Cathy Cooke shares the latest advice for pharmacists to share with patients on this common lice infestation


Key learning points

  • The only reliable confirmation of infestation is detection of one or more live lice
  • Treat all affected members of the household at the same time
  • Choose a treatment option based on the advantages and disadvantages and the individual needs of the people to be treated
  • Use detection combing to check if treatment has been successful


Requests for advice and treatment for head lice infestation are a regular occurrence in community pharmacy. Parents finding evidence of lice on their child for the first time are often shocked and embarrassed.


Therefore, the provision of accurate, practical information can reassure and help with effective treatment of the individuals, as well as contributing to the control of infestation in the wider community. The current prevalence of infestation in the UK isn’t accurately known, but historic data1 suggested between four and 22% of school age children could be affected at any one time.


Life cycle


A wingless insect 1 to 3 mm long, the ectoparasite Pediculus humanus capitis spends its entire life on the human head, feeding several times a day exclusively on blood. The eggs are oval, translucent and firmly attached with a glue-like substance to hairs, close to the scalp.


When the eggs hatch after about seven to 10 days, the empty egg cases (nits) become yellowish white and are more noticeable. The immature lice (nymphs) take a further seven to 10 days to mature into adults, when they start to reproduce, with females laying up to eight eggs a day. Adult lice have a lifespan of about 30 days. 1-3




Head lice can neither fly nor jump. The mode of transmission is thought to be almost entirely by head to head contact. They can live for a short period off the human head; estimates vary within the range 12 to 48 hours, so if they become dislodged transfer is possible via direct contact with inanimate objects such as shared headgear. 1,2


Risk factors


Although head lice infestation can affect people of any age, it is most common in children of primary school age (four to 11 years) with a peak at seven to eight years. 1-3


Evidence on risk factors comes from a Belgian study4 investigating the independent association between characteristics of the child, family socio-economic status and head lice. The authors identified hair length, hair colour, socio-economic status and the number of children in the family as the only statistically significant factors for head lice in children.


Hair length and colour may relate to the difficulty of treating long hair and of noticing signs of infestation. Larger families may face practical difficulties in checking and treating all children. The requirement to purchase treatment products can disadvantage families of low socio-economic status.


Clustering of children, such as in large families or in class at school, was judged to have more influence on prevalence compared with characteristics such as hair length or socio-economic status.




Head lice infestation commonly presents when nits or adult lice are spotted, or with itching. The presence of nits alone does not confirm a current infestation, as the empty egg cases remain firmly attached to the hair shafts and persist following eradication of lice.


Itching usually develops between two to six weeks after first exposure to feeding lice, typically from an immune-mediated hypersensitivity reaction. In the event of a future infestation, itching can develop in one to two days from exposure.


Pharmacists should advise patients to use a fine-toothed plastic detection comb, with teeth 0.2 to 0.3mm apart, to confirm the presence of lice. Dry combing or wet combing can be used for detection; wet combing with conditioner has the advantage that the conditioner immobilises the lice so they are easy to see on the comb.




When infestation has been confirmed by the presence of a live louse, treatment can be started. All affected members of the household should be treated at the same time. There is limited evidence on the effectiveness of different head lice treatments and no clear superiority of one method, so factors such as contraindications, cautions, individual choice and previous product or method used should be considered.


Compliance with treatment instructions is important for optimising its effectiveness, so ensuring that the customer understands the regime and the need to complete all stages, including checking the success of the treatment, is a key intervention.


There are three treatment options available:

  • Physical insecticide – a silicon or fatty acid ester-based product that coats the lice and suffocates them. These include dimeticone 4% gel, lotion and spray; dimeticone 92% spray; dimeticone >95% lotion; isopropyl myristate and cyclomethicone solution; and isopropyl myristrate and isopropyl alcohol aerosol. Two applications are generally advised at least seven days apart to catch lice hatching from eggs before they mature and start laying.
  • Chemical insecticide – a pharmacologically active product that paralyses the lice. The only product currently recommended for use in the UK is malathion 0.5% aqueous liquid (Derbac-M®), but there is evidence5 of resistance to malathion, particularly in the UK. Two applications are generally advised at least seven days apart to catch lice hatching from eggs before they mature and start laying.
  • Wet combing – the use of a fine-toothed comb on wet hair coated in conditioner to systematically remove lice. The recommendation is that the procedure is carried out four times over a two-week period, on days one, five, nine and 13. Of the range of fine-tooth combs marketed, ensure a product of the correct specification is supplied for removing lice as some are for the removal of empty egg cases (nits) and the tooth spacing may be wider than that required for removing lice.


There are advantages and disadvantages for each option but wet combing or dimeticone 4% lotion is recommended as first-line choice for:

  • Pregnant and breastfeeding women;
  • Children aged six months to two years;
  • People with asthma or eczema.


After treatment


Detection combing should be carried out to check if treatment was successful. With insecticides, recommendations vary on the frequency of detection combing. One regimen is to check two to three days after treatment and again seven days later; another suggests checking at days five, nine and 12 to 13 after the first application. With wet combing, a fifth session is carried out on day 17.


If there is treatment failure, check that the relevant procedure was followed correctly. The same treatment can be repeated but used accurately, or a different treatment option can be tried.




Prevention measures are generally of limited success. Keeping long hair tied back and regular combing with a fine-toothed comb may help. Don’t use insecticides for prevention.


Further information and patient leaflets









  1. Clinical Knowledge Summaries: Headlice. (accessed 5 February 2018)
  2. Bragg BN, Simon LV. Pediculosis Humanis (Lice, Capitis, Pubis) [Updated 2017 Nov 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2017 Jun-. Available from: (accessed 5 February 2018)
  3. Patient Professional Reference: Head Lice. (accessed 5 February 2018)
  4. Willems S, Lapeere H, Haedens N, et al. The importance of socio-economic status and individual characteristics on the prevalence of head lice in schoolchildren. European Journal of Dermatology. 2005;15(5), 387-392. Abstract. (accessed 5 February 2018)
  5. Durand R, Bouvresse S, Berdjane Z, et al. Insecticide resistance in head lice: clinical, parasitological and genetic aspects. Clinical Microbiology and Infection. 2012;18(4), 338-344. Clinical Microbiology and Infection (accessed 5 February 2018)



Cathy Cooke is a clinical pharmacist with experience of community pharmacy, primary care, urgent care, social care, secure environments.