Are You Confident of the Diagnosis?

Pediculosis refers to infection with head lice (Pediculus humanus capitis or Pediculus capitis), but the condition is also known as lousiness. Infection with pubic lice (Phthirus pubis) is known as phthiriasis or crabs.

What you should be alert for in the history

Many head lice infestations cause no symptoms, and probably less than half cause itch. So you have to LOOK to find out if the patient has head lice. Do not rely on itching and scratching.

Diagnosis needs to distinguish between inactive and active infections. Active infection is the presence of live lice or live eggs. Inactive infection is the presence only of hatched or dead eggs. There are three ways of detecting an active infection:

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  • Observation of pruritus caused by lice bites on the back of the neck, postauricular areas and the scalp. Using clinical signs has a low sensitivity and specificity.

  • Observation of climbing life stages

  • Observation of live eggs

Characteristic findings on physical examination


Clinical findings in pediculosis are differentiated into primary and secondary signs.


Following a bite wheals may occur, but infected patients commonly present with pruritic papules of 2 to 3mm in diameter that may be surrounded by an erythema. Itching may or may not be a sign and less than half of patients usually present with itch. These signs indicate bite reactions and are commonly found on the back of the neck, on postauricular areas and are distributed randomly over the scalp.

In primary infections, these signs develop with a delay of 4 to 6 weeks, but in reinfections the signs appear within 24 to 48 hours. This indicates an immune-mediated response to head lice saliva, which may be a delayed-type hypersensitivity reaction similar to those seen in other ectoparasite infections like scabies.

Secondary signs develop as a result of extensive scalp scratching. If excoriation has been severe, patients may present with a history of secondary infection. This may help to confirm the presence of an older infestation. Itching and scratching may be associated with secondary infection and are unreliable indicators of pediculosis. Ulcers may develop if the patient continues scratching and is not treated. Infections such as scalp impetigo and local adenopathy should be excluded and treated, if present.

In rural Brazil, bacterial superinfection was diagnosed in 3% of pediculosis patients. In urban areas of France and Germany the rate was one percent or less. Persistent superinfection leads to the development of regional lymphadenopathy and repeated group A streptococci infections, which are a risk factor for post-streptococcal glomerulonephritis. In two populations with persistent pediculosis and limited health care access, 12% and 15% cervical lymphadenopathy was observed, respectively.

In another population with a high level of transmission, lymphadenopathy occurred in 7.3% of children with pediculosis compared with 5.5% in noninfected children. In Israel, lymphadenopathy frequency in infected children was 60% compared with 54% in uninfected children.

Lice-induced eczema on the neck and scalp may be caused by long-term chronic pediculosis accompanied by routine scratching. Lymphadenopathy in the posterior auricular and cervical nodes is not uncommon.

Rarely, a patient will present with a tangled malodorous mass of hair that contains exudates, nits, lice and possibly fungi (plica polonica). This occurs in heavily infected individuals who are incapable of maintaining basic hygiene.

Climbers (nymphs and adults)

Finding live nymphs or adult lice can be difficult since these climbing life stages move away quickly from disturbances in the hair, and they are very difficult to see. Their pigmentation varies by country according to the predominant skin color. Thus lice in Africa tend to be darker than lice in Western countries. Lice live in the hair not on the scalp so searching the scalp for climbers is rarely productive except when the infestation is heavy.

Even when the entire scalp is visually inspected an experienced assessor may fail to find live climbing head lice. In one study, visual inspection found 6% of a population positive while 25% were found positive by combing. Results from three studies have found the sensitivity of visual inspection to range from 22% to 33% as compared with wet combing, which is the gold standard (sensitivity, 99.3%).

The makers of Woods Lights, which emit a high power ultraviolet light, claim that “head lice and their nits fluoresce under black light”; however, the authors have not found this to be the case.


Eggs are not difficult to see; use a strong light and look on the hair shafts. Newly laid eggs are usually within 1.5cm of the scalp while older eggs are higher up the hair shafts. If you are not sure whether an object you find is a head louse egg, try sliding it up the hair shaft using your fingers. Eggs are usually securely attached and are quite difficult to move. Hair muffs, hair casts and dried hairspray separate easily and slide easily on the hair shaft.

