US Pharm. 2016;41(5):8-11.

Head lice—the very thought of these parasites and the scratching begins! The head louse has been causing irritation and disgust for at least 10,000 years.1 The true prevalence of head lice infestation, or pediculosis capitis, is not known because the reporting of such cases is not mandatory. However, it is estimated that there are 6 to 12 million lice infestations occurring annually among children 3 to 11 years of age.2 In recent years, there has been a steady increase in lice infestations, most likely due to emerging treatment resistance.3 The annual cost of head lice infestations, including treatment costs, lost wages, and school system expenses, is estimated to be $1 billion.4

Head lice are not a health hazard, nor are they vectors for disease. For parents, or anyone who has been affected, these parasites are a source of great angst and are considered social and emotional nightmares. There is significant stigma associated with head lice infestation. Many view it as a sign of uncleanliness, with affected children being ostracized in school, by friends, and at social events.5 Treatment usually begins in the pharmacy with individuals seeking OTC products. Pharmacists play a pivotal role in selecting the proper product, educating about appropriate use, and reassuring patients about the condition and its resolution.


The insect that causes infestation of the head and hair is Pediculus humanus capitis—the head louse. This ectoparasite makes its home in the skin and hair of humans, feeding exclusively on human blood from the host every 4 to 6 hours.6,7 The adult head louse has a tan to grayish-white color, and measures 2 to 4 mm in length.5-7 The louse’s cylindrical shape helps it move freely among dense hair. It has three pairs of well-developed clawed legs that are used for grasping the host’s skin and hair shafts.6

The female louse has a lifespan of approximately 1 month. During this time, it can lay up to 10 eggs a day. These eggs, or nits, are firmly attached with a gluelike substance to the host’s hair shaft close to the scalp.8 The nits are incubated by the host’s body heat and typically hatch in 5 to 10 days, releasing nymphs. The nymphs begin feeding immediately, and reach adulthood after 9 to 12 days. The female can begin reproducing 1.5 days after becoming an adult. This cycle will repeat approximately every 3 weeks if the infestation is left untreated.5


Head lice are wingless parasites that crawl; they do not jump or fly from one host to another. Pets or other animals are not considered vectors.9 There is general agreement that direct head-to-head contact is the main mode of louse transmission.5,7,9,10 Indirect transmission via fomites such as clothing, hair accessories, bedding, pillows, and towels has been proposed, but data are conflicting and such transmission is much less likely to occur.5-7,10 Head lice usually survive for less than 1 day when separated from the host; off the scalp, they die quickly from starvation and dehydration.9,11 Nits cannot survive at temperatures lower than those found near the host’s scalp.11

Risk Factors

Age plays a substantial role in the occurrence of infestations, with children aged 3 to 11 years being the most likely group to become infested. This may be due to an increase in head-to-head and body contact while playing.11 Overcrowded living conditions and close contact with infected persons also increases the risk of becoming infected.6 Infestations in the United States are less common among blacks; this may be due to their oval-shaped hair shafts, which are harder for lice to grasp.12 Females are at greater risk of infection than males, possibly as a result of their social behaviors.2,11

Clinical Presentation and Detection

Although pruritus around the back and sides of the scalp is traditionally the first clinical symptom of infes-tation, patients may initially be asymptomatic, especially in a light infestation (one to five lice).6,13 Pruritus is a delayed hypersensitivity reaction to the enzymes present in the louse’s saliva, which contains vasodilatory and anticoagulant properties.5 With a patient’s first exposure, it can take up to 4 to 6 weeks for pruritus to develop; with repeat exposures pruritus will occur within 1 to 2 days.5,14 Small erythematous macules, papules, or hivelike reactions may also be present, depending on the degree of sensitization and previous exposure.11 For some patients, the pruritus can be intense, which could lead to excoriations and secondary bacterial skin infections due to the associated scratching. Patients may also describe a tickling feeling or sensation of movement on the scalp, irritability, and difficulty sleeping due to head lice being more active at night.13

