Pediculicides (Anti-louse products)

Despite the large number of pediculicides sold in the pharmacies and the prodigious efforts of parents, successful control of louse infestation in the country remains unattainable. The high prevalence of head lice is due to a variety of reason, but the most important being that there are many ineffective pediculicides in the pharmacies, which when used according to the instructions do not eliminate the entire population of lice on the head of an infected person. Giving the impression to some parents who found living lice after some days, that they were re-infested. In some of the remedies it is recommended to apply the second treatment 7 days after the first one, which would miss several unhatched eggs (see below), while in some anti-louse product there are unclear instructions, such as applying for 15 min to 8 hrs, or repeating a treatment if “necessary”. The shampoo formulations could become less effective if they are highly diluted with water, while short application times (e.g., 2-3 min) are too short to be effective.

Although most louse eggs (69.7%) hatch on day 6 and 7 after oviposition, 27.4% of them hatch on day 8, 2.8% on day 9 and 0.1% on day 10. Though many companies recommend that a second treatment should be done 7 days after the first one, applying the second treatment on day 9-10 is much more effective. During these 10 days the chances that a new general of females will arise, that they will copulate with males and start after 24-48 hrs to oviposit, is improbable (19, 20).

While using an anti-louse product read carefully the instructions for use and note the starting time of the treatment, and rinse the product after the recommended time-period. An alarm clock could be useful to remind when the treatment should be stopped. It is recommended rinsing all topical pediculicides from the hair over a sink, rather than in the shower or bath to limit skin exposure.

Most of the pediculicides in the market were apparently never tested clinically and found to be effective. At least there are no publications which show the opposite. The Ministry of Health should demand proofs from companies that their products are safe and effective (for review see reference no. 29).

In 2016, all pediculicides based on pyrethrins, pyrethroids, malathion and carbaryl has been banned from the Israeli market. Instead, physically acting preparations based on dimethicone, octanediol and isopropyl myristate were introduced to the pharmacies. Dimethicone is physiologically inert and non-toxic, and the topical use in humans is considered safe. Today, sprays, gels, and lotion formulations of dimethicone are sold in the market with exposure times lasting usually between 15 min and 8 hrs. In most of these formulations a second treatment after 8-10 days is necessary. Some of them are also fully ovicidal so a single treatment would be enough to eliminate the head louse population on the head of an infected individual. Clinical trials were conducted and showed that some of them are effective and do not cause any significant side-effects (21, 22, 23, 24, 25). This said, introducing a new product based on the same active ingredient, does little say about its efficacy. Creating a new formulation, using different dosages and using for different exposure times, could give very different results. Therefore, each formulation should be tested separately in at least one well-designed clinical study. Because of the emergence and spread of lice that are insensitive (resistant) to the active ingredient, existing pediculicides should be re-evaluated periodically to document the actual level of efficacy they elicit.

All pediculicides in Israel are sold over-the-counter, some of which are sold through the pharmacies of health insurance companies and are cheaper.

Only anti-louse products, which have been specifically approved by the health authorities, as killing lice and eggs, should be used. It is necessary to carefully read and follow the instructions for use. It is particularly important to note the starting time and to treat the hair for the exact period specified in the instructions.

“Natural” product, which do not have a permission to claim that they do kill lice and eggs, e.g., those which claim to be effective for “hair hygiene” or pretend to be “lice-cleaner”, “nit-loosener”, or those which “treat unpleasant scalp conditions”, should be avoided.

In cases where a member of the family is found to be infested, all other family members (especially young children and mothers) should be thoroughly examined, but only those infested should be treated.  The treatments should take place concurrently on the same day if possible.

If no living lice are found, the treatment could be considered as successful even if nits are still visible on the scalp. Independently of the pediculicide used, at the end of a treatment, the scalp should be examined from time to time up to 10 days to verify that no living lice remained on the scalp. If living lice are still present, the treatment should be continued, but an anti-louse remedy with a different active ingredient or killing mechanism should be used.