Being able to identify the state of the egg is important. Hatched and dead eggs are historical evidence of infection, but are not an infection risk. A child who has hatched or dead eggs only, and no live eggs or no climbers, does not have an active infection. No treatment is needed for inactive pediculosis.

The state of the egg may be determined by checking the following:

-The shape in profile: Hatched eggs have no operculum and look like a boiled egg with the top cut off.

-The overall shape: Dead eggs collapse in on themselves and the sides are crumpled.

-The color: Live eggs are brown; hatched eggs are pale; dead eggs are brown.

-The pressure inside the egg: Live eggs “pop” when squashed between the nails; dead eggs and hatched eggs do not.

-The complete egg consists of a tube that encircles the hair shaft with the egg attached to the distal end away from the scalp. The operculum forms a lid on the top of the egg that opens upon hatching.

Live eggs have curved walls with the operculum in place (Figure 1). Dead eggs have the operculum in place, but the sides of the egg have collapsed inwards (Figure 2). Probably a live embryo is needed to maintain pressure in the egg, and when the embryo dies pressure falls and the atmospheric pressure forces the walls in. Hatched eggs have lost the operculum and have a flat top in profile (Figure 3).

Figure 1.

Live egg

Figure 2.

Dead egg

Figure 3.

Hatched egg

Live eggs = active infection and an infection risk

Dead eggs only = inactive infection; no infection risk

Hatched eggs only = inactive infection; no infection risk

Diagnosis confirmation

In clinical practice, it is difficult to confirm that a patient has active pediculosis. This is because most patients will have less than 10 climbers and it is difficult to differentiate between egg states. Diagnostic techniques, such as the conditioner and nit combing technique below, require practice and are time-consuming.

Combing using the conditioner and nit comb technique is the gold standard for finding climbers since it has high sensitivity and specificity:

  • Apply conditioner to dry hair aiming to cover each hair from root to tip with a layer of conditioner. Any conditioner will suffice, but white conditioner is best; encourage use of cheap conditioner to reduce cost.

  • Detangle the hair using an ordinary comb.

  • Immediately comb the hair with a fine tooth comb. The best comb for this is the Lice Meister comb or other nit combs with cylindrical teeth. However, plastic nit combs with conditioner are also very effective for detecting climbers (Figure 4).

  • Wipe the conditioner off the fine tooth comb onto a paper tissue and look for lice and eggs (Figure 5).

  • Repeat the combing for every part of the head at least 5 times.

  • Examine the comb for lice and eggs (Figure 6, Figure 7, Figure 8)

Figure 4.

Fine-toothed metal and plastic louse combs

Figure 5.

Lice collected from a patient

Figure 6.

Dr Canyon harvesting lice in Micronesia

Figure 7.

Dessicated louse

Figure 8.

Louse grasping a hair


Pediculus humanus corporis, otherwise known as body lice, are similar to head lice, but slightly larger. Body lice live in the clothing and come down to the skin of the body to suck blood. They lay their eggs on clothing fibers rather than on strands of hair. The eggs have the same appearance as eggs of head lice, and they will be found particularly in seams. Body lice are rare in developed market economies but can be found on homeless people in the United States and Europe.

Diagnosis of body lice: Confirm diagnosis by detection of eggs and climbers in clothes. Occasionally, climbers may be found on the body.


Phthirus pubis or Pthirus pubis is an unrelated species of blood sucking lice that, like Pediculosus, only parasitizes humans. They have a more ovoid shape and tend to flatten on the skin when exposed to light. Pediculus sp are negatively phototactic and skototactic so they tend to run rapidly from light and seek close association with other objects. P pubis can be found on any body hair (pubic, trunk, legs, axilla, beard, eyelashes and rarely head), not just hair in the pubic region. In children they are usually found on the eyelashes. However, this is not evidence of sexual abuse as pubic lice are more mobile than Pediculosus. Pubic lice transferred during intercourse have been used to genetically link rape victims and perpetrators; so they should be searched for and collected in these circumstances. Eggs are laid on the hairs in sites listed above.

Diagnosis of phthiriasis: Confirm by detection of eggs and climbers. Use laboratory to assist in confirmation of species.