In children, head lice infestation is first suspected when they begin scratching their heads vigorously. The gold standard for diagnosing head lice infestation is finding a live louse or nymph on the scalp or a viable egg in the scalp hair.8 Inspection should concentrate around the crown of the scalp, over the ears, and at the lower neck. The presence of nits is often mistakenly used as a diagnosis. It is possible for nits to remain present several days after they have hatched and months after successful treatment.13,15 In general, eggs found more than 1 cm from the scalp should not be considered viable.5

Visual inspection of the hair and scalp alone may miss almost three-fourths of all infestations; lice can camouflage themselves within the patient’s hair, avoid light, and are very quick, moving up to 9 inches per minute.5,7,9 Diagnosis using a fine-toothed louse or nit comb is more efficient, known to be four times more effective and twice as fast in detecting live lice.5,9,16 Experts have recommended wetting the hair with a lubricant (water, oil, or conditioner) to help slow the movement of the lice. After the hair is brushed to remove tangles, a fine-toothed comb with teeth 0.2 to 0.3 mm apart should be inserted near the crown of the scalp and firmly drawn down the entire length of hair. After each stroke, the comb should be inspected for live lice. The entire head should be combed systematically twice. It usually takes about 1 minute to find the first louse.16


Treatment is recommended for those with a clear diagnosis with living lice.5 Treatment goals include killing adult and nymph lice, removing nits from the hair, and controlling symptoms such as itching. When infestation has been determined, all members of the household and close contacts should be inspected. It is also important to treat any family members who share the same bed with the infected individual, even if no live lice are found.5

Pharmacologic Treatment

Pharmacologic treatment options are classified as either pediculicidal (killing nymphs and adult lice only), ovicidal (killing nits, but not affect-ing nymphs or adult lice), or both. There are currently a number of OTC and prescription therapies available for the treatment of head lice (TABLE 1).17-23

OTC Treatment

The available OTC pediculicides in the U.S. are the topical pyrethroids, which include permethrin and pyrethrins plus piperonyl butoxide. Both agents are neurotoxic to lice, causing paralysis and death, but have extremely low mammalian toxicity.5

Permethrin: Permethrin has been the most studied agent and is the least toxic to humans.5 It was approved in 1990 for OTC use and is marketed as a 1% crème rinse. No major adverse effects have been reported with its use. Minor adverse effects include rash, pruritus, pain, burning, and tingling. Compared to pyrethrins, permethrin is less allergenic and does not cause allergic reactions in individuals with plant allergies.5 The product should be applied to damp, towel-dried hair after washing with a nonconditioning shampoo. The product is left on for 10 minutes then rinsed off. Treatment should be followed by combing the hair with a fine-toothed comb.

Permethrin leaves a residue on the hair shaft that allows it to maintain activity for up to 10 days after treatment. This residue is meant to target the 20% to 30% of nymphs emerging from eggs that were not killed with the initial treatment, decreasing the need for retreatment. Conditioners and other silicone-based additives present in most shampoos impair this action by disrupting permethrin’s adherence to hair shafts, reducing this effect.5 If live lice are detected at least 7 days after the initial treatment, evidence suggests retreatment at day 9 is most beneficial.5

Pyrethrins Plus Piperonyl Butoxide: Pyrethrins are derived from chrysanthemum flowers; therefore, patients who are allergic to these plants or ragweed should avoid their use. When compared to permethrin, these products demonstrated less pediculicidal efficacy.17 Pyrethrin is combined with piperonyl butoxide, which acts synergistically by inhibiting the metabolism of pyrethrin, thereby increasing its concentration in the louse. This product is available as a shampoo and mousse. It should be applied to dry hair and left on for 10 minutes before rinsing and combing hair with a fine-toothed comb. A retreatment in 9 days, optimally, is needed to kill newly emerged nymphs from eggs that survived. The adverse effect profile is similar to permethrin and is generally well tolerated.24


The issue of head lice resistance has recently been in the spotlight. In August 2015, a press conference was held to discuss the findings of an analysis of lice samples collected from across the U.S. The findings indicated that lice in at least 25 states have developed resistance to pyrethroids.25 There are several options for use in children who may have resistant lice; however, the American Academy of Pediatrics recommends the use of permethrin 1% and pyrethrins as a reasonable first choice for primary treatment, unless resistance has been proven in the community.5

