invade the skin, often causing irritation and itching.

What Are Skin Parasites?

Parasites live off other living things (including people), often living, feeding, and reproducing on them. Some parasites thrive on human blood and cannot live long without it. 'When these parasites latch onto someone's skin, they may lay their eggs there. Before long, that person could become the host (an organism that provides another organism, such as a parasite or virus, with a place to live and grow) for hundreds or more of the parasites.

This image shows a magnification of one of the eggs laid by head lice. These eggs, called "nits," are visible to the naked eye. The term "nit-pick," which means to be concerned with insignificant details, derives from the process of taking the tiny eggs out of the hair by hand, a method used for centuries before more effective treatment was widely available.

Custom Medical Stock Photo, Inc.

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 U.S. Centers for Disease Control and Prevention. Head lice most often affect children in school and daycare settings.

What Are Some Common Skin Parasites?

There are many parasites that infest human skin, but lice, scabies (SKAY-beez), and chiggers are among the most common.

Head lice

Also known as Pediculus humanus capitis (peh-DIH-kyoolus 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 7 days, the nits hatch into young called nymphs (NIMFS). Nymphs grow up fast, and in just 1 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.

Pubic lice

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 crab-like appearance. Pubic lice cause intense itching, especially at night, when they feed by burying their heads into hair follicles^*. The nits or adult lice can be seen on pubic hairs or surrounding skin.

Scabies

Microscopic Sarcoptes scabiei (sar-KOP-teez SKAY-be-eye) mites cause an infestation called scabies. 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 2 to 6 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 the inside of the elbows.

Chiggers

Chiggers are mites that tend to live in weeds, tall grass, or wooded areas. The chigger larvae (LAR-vee, immature mites) 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 or waist or in skin folds, with hooked mouthparts and feed on skin cells. Unlike lice and scabies, chiggers only feed on their host 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.

How Are Skin Parasites Spread?

Despite what many believe, people do not get skin parasites because of poor hygiene. Instead, skin parasites tend to spread in situations where 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. If other people use these items, they can become infested as well. Pubic lice spread mostly through sexual contact, but people also can get them from bed linens and clothes.

Scabies spreads quickly in crowded living conditions or in places with lots of skin-to-skin contact (such as daycare centers and nursing homes). Like lice, scabies can be passed through sexual contact and by sharing clothes, towels, and bed linens.

Diagnosis and Treatment

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 8 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 usually are no longer contagious after a day or two, but sores and itching may not disappear for a couple of weeks. Chigger bites heal quickly.

Can Skin Parasites Cause Medical
Complications?

Complications of skin parasites are rare. Frequent or rough scratching of bites or sores can lead to bacterial infections, such as 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 elderly people.

How Can People Prevent Infestation with
Skin Parasites?

To avoid skin parasites, experts recommend that people:

• shower daily, wash hands frequently, and wear clean clothes
• avoid anyone who has lice or scabies until that person is treated
• never share brushes, hats, bed linens, or clothes
• practice abstinence (not having sex); birth control does not prevent pubic lice or scabies
• avoid chigger-infested areas and wear socks, long pants, and long sleeves in wooded or grassy areas

To prevent the spread of parasites in a home when a family member has been diagnosed with an infestation, it is wise to:

• wash bed linens, towels, and clothes in hot water, then dry them on high heat
• vacuum the entire house, then throw the vacuum cleaner bag away
• disinfect combs and hair items
• seal items that cannot be cleaned in airtight plastic bags for 2 weeks; at the end of that time, any parasites on those items will have died

In addition, children who have skin parasites should stay home from school or daycare until a day or two after they begin their treatment.

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