Delusional parasitosis

Occasionally patients present with some symptoms of pediculosis including apparent bites, irritations, itching and visual confirmation of the presence of head lice. If the presence of lice eggs or climbers cannot be confirmed, an alternative diagnosis of delusional parasitosis may be considered. Delusions of parasitosis manifest in a patient’s firm belief that he or she has pruritus due to an infestation with insects.

Patients present with no obvious cognitive impairment and no abnormal organic factors. They usually bring in containers containing ‘proof’ of their infection, which are clothing lint, skin exudates, skin flakes, hair knots or other debris. Examination under a microscope usually reveals no lice. Because patients often presented this evidence in match boxes or plastic, this presentation has been named and is called the matchbox or the Saran-wrap sign. Although an actual lice infection that causes pruritus is not involved, inspection may reveal linear erosions with crusts, prurigo nodularis, and ulcers.

Delusional parasitosis is classified as a monosymptomatic hypochondriacal psychosis and is associated with schizophrenia, obsessional states, bipolar disorder, depression, and anxiety disorders. It occurs primarily in white middle-aged or older women, although the condition has been reported in all age groups and in men.

Who is at Risk for Developing this Disease?

Head lice are ubiquitous cosmopolitan pests, and pediculosis is globally prevalent at a high level. While some researchers believe that prevalence varies among populations, gender, age groups, race and country of residence are not risk factors since head lice persist almost everywhere as the most common human ectoparasite. Variations in prevalence are more likely due to differing social norms and behavioral characteristics within a population.

However, in particular locations, there are racial variations due to the lice having physiologically adapted to the native population and being less suited to take advantage of more recent human populations. Thus in Africa, head lice are darker and are more abundant on indigenous populations than on expatriates, whereas in the United States, the opposite is true.

Age: In general, pediculosis is more common during primary school ages and in elderly populations. In countries that attempt to resolve pediculosis, infestations are more common in primary school children, but all age groups are susceptible to head lice infestation. Head lice can also be a problem in the elderly, which may indicate an immunologic susceptibility.

Gender: While it is commonly thought that girls have a higher prevalence of infestation due to playing with each other more closely than age-matched boys, evidence suggests otherwise. Gender was reviewed by Burgess in 1995 and was found to be of limited significance, if any. Some studies found slightly more females with lice, but this was attributed to their behavior being more social rather than any genetic or physiologic factor. In a retrospective study by the authors of 136 high school students with a history of head lice, gender was not a risk factor with 53.8% males and 46.2% females.

Hair: Some researchers have found hair length to be correlated with infection, but others have not been able to confirm this relationship. In an Israeli study, boys with medium length hair and girls with short hair experienced the most lice infestation. The same study reported that brown and red hair were infested more than black or blond hair. In the author’s retrospective study, hair thickness varied (thin 17.4%, medium 49.2%, thick 33.3%), color varied (blond 16.7%, brown 67%, black 16.7%), and length varied (short 45.7%, shoulder length 27.9%, long 26.4%). These factors were not dissimilar from distributions in the uninfected population so hair is not an obvious risk factor.

Season and travel: The occurrence of pediculosis is not always correlated with seasonal fluctuation when compared between countries. However, increasing pediculosis complaints are more common in summer in the both southern and northern hemispheres. Whether this is due to temperature or changes in social circumstances that increase interaction has not been determined. Most head lice specialists who interact with the public find that pediculosis is lower during school holidays followed by outbreaks when children return to school. In Germany, pediculicide sales doubled following school holidays.

Increased travel during summer holidays increases the likelihood of head lice dissemination in different geographic areas. It is possible that these infections might be left untreated until returning home. Whether or not the weather is a significant risk factor is, as yet, undetermined, but the possibility exists that risk may be associated with climatic, environmental, behavioral and cultural factors, besides the pattern of school holidays.

Socioeconomic status: An inverse relationship exists between pediculosis and socioeconomic status, which means that people of lower socio-economic status are more likely to have pediculosis. This is most likely related to the ability to afford treatment.

Hygiene: Cleanliness is not a risk factor for pediculosis, and researchers have found that washing hair only produces cleaner lice. However, a lack of hygiene may predispose a patient to secondary infection.

What is the Cause of the Disease?

Physical factors

The lack of evidence-based data and abundance of unsubstantiated observations have led to epidemiologic studies in different geographic regions arriving at varying conclusions as to the primary mode of head lice transmission. However, a comprehensive understanding of the biology and ecology of P capitis and the epidemiology of pediculosis conclusively indicates that head lice may be acquired by different means, but that the primary route is via head-to-head transmission.