Alternative Approaches

Various other products have been used in the eradication of lice, including essential oils and occlusive agents such as petrolatum shampoos, margarine, mayonnaise, butter, and olive oil. The use of essential oils, such as tea tree and lavender oil, is not recommended, as much of the evidence available is unclear. These oils are also a source of contact irritation, leading to inflammation and allergic contact dermatitis.5 The use of occlusive agents overnight theoretically suffocates lice by blocking their spiracles, but once the agent is washed off, the lice reopen their spiracles and begin breathing.3,11

Environmental Interventions

Only items that have been used by the affected individual within the last 24 to 48 hours before treatment should be considered for cleaning.5 This is because lice are unlikely to survive beyond 48 hours off a host. Items include clothing, headgear, bedding, furniture, and carpeting. Clothing, bedding, and hats can be dry cleaned or washed or soaked in temperatures >130ºF for 20 minutes and then dried in the hot air cycle of the dryer. Combs and brushes can be soaked in hot water for 10 minutes. Furniture, carpets, car seats, and other fabrics should be vacuumed thoroughly and routinely. Keep in mind, however, that the risk of infestation from lice that have fallen from a host is very rare, and viable nits are unlikely to incubate and hatch at room temperatures.5


Pharmacists are most likely the first point of contact for patients and/or parents confronted with a lice infestation. These individuals need to be counseled on the appropriate selection and proper use of available OTC products. Many patients fail to reapply the treatment after 7 to 10 days as instructed, leading to treatment failure. If after two to three treatment applications lice are still present, patients should be referred to their healthcare provider. In addition, patients need to be educated regarding strategies to prevent future infestations. Pharmacists can help ease the social stigma related to this condition by dispelling the common myths associated with head lice.


How Does Someone Get Head Lice?

People get head lice from someone who already has them; usually the transmission is by direct head-to-head contact. It is because of this close contact that large outbreaks of lice infestation are common in places such as day care centers and schools. Head lice may also be spread by sharing items like hats and combs, but this is rare.

How Can I Tell If My Child or I Have Head Lice?

Itching is traditionally the first complaint. In children, head lice infestation is initially suspected when they begin scratching their heads vigorously. When you are first infected with lice, it may take up to 4 weeks for the itching to begin. After that, itching will usually happen 1 to 2 days after. Some people may not have any symptoms. You may see red bumps on the scalp and small, yellowish-white oval nits, or eggs, stuck to the hair. At first, they may look like dandruff, but unlike dandruff, nits do not shake off easily.

How Do I Treat Head Lice?

Treatment is only necessary if you actually see live lice in the hair. To find live lice, the best way is to use a fine-tooth comb to check all areas of the scalp.

  • First detangle the hair with a regular brush or comb. This can be done with wet or dry hair, although wet hair has shown to be better
  • Place the fine-tooth comb to the top of the head, touching the scalp, and pull the comb through the hair in 1-inch sections. After each stroke, check the comb for lice or eggs. Do this to the entire head at least twice.

If lice are found, there are a few things that can be done:

  • Continue to use the fine-tooth comb and repeat this process until all nits and lice are removed from your hair. This may take a few weeks
  • Use an OTC lice product with permethrin 1% (e.g., Nix) or pyrethrin (e.g., RID)
  • Follow the directions as written on each product. Some products may require you to repeat
    the treatment in 7 to 10 days, which is very important to do
  • If you still see lice after two treatments, call your prescriber. A prescription product may be needed.

What Can Be Done to Prevent Future Episodes?

Extensive cleaning is not necessary. The risk of infestation from lice that have fallen from someone’s head is very rare, and eggs are unlikely to hatch at room temperatures. But the following can be done to reduce the risk of getting lice again:

  • Clothing, bedding, and towels that were used in the last 2 days should be washed in hot water (at least 130ºF) and/or dried in a hot dryer for at least 20 minutes
  • Combs and brushes can be soaked in hot water for 10 minutes
  • Furniture, carpets, car seats, and other fabrics should be vacuumed
  • Lice sprays or powders are not needed
  • Continue to carefully check your child’s head for several weeks after treatment and periodically after that.

Remember, if you have questions, Consult Your Pharmacist.


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