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Head lice: Overview

Last Update: December 3, 2015; Next update: 2018.

Introduction

Head lice are tiny parasites that live in our hair and feed on blood from our scalp. Their bites can itch and some people find them quite repulsive. Aside from that they are fairly harmless and do not carry disease.

Head lice mostly lay their eggs on hairs, close to the scalp. The next generation usually hatches within one week. The eggs laid by head lice are called nits.

Head lice can multiply and spread quickly. They are often unwelcome visitors at day care centers, kindergartens and schools. Once lice have settled on your scalp they do not go away on their own again. But there are a number of different effective treatments for getting rid of these bloodthirsty little creatures.

Illustration: Smaller than the head of a match: adult louse and nit

Smaller than the head of a match: adult louse and nit

Causes and risk factors

Head lice are most common in children. They almost always spread through direct body contact, for instance when children play with their heads close together. Although some people think head lice are a sign of uncleanliness, it does not matter to the lice whether your hair is clean or dirty. They feed on blood. So anyone can get head lice. But the association with uncleanliness can still be very embarrassing for parents and children affected by head lice.

Hair length has at most very little influence on your risk of getting head lice, but it is harder to find the lice in longer, thick and curly hair.

Prevalence

Head lice are quite common, especially among children between the ages of 3 and 12. Although no exact figures are available, it is estimated that about 2 to 4% of all children in Germany have head lice.

Larger European studies on head lice showed that nearly 10% of the children had head lice. It is also quite common for there to be outbreaks at kindergartens, day care centers and schools.

Diagnosis

An itchy scalp alone is not a definite sign that your child has head lice. The only way to tell for sure is to find living lice. Full-grown head lice are only 2 to 3 mm long. Their bodies are flat, wingless and usually grayish-brown. Unlike fleas, lice are not able to jump. But their six legs give them the ability to hold on tight to human hair and crawl along it. Because head lice are so small, it is difficult to see them in thicker areas of hair. It can help to carefully comb your hair using a lice comb. This works best if you do it while your hair is wet. A magnifying glass can help you detect lice that are still growing.

Nits are most commonly found on the back of your neck or behind your ears. They stick firmly to your hair, usually at a distance of less than one centimeter from the scalp. Nits laid further away usually do not survive. Other small objects found in hair, like dandruff or scabs, can be mistaken for lice. But dandruff and other small objects do not stick to the hair and will fall out when shaken.

Illustration: Head lice and nits in hair

Head lice and nits in hair

Prevention

The most important thing to do to prevent lice from spreading is to avoid head-to-head contact between children. Lice are not likely to spread through contact with objects because they need to feed on blood every three to four hours and they can usually survive for only one day when not close to the scalp. They often dry up after just a few hours. The eggs also need to be close to the scalp because warm temperatures are needed for them to be able to hatch into nymphs. Head lice that you find on combs are usually injured and no longer able to survive.

But there is a small chance they will be spread by using the same comb or brush, or wearing the same cap or hat. If you want to be very cautious, you can make sure that children do not share any of these things. Washing at 140 degrees (60 degrees Celsius) will kill off any remaining lice, but it is not necessary to disinfect your entire home. To be on the safe side, you could wash bedding and put stuffed animals away in a tightly sealed plastic bag for one day. This will kill off any remaining lice.

Treatment

Finding a living louse or eggs is the only sure way of knowing whether your child actually has lice or not. Only then can treatment be started. That way, children do not need to have unnecessary treatment and can avoid the possible side effects.

There are a number of different ways to get rid of lice:

Using a special comb is often not enough to get rid of lice for good. As long as there's a chance they may still have lice, children cannot be sent back to school. Using a lice comb can also be quite difficult and time-consuming. For this reason, it is usually considered as a measure to be used in addition to other treatment options.

Insecticides are generally effective. But over the years head lice have built up resistance to some of these products, so they are less effective than they once were. There are also silicone-based alternatives that do not contain any insect poison. These treatments cover the lice with a layer of oil, causing them to suffocate. Most of the plant-based treatments involve products made from oil too, but they are not as well tested.

Illustration: Head lice: life and reproductive cycle

Head lice: Life cycle and reproductive cycle

If your child still has a few nits after being treated for head lice, but you have not found any lice for a while, the parasites are most likely gone. Nits or parts of nits may stick to hair for weeks or even months after an acute case of head lice. You can tell how old the nits are based on their distance from the scalp. Hair grows at a rate of about one centimeter per month. So any nits that are more than one centimeter away from the scalp are probably older eggs that are no longer viable.

Everyday life

Head lice can spread quickly, so if your child has head lice it is a good idea to let anyone who comes into close contact with them know about it. In Germany, the parents or guardians of a child with head lice are required by law to notify public institutions like the kindergarten or school. You may feel a bit awkward about calling, but there's no reason to be embarrassed. Head lice are a frequent problem at most day care centers and schools.

According to German law, children who have head lice must stay out of kindergarten or school until they are free of lice. A child who has been given a treatment proven to be effective may return to kindergarten or school the next day. The Robert Koch Institute publishes a list of officially recognized treatments. Your pharmacist can also advise you. Many institutions only need spoken or written confirmation from the child's parents, stating that the child has been treated for lice. Some may require a note from the doctor, though.

Sources

  • Burgess I, Silverston P. Head lice. Clin Evid 2015; 01: 1703.
  • Devore CD, Schutze GE; Council on School Health and Committee on Infectious Diseases, American Academy of Pediatrics. Head lice. Pediatrics 2015; 135(5): e1355-1365. [PubMed: 25917986]
  • Infektionsschutzgesetz (IfSG). Infektionsschutzgesetz.
  • Robert Koch-Institut (RKI). RKI-Ratgeber für Ärzte. Kopflausbefall. November 17, 2008.
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)

IQWiG (Institute for Quality and Efficiency in Health Care)

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