The acquisition of head lice from fomites and the environment is considered to be an uncommon event. The in vitro studies that have investigated fomite-to-head transmission are faulty, and field studies have demonstrated convincingly that several likely fomite candidates are inconsequential or of no importance as causes of infection.

Social factors

The transmission of head lice is governed by many interrelated variables, but physical factors have been the focus of most research to date. However, research on social aspects of pediculosis indicate that physical factors are less important than social and behavioral factors. Historically, social interaction, the primary mode of infection, was the only social factor considered, but new causes and risk factors have come to light.

The authors recent research has found a high degree of apathy and neglect in those that have pediculosis and in their care-givers. This is the primary cause of reinfection since untreated people act as reservoirs to re-disseminate head lice into treated populations. It is also surmised to be the reason why large control programs do not work, even if there is no decrease in susceptibility of the head lice population to the pediculicide employed.

Thus, the control of head lice should focus on the head, not on the environment, and schools and other institutions wishing to be proactive should invest their resources into educational approaches if they wish to render their mass treatment campaigns more effective.


Human lice belong to the phylum Arthropoda, the class Insecta, the order Phthiraptera, and the suborder Anoplura (blood sucking parasites of mammals). Anoplura contains 15 families and 47 genera. Two thirds of these are specific parasites on rodents. Virtually all are very host specific. Medically important genera are Pediculus humanus (body louse), P capitis (head louse), and Pthirus pubis (crab louse).

Anoplura lice are small insects (average 2mm; range 0.5 to 8mm long). The eyes are comparatively well developed in human lice, there are no occeli, no palps and the antennae are reduced in size. P capitis possess small anterior mouthparts with hooklets that aid their attachment to the host while feeding. These mouthparts retract into the head when lice are not feeding. Lice are thought to require several blood feeds a day for a few minutes each time. The female louse cannot survive for more than 3 days without a blood meal.

On each of the six legs, there is a single tarsal segment with a single claw that can be adjusted to either climb up and down hairs or to crawl along the scalp. When the tarsal claw is retracted it connects with an opposing immovable claw creating a space the size of a human hair. P capitis have no wings and cannot jump but they are able to move on a hair shaft at a speed of 23cm per min. Movement on smooth synthetic surfaces is limited.

P capitis bodies are flat and covered with a chitin exoskeleton. The dorsoventrally flattened thoracic segments are fused, and there are nine abdominal segments. Breathing spiracle pairs are present on each of six abdominal segments and on the mesothorax. Males have a rounded abdomen end with prominent ventral genitalia. In females, the abdominal ends are bi-lobed. Females are larger than males.

Eggs are laid at the base of the hair shaft, within 2mm of the scalp. Preferred oviposition sites are the posterior hairline and postauricular areas. The process of laying down the cement attachment tube and subsequent oviposition takes 16 seconds. The eggs hatch in 7 to 10 days, and there are 3 instars, which take 8 to 10 days to develop. The mature female adult lives around 34±13 days and after a preoviposition period of 24 to36h, can lay 270 to 300 eggs in a lifetime (9 to 10 eggs per day).

Infestations can build up quickly. In the absence of limiting factors (ie, in a controlled environment) lice can increase their population size by 31 times per generation with the population doubling every 6 days. Even in a controlled environment, death commonly occurs from gut rupture into the hemocoel during feeding or cementing of the female to the hair shaft during ovipositioning.

Systemic Implications and Complications

Anemia from blood loss due to head lice infestation is possible and has been documented in patients with persistent pediculosis with hundreds of head lice. Head lice on the average patient with a case of active pediculosis would imbibe 0.008mL of blood per day. The loss of this quantity of blood is not clinically significant even in iron-deficient children.

However, blood loss in the most heavily infected child observed in the literature, who harbored 2657 lice, would be 0.7mL/day or 20.8mL/month. This may be of clinical importance in a child on an inadequate diet, and would be significant in an iron-deficient child. These figures are based on the expectation that a head louse will feed only 3 times per day. If this figure was higher, say 6 times, the risk of anemia would increase and a heavy infestation would have greater potential to cause systemic iron deficiency.

