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LICE

34 articles

What are head lice?

Head lice (Pediculus capitis) are small parasitic insects exquisitely adapted to living mainly on the scalp and neck hairs of their human hosts. Their six impressive legs are elegantly evolved to grasp hair shafts, and provide a striking example...

What are body lice?

Body lice (Pediculus humanus) are closely related to head lice, but are far less frequently encountered in North America. As the name implies, body lice almost always feed on thebody. They usually reside on shirts and other clothing nearest the ...

What are pubic lice?

Pubic lice (Pthirus pubis) have a short crab-like body easily distinguished from that of head and body lice. Pubic lice are most frequently found on hair around the pubic region of the infested person, but may also be found elsewhere on the body...

What about non-human lice?

Non-human lice frequent many other kinds of animals. Lice are specific as to the kind of hosts on which they will reside and feed. Just as human lice solely infest people, lice of other animals infest their specific kinds of hosts. Hence, dog lic...

What are book, bark, beggar's and sea lice?

Book, bark, beggar’s and sea ‘lice’ are each quite unrelated to lice that infest or bite people and other animals. Book and bark lice are insects commonly found in organic material such as leaf litter, under tree bark, and often within the pages ...

What about cryptic or 'imagined' infestations?

Some people earnestly believe that they are actively infested, even though no louse or other parasite can be detected. These cases can be particularly difficult to investigate and to manage. The affected individual should not be dismissed as bein...

Do head lice cause harm?

Head lice rarely cause direct harm, and they are not known to transmit infectious agents. Thus, they should not be considered as a medical or a public health problem. Head lice may occasionally be burdensome because of annoyance; their movements ...

Why were my children sent home from school?

The no-nits policies, variously drafted and adopted by school administrations, are supposedly designed to reduce the transmission of lice by excluding infested children from school. Whereas these policies may be meritorious in principle, they are...

From whom did my child acquire head lice?

Head lice are acquired from other infested people. Upon learning of their child's infestation, parents frequently seek to ascribe blame. This 'knee-jerk' reaction is understandable but unproductive. The offending lice came from some other person,...

What is the origin of head lice?

Human lice likely co-evolved with people. Our primate relatives harbor their own species of lice. Recent evidence is suggestive that body (clothing) lice evolved from head lice. The timing of this change is quite controversial. Whereas certain ex...

How many people are infested with head lice?

Head lice infest many fewer people in North America than might be believed by the general public or the medical community. In general, one should expect about one infested child in a school group of 100 children in the kindergarten through 4th gr...

What methods can I use to treat head lice?

Most importantly, ensure that a correct diagnosis/identification has been made before considering any treatment options. An old infestation, manifested solely by hatched eggs, is not a cause for treatment. Treatment should be considered only when...

Should everyone in the home be treated?

Only those with live (crawling) lice or viable eggs should be treated. Each person (adults as well as children) within the home should be carefully inspected to determine if live lice are present. All those found to be infested should be treated ...

Are head lice resistant to insecticides?

For more than a decade, parents and health care providers have increasingly reported 'treatment failures' following applications of louse shampoos (pediculicides). In many cases, many such ‘treatment failures’ may be explained because of: Misd...

Do insecticides cause resistance?

Insecticides generally do not cause mutations leading to insecticidal resistance. Rather, any insect (or any organism) may, by chance, have or develop the capacity to avoid, detoxify or eliminate toxins from its body. These few individuals may su...

Will mechanical removal work?

Mechanically removing lice and nits can be an effective method, but it is time consuming and often fails to eliminate an infestation. Because most eggs present will likely be non-viable, their removal is often impractical. Head lice and their egg...

What about nit-picking services?

Increasingly, small businesses have opened across the country to provide louse-combing and nit-picking services. Generally, these companies (or individuals) seem neither to be qualified as medical providers (yet many of them apparently render ‘di...

What about pyrethroid insecticides?

Infestations of head lice may be treated with shampoos containing permethrin or pyrethrins specifically labeled for use on people. Some formulations also contain a synergist, a chemical that may enhance the activity of the insecticide. As with an...

What about non-pyrethroid insecticides?

Other insecticides are regionally available for use against head lice, but these should be avoided unless they are contained within formulated pediculicides that are approved by the FDA and are prescribed by a physician. Generally, prescription f...

What about essential oils?

Numerous ‘home recipes’ and commercial preparations are based on mixtures of essential oils, salts or other ‘natural’ substances. Data are lacking to support the claims of their efficacy. Several formulations include substances that should not be...

What about enzyme treatments?

The chemical structure of the ‘cement’ that binds the egg to the hair is not well defined. Nonetheless, it is an exceptionally stable substance that resists degradation by diverse chemicals. Several commercial products are advertised to ‘dissolve...

What about antibiotics?

The guts of human lice contain a specialized organ that harbors an unusual type of bacteria. These bacteria may aid the louse in digesting the blood meal or by providing essential nutrients. Certain antibiotics may affect or eliminate these bacte...

What about anti-parasitic drugs?

Diverse antiparasitic agents have been proposed for treating human lice, but few have been evaluated critically. The drug ivermectin, for example, is widely used in veterinary medicine as an antiparasitic agent, and has been available for human u...

What about suffocating agents?

An increasingly popular ‘alternative’ treatment involves the use of food-grade oils, hair gels and other products in attempts to smother lice on the scalp. Certain silicone-like oils (dimethicone or dimeticone) are formulated into products market...

What about using heat?

Lice can be killed by sufficient application of heat and by the drying conditions that result from certain heated devices. The hot dry air produced by standard hand-held hair dryers may suffice to kill lice and their eggs on a person's hair. Hair...

What about freezing?

Because head lice and their eggs would only rarely be on inanimate objects, there would be little reason to treat such items. Nonetheless, freezing can kill lice and their eggs.

What about hair cuts to stop the spread of lice?

Lice will find little to grasp on a bald scalp, and competitive swimmers who shave their heads need not be concerned about head lice. Many parents and children may find this old-fashioned method to be aesthetically unappealing. Short hair is more...

What about using hair soap, bleaches or dyes?

Washing the hair each day may dislodge a few active lice; the remaining lice and eggs will be unaffected (but clean). Although hair bleaches and dyes are meant for use on the scalp, they can be caustic. Data is lacking to assess the efficacy of t...

Do dogs and/or cats serve to maintain or transfer head lice?

Pets are of no significance in maintaining or transmitting human lice, and they should not be treated for head lice.

Should I clean my house and car to eliminate lice?

Head lice and their eggs soon perish if separated from their human host. Detached lice survive just a day or so, and the eggs generally lose viability within a week. The chances of a live head louse or egg becoming reunited with a person would se...

What should be cleaned?

Head lice are acquired mainly by direct head-to-head contact with an infested person. Inanimate objects (such as combs, brushes, hair accessories and other such items) serve little, if any role in the transmission of head lice. Louse combs used ...

Should I use insecticides in the house?

Insecticidal treatments targeted at head lice within the home, school, in vehicles, or to carpets and furniture are generally unwarranted, and they unnecessarily expose occupants to insecticidal residues. Any louse that falls from a person’s hair...

Can anything repel lice?

The application of any substance to the hair with an expectation of repelling lice is unwarranted and may neither necessarily be safe nor effective. Head lice do not seem to be readily acquired naturally, and they may pose less risk than any ‘rep...

How can I have lice specimens evaluated?

Health care professionals, consumers and others can send IdentifyUS samples to confirm the identity of suspected lice and eggs. Patients are encouraged to first approach their doctor or nurse for assistance and to discuss treatment. Submitted sam...