Overall, 15-20% of examined children who were actually not infested with head lice but had signs of previous infestations (dead or empty eggs=nits), the nits on their hair were 2–5 cm away from the scalp, indicating that there were infested 2–5 months earlier, in the meantime were treated successfully, but the nits still remained attached on the hair. Accordingly, when the diagnosis of head louse infestation is based solely on the presence of nits, 1–2 out of 3 children are misdiagnosed as being infested and will be treated without any justification (see also H. Diagnosis).

Treating dead eggs and empty eggshells with pediculicides is superfluous, and a pediculicidal treatment will not remove or dissolve nits from the hair. Accordingly, no change in the clinical picture seen in presumable infested children (nits will be still visible on the hair) can be expected. The continued presence of nits must neither be interpreted as treatment failure, nor should it be the basis for additional treatments (on how to remove/detach nits from the hair see K. Nits and Nit Removal Remedies).

Pediculicides should be kept out of reach of children, and if they get onto the eyes, they should be immediately flushed away. While using partially used pediculicides for a new treatment, check the date which shows until when the product could be used.

If you do not know what exactly to buy, and you cannot get any information from family and friends who used an anti-louse product and were satisfied, ask your pharmacist to recommend you an anti-louse product, but feel free to let him know in case that you did not get satisfactory results, especially if you used it according to the instructions of the manufacturer.


Louse combs

There are many plastic and metal louse combs in the market, whose efficacy was either never tested or never compared with other combs. Their efficacy and their convenience to comp without tearing the hair and causing pain should be different according to the length (short, medium and long) and structure (straight, wavy, curly, and frizzy) of the hair.  Therefore, each family/person should find the comb which is best suited for his/her hair.

A louse comb as a treatment modality could be used if the hair is combed daily or every second day for 14 days. This period of time is important as lice hatch from the eggs up to 10 days after oviposition and accordingly, the combing should last first for this period, with the condition that all females were removed after the first combings. Therefore, and to be sure that all lice hatching from the eggs were eliminated, the removal of lice with the comb should continue for additional 3-4 days, or until no more living lice can be removed from the scalp for 2-3 consecutive examinations (28). This treatment modality is especially effective for short and medium length hair and for individuals with straight or wavy hair. Combing the hair after wetting (wet combing), especially after shampooing, or better, after use of a conditioner, makes combing and removal of lice and nits easier (26, 27).

In any case, the use of a louse comb should be an integral part of any anti-louse control strategy.

It is recommended to use a louse comb for each child and to kill eventually stacked lice between the teeth of the comb, by soaking them in hot water.


Hot air

Hot-air blowers such as the LouseBuster are medical devices designed to kill all life stages of head lice by delivering precisely controlled, heated air. Such a device can be used efficaciously by trained operators and could be used for everyone above the age of four. A 30-minute treatment destroys 98% of the eggs and 80% of the lice and accordingly should be used at least a second time.

Treatment modalities which should be avoided

–  Use of pediculicides for prophylactic purposes

– Use of more than one pediculicide at the same time

– Use of gasoline (with or without a combination of oil and vinegar), which could lead to neurotoxic symptoms in treated individuals

– Use of insecticidal sprays which are targeting insects in the environment, such as ants, cockroaches and mosquitoes

– Use of insecticidal sprays on beds, sofas and carpets to prevent infestation or re-infestation

– Use of food-grade oils such as margarine, Vaseline, butter, and cooking oils as they are not effective remedies and create problems to the treated individuals during and after the treatment

– Use of antibiotics unless for the treatment of secondary infections

– A short-cut of the child’s hair to prevent a re-infestation, which can cause serious problems to the child, especially to girls

A. Human lice
B. History
C. Morphology
D. Biology
E. Epidemiology
F. Clinical picture
G. Psychological effects
H. Diagnosis
I. Treatment
J. Prevention
K. Nits and nit removal remedies
L. The role of parents
M. Myths and misconceptions
N. Legal concerns
O. General recommendations
P. References