P capitis has been shown to be sufficiently competent in laboratory settings to become a vector for epidemic typhus caused by Rickettsia prowazekii and relapsing fever caused by Borrelia recurrentis. However, there are no known instances of head lice transmitting these pathogens outside of the laboratory setting.

Treatment Options

If head lice are found, the patient should be treated. If the patient has not been treated for head lice before and live eggs are found, you should recommend treating for head lice. If in doubt or if the patient does not want to use insecticidal treatments, check again the next day using the conditioner and comb technique described above.

If the patient has been treated recently, and you find only hatched eggs, but no lice, you may not need to recommend treatment since the eggs could be from an old infection. Recommend that the patient check themselves every week using conditioner, a fine tooth comb, and paper tissue, as described above, until no signs are found.

How is pediculosis treated?

Head lice live in the hair and come down to the scalp to feed by sucking blood. Thus, to be effective, head lice formulations must be applied to all parts of the hair. A complete regime consists of two treatments 7 days apart. The first kills the climbers, and the second kills the juvenile lice hatched from the eggs over the intervening 6 days. No product currently available kills all eggs regardless of product claims.

Apply the product to all areas of the head and coat all hairs from roots to tips. If you are using lotions, apply the product to dry hair. For shampoos, wet the hair, but use the least amount of water possible. For long hair apply the treatment formulation near the scalp and then use an ordinary comb to carry the formulation down the hair shaft to the tip. If the product is left on the comb after one sweep, it should be wiped onto the same or a new area of hair at the base and the process repeated. By repeating this process several times for hair all over the head, one can obtain an even coverage of all hairs from roots to tip. In addition the hair is tangle free and use of a fine tooth comb is subsequently simplified (Figure 9).

Figure 9.

Applying treatment

When the hair has been totally covered, the hair needs to be left for a period of time, usually at least 20 minutes. But each product has its own specifications. To enhance exposure to the volatiles, the head may be wrapped in cellophane during this exposure period. Care needs to be taken to avoid getting product on clothing and in eyes or ears.

How to assess product effectiveness and possible insecticide resistance?

If a head lice product works, lice will be dead within 20 minutes. After the exposure period, you can test if the lice are killed by using a fine tooth comb to comb the hair. After each sweep from roots to tip, wipe the combings onto a tissue. Repeat this many times until the whole head has been combed at least twice and little treatment formulation is visible on the hair. Rinse the lice in a tea strainer and wait for 30 minutes. This is done because lice go into stasis during treatment and may appear dead when in fact they are not.

Then examine the lice to see if they are alive or dead. A magnifying lens is not needed to do this but will help in the visually impaired. Grade each louse as dead if you see no movement, inactive but alive if it is stationary but is moving legs or antennae, or active if it is crawling.

–If all lice are dead, the lice are sensitive to product used, which is effective.

–If some lice are inactive but alive, they may be partly resistant to treatment. However, if no lice are active, the louse population is considered “sensitive.”

–If some lice are active, they are resistant and the product has failed.

For a sensitive population of head lice, the current treatment has been successful, but embryos in eggs will most likely survive. Retreat in 7 days using the same product. For resistant lice, the current treatment has been unsuccessful. Wash off the first product. Retreat as soon as possible using a product from a different active group than the one used. Although there are over 20 head lice products (Figure 10), they fall into several groups based on the active compound:

Figure 10.

Great variety of treatments


–Pyrethroids (permethrin and bioallethrin)

–Organophosphates (malathion or maldison)

–Organochlorines (lindane—banned in most countries)

–Benzyl benzoate (used in some products, mostly as an antiparasitic acaricide, miticide and scabicide)



Pyrethrin is the most popular natural bioinsecticide and originates from Chrysanthemum cinerariifolium and C coccineum flowers. Randomized comparative clinical trials have concluded that it is effective against susceptible lice.


Avermectins, such as ivermectin, derive from the bacterium Streptomyces avermitilis and act as broad-spectrum antiparasitic and antihelminthic agents. Orally and topically, ivermectin is effective against blood-sucking arthropods; however, it is not registered as a pediculicide in most countries.


Spinosad derives from the soil bacterium Saccharopolyspora spinosa and is a new chemical class of insecticide registered by the US Environmental Protection Agency. In January 2011, the US Food and Drug Administration approved Natroba (spinosad) Topical Suspension 0.9% for the treatment of head lice infestation in patients ages 4 years and older.

