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OTC casebook: head lice


OTC casebook: head lice

Several parents have been coming in to the Casebook Pharmacy concerned about an apparent epidemic of head lice in the local primary schools.

They have been asking the pharmacist, Eve, questions and relaying opinions that they have heard from other parents. Eve has been doing her best to offer pertinent advice and dispel misconceptions.



1.     Head lice spread from person to person by flying or jumping.

2.     How can the presence of lice be recognised?

3.     “My child won’t get lice: I keep her head scrupulously clean.”

4.     “I’ll know if my child has lice as his head will be itchy.”

5.     What treatments are available to get rid of head lice? 

6.     “Is there anything I can use to keep head lice away from my child and family?”

7.     “Is it only children who get infected with head lice?”

8.     “If I find that my child has head lice, should I treat the whole family to prevent them from getting lice as well?” 

9.     Can head lice treatments be used on babies and young children?

10.  Where can I find further information about head lice?




1.     Head lice (pediculus humanus capitis) do not fly or jump. Adult lice are black, brown or grey-white crawling insects some 2-3 mm in length. They exist only on human heads. Infection is spread by direct head-to-head contact from person to person. Transfer by any other means is highly unlikely. Lice lay their eggs at the base of hair shafts and the eggs adhere to the hair, attached with a strong glue-like substance.

2.     Live and dead head lice and yellowish cast exoskeleton shells can be seen by wet combing - combing the hair with a fine-tooth comb over a sheet of white paper after shampooing and towelling dry.

Lice faecal material may be found as black specks on pillows and collars. Creamy-coloured empty egg cases – ‘nits’ - remain firmly attached to hair shafts as they grow outwards and are a sign of previous, though not necessarily current, infection.

3.     Head lice aren’t fussy - they will live on clean or dirty hair. 

4.     Pruritus is an allergic response to lice saliva injected into the scalp to liquefy blood on which lice feed. It usually takes several weeks to develop after initial infestation and can persist for several weeks after successful treatment.

5.     There are basically two approaches to eliminating head lice: insecticidal, both chemical and physical, and mechanical. Physical insecticides are generally considered the first-line treatment.

Chemical insecticide:

Malathion. Resistance to neurotoxic chemical insecticides has increased to the point where malathion is the only one still recommended for eradication of head lice.

Permethrin crème rinse, although still marketed, is now classified in the BNF as ‘less suitable for prescribing’ for this indication.

Malathion is an organophosphorus compound, a potent cholinesterase inhibitor that prevents the breakdown of acetylcholine and interferes with neuromuscular transmission in the head louse, paralysing it and preventing it from feeding.

It is oil-soluble and absorbed by passive diffusion through the lipid coat of both insect and egg. It is poorly absorbed through human skin, and much more efficiently detoxified by human metabolic processes than by those of insects. It is therefore safe for occasional or intermittent use at low concentrations as a pediculicide.

There are no contraindications to the use of malathion apart from known sensitivity.

Malathion is available as an aqueous lotion. It is applied to dry hair and allowed to dry naturally over at least 12 hours. It is then shampooed or rinsed out and dead lice and eggs are combed out. The treatment should be repeated after 7 days.


Physical insecticides:

Dimeticone is a long-chain linear silicone and is used as a physical pediculocide. There are two types of formulation: 4 per cent dimeticone in a volatile silicone base (cyclometicone). It appears to act by coating the insects and thus disrupting their ability to breathe and to absorb and excrete water. It does not kill eggs, so a second application is recommended seven days after the first.

·       92 per cent dimeticone. At this concentration it penetrates the respiratory system of adult lice and nymphs and into the pores of eggs, causing suffocation. It is left on the hair overnight. A second application may not be necessary

Other constituents of physical pediculocides include:

Octane-1,2 diol, an alkyl diol surface active agent that appears to act by disrupting cuticular lipid on both head lice and their eggs, resulting in dehydration.

Cyclometicone/isopropyl myristate. Cyclometicone is a cyclic polydimethylsiloxane. Isopropyl myristate is an ester of myristic acid, an essential fatty acid derived from palm kernel oil and isopropyl alcohol. These compounds disrupt the lipid coating that covers the head louse exoskeleton and protects it against water loss, resulting in dehydration.

Oxyphthirine is a formulation containing dimethicone, caprylic triglyceride, a component of coconut oil, and diisopropyl adipate. As with other silicone based products, it attaches to the respiratory orifices of lice and eggs to suffocate and dehydrate them.


Non-insecticidal method:

Wet combing is an alternative method for tackling the problem of head lice and resistance without the use of insecticides. The technique involves combing the hair while it is damp with a fine-tooth comb for about 30 minutes after shampooing and using conditioner.

If evidence of lice is found, the process should be repeated twice weekly for 2 weeks to remove lice emerging from eggs before they can spread and reproduce.


6.     One repellent spray is available. It contains IR3535 (ethyl butylacetylaminopropionate) which has been used safely and effectively for 30 years against insects and ticks carrying a range of human infectious diseases. It is also claimed effective against head lice, although there appears to be no published evidence.

To prevent re-infection following eradication of head lice during outbreaks, the manufacturer recommends daily use of the product.

7.     Head lice can affect anyone, including adults, but they occur most commonly in children aged between 4 and 11 years, in girls more than boys, in children with long hair, and at the start of the school year.

8.     Only those in whom current infection has been identified should be treated, as head lice preparations have no lasting prophylactic effect and unnecessary use of chemical insecticides encourages resistance.

However, when head lice infestation has been found everyone who has been in close contact with the infested person in the previous weeks should be examined for lice by wet combing and treated if necessary. 

9.     Most head lice treatments can be used for babies and children from the age of 6 months. The NHS advises that dimeticone 4 per cent lotion can be used on infants from the age of one month, but that infants under six months should be treated with dimeticone 4 per cent or malathion under medical supervision only.

Dimeticone 92 per cent and isopropyl myristate/cyclomethicone are not considered suitable for infants below the age of two years.

10.  A useful, comprehensive source of information on head lice is: UKMI (Wales). Head Lice. Questions & Answers for Healthcare Professionals. January 2014.  (

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