–Herbal mixtures and oils

Most herbal mixtures will cause a “knock-down” effect in lice in which they go into a condition of stasis. However, they often recover from this and resume their normal parasitic activities. Some ‘”natural” bioinsecticides deserve mention:

Tea tree oil, steam-extracted from Melaleuca alternifolia bushes, is less effective than pyrethrin but may be used against susceptible lice in a 4% to 10% solution.

Neem oil, press-extracted from Azadirachta indica seeds, has toxic effects on insects, but results are mixed and any toxicant that does not induce 100% mortality is not worth using.

An infusion or tincture of Quassia amara is reputed to cure lice but no clinical study has confirmed this promising bioinsecticide.

If the product does not kill lice, look to see what the active compound is and then choose a product from another group. Apply the product and reassess using steps above in the treatment schedule.

Is a second treatment necessary?

Yes, in almost all cases a second treatment is needed since no head lice treatment kills 100% of the eggs. So if the first treatment kills all climbers, at the second treatment one would expect only juveniles, hatched from eggs during the 7-day period, and no adults. If adults are present, reinfestation has occurred. You must retreat on day 7 with the same product that worked on the first treatment. Evaluate efficacy using the same protocol. If lice are found at the second treatment, and they are killed by this treatment, there are two options:

  • Retreatment with same preparation a third time in another 7 days to verify complete cure, or

  • Seven days after the second treatment, put conditioner in the hair, comb with a fine tooth comb and check for lice

The choice of option depends on the patient’s philosophy. Option 1 is selected to make sure all lice are killed, and option 2 to minimize exposure to insecticides. If treatment has been as successful as possible, only juvenile lice should be found at the second treatment, and no lice should be found on the third treatment or the third examination. If no lice are found at the second treatment, the case has been cured.

Protocol for failed treatments

To manage treatment failures in pediculosis, systematically look at the potential causes of failed treatment. Use the following check list in a step-wise fashion.

  • Is the product being applied correctly? (Cause 1 below under Optimal Therapeutic Approach).

  • Are the head lice sensitive to the product being used? (Cause 2).

  • Has a complete treatment regime of at least two applications been given? (Cause 3).

  • Is reinfection occurring? (Cause 4).

Treatment failures can be due to several causes, but the ones lower down the sequence can not be accurately identified until the ones higher up have been corrected.

Caregivers should be systematic and should not expect a cure in less than 1 week. Pediculosis is a minor disease, so advise the caregiver not to use measures that put a child’s health at greater risk.

Are head lice treatments safe?

All head lice products contain insecticides and most work by attacking the nervous system of the lice. In most countries, all products are required to be licensed and registered with the relevant national drug safety registration authority. Some chemical treatments are not globally available. For instance, lindane, an organochlorine, is available in the United States and carbaryl is available in the UK by prescription, but these chemicals are banned in many other countries. The chronic toxicities of the active ingredients are less well recognized. The aim should be to keep exposure to insecticides to the minimum required to eradicate head lice.

Check to see that the product is licensed for use in your country. If the product does not have a registration or license number it may be marketed legally under other legislation, or it may be being sold as a head lice product without official approval. Be wary of head lice treatment products that are not officially approved. Herbal products may contain equally toxic compounds, but they are not regulated in most countries.

Excoriation and lice-induced eczema render patients susceptible to alternate exposure routes, which considerably increase the absorption of pediculicide. This is of particular importance when neurotoxic compounds are applied topically. The persistent use of chemical treatments to control resistant or recurrent infections is not advisable and patients should be advised to switch to non-chemical treatments, such as using conditioner and a fine-toothed comb.

Cleaning as a preventive measure is ineffective

Head lice occasionally find themselves off the human scalp but they are likely to die if they leave the head. The only way head lice can get water and food is by sucking blood from the scalp. A head louse not on the head is a head louse in a desperate situation! Head lice will dehydrate when off the head. The rate at which this occurs depends on the amount of water vapor in the air. In an air-conditioned room, head lice will be severely dehydrated after a few hours. When it is wet and raining, head lice may live for 24 hours.

Previously described studies of classroom floors and school hats found no evidence that lice exist off the human head. Cleaning the environment, beds, floors, etc is thus a complete waste of time and effort.

“Natural” therapies

Natural products are often sought because they are considered safer than synthetic chemicals. However, many natural pediculicides employ similar neurotoxic mechanisms to synthetic chemicals. The safety of natural products is questionable since they are not subject to the same safety therapeutic drug regulations as synthetic chemicals. The claims of efficacy are also not subject to the same level of scrutiny and many are unsubstantiated. Some biocidal products, such as lice-blaster, have proven efficacy, but most have limited efficacy.

Repellents: There are many so-called repellents on the market, but none of them is effective in preventing the transmission of head lice.

Hair cutting

In desperation, some patients have their heads shaven to be sure to rid themselves of head lice. While this is totally effective, it is an extreme measure and is not socially acceptable in some cultures. Cutting the hair very short (< 1cm) will make it easier to implement head lice treatments and certainly facilitates fine-tooth combing. Hair lengths above 2cm are able to conceal significant populations of head lice.


Any of the above-mentioned head lice products may be used to treat the human body for body lice. Clothes and all materials in contact with the patient should be washed in hot water (>54 °C, 130 °F) and dried in a heated clothes dryer. Since lice must feed regularly, placing clothes and bedding in plastic bags away from blood sources for a week is a common practice. This should suffice to kill crawlers but not eggs, which will hatch and reinfect the patient.


Public lice are best treated with topical permethrin lotion of the type used for scabies.

Optimal Therapeutic Approach for this Disease

Difficult cases of failed treatment

Some cases of pediculosis seem horribly persistent. A very systematic approach is required to cure these patients. Reasons for failure come down to one or several of the following causes:

Incorrect application of the product

Lice are resistant to insecticide

Failure to retreat to kill nymphs emerged from eggs


The order of listing of these causes is very important. To determine why the pediculosis persists, you have to start at the top of the list and work to the bottom. By approaching the problem systematically, you can usually work out which aspects are significant in a particular case. Each case is different.

Cause 1. Inadequate application of product

In this problem the chemical does not come into contact with the lice for long enough at a high enough concentration. This is usually due to failure to cover all hairs adequately with the chemical. Cover from roots to tip. This problem occurs most commonly in treating pediculosis in long hair. One way of ensuring that coverage is adequate is to comb the product in with a normal comb. The end result is a head with every hair coated from root to tip, and lying parallel with its neighbors. The “parallel” aspect ensures that the product has been combed through and makes subsequent use of a fine tooth comb easier.

The product should be on the hair for 20 minutes.

Check how you are applying the product. If you meet the above criteria, then application is not a problem.

Cause 2. Lice are resistant to the insecticide used

Head lice can become resistant to insecticide. Some strains appear to be resistant to at least two insecticides simultaneously. Insecticide resistance in lice cannot be predicted before exposing them to insecticide. Resistant lice look just the same as sensitive lice. One can roughly assess insecticide resistance by treating the head adequately as described in Point 1, leaving the product on for at least 20 minutes, and then checking for live lice.

Use a fine tooth comb, and after every stroke from roots to tip wipe the combings onto paper tissue. Look for movement. If the lice are active and walking around, you have a strain that is resistant to the insecticide in that product. If they are all dead or immobile, the lice are sensitive to the insecticide. If lice are resistant, change to a product containing a different insecticide.

Key points: note the active ingredient, not the product name. If the lice are resistant, swap to another active ingredient.

Cause 3. Failure to retreat to kill nymphs newly emerged from eggs

No product kills 100% of eggs even if the strain of lice is sensitive to the active ingredient. Eggs take 7 days to hatch. Therefore, starting from 1 day after treatment to about 7 days, nymphs may be hatching to come back onto the hair. Retreatment at 7 days is a mandatory part of the initial treatment regimen. At this treatment if things are going well, you should expect to find nymphs, but no adults. At 14 days you should recheck the hair, or if necessary, retreat a third time.

Whether you retreat, depends on your philosophy. If you want to make 100% sure the lice are eradicated, you retreat using the same product. If you just want to check, use conditioner to do so or a mechanical technique like the LiceMeister comb, and retreat only if you find nymphs. The technique using conditioner is described in depth at

Cause 4. Reinfection

Reinfection can complicate treatment of head lice. This occurs usually from head-to-head contact with an infected child. Reinfection from the environment is rare.

Reinfection is hard to detect. Suspect it if you have a sensitive strain as shown by testing as described in Point 3, and are treating it correctly (Cause 1 and Cause 2), but you unexpectedly find adult lice in the hair. Check the hair weekly by using the conditioner technique, or a good metal comb like the LiceMeister comb. If the hair is clear one week, and lice are present the next, reinfection is highly likely. However, do not blame reinfection for persistence of pediculosis until you have ruled out the other causes (Causes 1 to 3).

If you suspect reinfection, ask your patient who she/he has had head-to-head contact with and see if they can be checked. Being in the same room with an infected person does not necessarily result in the transmission of head lice. Head-to-head contact is needed. The potential sources of reinfection for your patient may come down to just a few children, even in a class with a number of children with pediculosis since the patient will probably only have head-to-head contact with a few of them. Do not just concentrate on the classroom; look at head-to-head contact opportunities at play and in the family.

Patient Management

As described above, the management of head lice can be complicated. The patient must be encouraged to become proactive in seeking out an effective treatment and to follow treatment instructions carefully. Recurrent infections may be due to the four problems below and a management plan should be developed for patients in which pediculosis persists.

–Incorrect application of the product

–Lice are resistant to insecticide

–Failure to retreat to kill nymphs emerged from eggs


Unusual Clinical Scenarios to Consider in Patient Management

Unusual presentations of head lice infection and secondary infection complications have been explained in the diagnostic section.

Remember to review the material on delusional parasitosis in the section on “Conditions in the differential diagnosis that may reasonably mimic the diagnosis” because DP patients may be extremely difficult to manage.

What is the Evidence?

Burgess, IF. “Human lice and their management”. Adv Parasitol. vol. 36. 1995. pp. 271-342. (A large and substantive piece of work containing almost all there was to know of human head lice at the time.)

Canyon, DV, Speare, R. “Indirect transmission of head lice via inanimate objects”. Open Dermatol J. vol. 4. 2010. pp. 72-6. (A review of a controversy in head lice transmission research that evaluates evidence in favor of head-to-head transmission and transmission from fomites (inanimate objects). It concludes that there is little substantive evidence to support fomite transmission and that head-to-head transmission is the primary mechanism of infection.)

Canyon, D, Heukelbach, J. “Head lice repellents”. Management and control of head lice infestations. 2010. (A review of research on the use and testing of so-called head lice repellents that fairly conclusively denounces all repellents as ineffectual.)

Canyon, D, Speare, R, Heukelbach, J. “Head lice transmission and risk factors”. Management and control of head lice infestations. 2010. (An in-depth review of valid and invalid current ideas on head lice transmission. All factors that are thought to pertain to the risk of contracting head lice are discussed and dissected for scientific value.)

Canyon, D, Speare, R, Heukelbach, J, Heukelbach, J. ““Natural” treatments and home remedies”. Management and control of head lice infestations. 2010. (A systematic review of the most promising natural head lice treatments.)

Canyon, D, Speare, R, Heukelbach, J, Heukelbach, J. “Internet links and additional resources”. Management and control of head lice infestations. 2010. (A good collection of online sources of information for physicians and patients who seek medical or practical or scientific information on head lice.)

Gratz, N.G.. Human lice: their prevalence, control and resistance to insecticides: a review 1985-1997. 1997. pp. 61(A summary of head lice around the world that describes a global pandemic due largely to increasing travel but also to insecticide resistance.)

Fellner, MJ, Majeed, MH. “Tales of bugs, delusions of parasitosis, and what to do”. Clin Dermatol. vol. 27. 2009. pp. 135-8. (A practical clinical paper on delusional parasitosis containing a sound description of the signs and symptoms of the illness and medical advice.)

Falagas, ME, Matthaiou, DK, Rafailidis, PI, Panos, G, Pappas, G. “Worldwide prevalence of head lice”. Emerg Infect Dis. vol. 14. 2008. pp. 1493-4. (A synthesis of available evidence (55 prevalence studies) regarding the worldwide distribution of lice infestation in the 21st Century.)

Heukelbach, J. Management and control of head lice infestations. (The most recent and most complete text on the current state of knowledge concerning almost all aspects of head lice.)