Head Lice (Pediculosis Capitis)

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Head lice\: common parasite infestation known as p e d i c u l o s i s c a p i t i s ; a
A
Transmission\: direct head-to-head contact; lice cannot
Life cycle\: adults live up to 30 days, females lay up to 10 eggs daily, eggs hatch in 7-10 days, cycle repeats every three
weeks if untreated.
Risk factors\: age 4-11 years, female sex, sharing personal items, larger families, overcrowded living conditions.
Symptoms\: scalp itching, feeling of movement in hair, scratching causing crusting and scaling.
Examination\: visible nymphs or adult lice, eggs on hair shafts, red papules at nape of neck and behind ears, possible
cervical lymphadenopathy.
Di
Diagnosis\: clinical, con
Management\: treat with over-the-counter topical insecticides (e.g., dimeticone) and wet combing; inform close contacts
and treat simultaneously if infected.
Topical therapy\: physical insecticides (e.g., dimeticone) recommended; apply at least twice, 7-10 days apart.
Wet combing\: systematic combing of wet hair with a
for pregnant/lactating women.
Complications\: secondary bacterial infection (impetigo), dermatitis, anxiety/distress, lymphadenopathy.
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A comprehensive topic overview

Introduction

Head lice are a common parasite infestation known as p e d i c u l o s i s c a p i t i s . The head louse (P e d i c u l u s h u m a n i s c a p i t i s )
infests the hairs on the scalp and feeds on human blood.
Anyone can catch head lice, but typically, it a

Aetiology

Head lice are most commonly spread by direct head-to-head contact, allowing the lice to crawl from one host to another.
Head lice cannot
A louse can only survive 1-2 days away from a human host.
Head lice life cycleAdult lice are 2-3mm in length, with six legs to cling to hair shafts. They inject the scalp with saliva and feed on human
blood, which causes itching and irritation. The females lay up to 10 eggs daily, and adult lice live up to 30 days.Louse eggs (ova or nits) are oval and brown but become yellowish-white once hatched. They can be easier to spot than
adults. Eggs are laid close to the scalp and attached to hair shafts, taking just over a week to hatch.
Nymphs (baby lice) take 7-10 days to mature. After maturing, they mate, and the females lay eggs, restarting the cycle.
Untreated, the cycle repeats every three weeks.
Figure 1. Head louse and egg (nit)
Figure 2. Female human head louseFigure 3. Human head louse egg (nit)

Risk factors

Risk factors for head lice include\:
Age 4-11 years
Female sex
Sharing beds, clothing, and hairbrushes
A greater number of children in the family
Overcrowded living conditions

Clinical features

History
Typical symptoms of head lice include\:
Scalp pruritus (itching)
The feeling of things moving in the hair
Scratching, causing crusting and scale
Clinical examination
On visual inspection of the scalp, there may be visible live nymphs or adult lice and eggs visible on the hair shaft within
1cm of the scalp (Figure 4).
Figure 4. Head lice eggs (nits) in the hair.
There may be small red papules under the hairline at the nape of the neck and behind the ears. These are louse bites.
Severe cases can also cause cervical lymphadenopathy.Di
Head lice can appear similar to the following dermatological conditions\:
Seborrheic dermatitis
Tinea capitis
Folliculitis

Investigations

Head lice are a clinical diagnosis on discovering a live nymph or adult louse. This can be done by combing the hair with a

Management

Managing head lice involves treatment to eliminate the lice and their eggs and preventative measures to avoid re-
infestation.
Most cases of headlice do not need medical input and can be treated with over-the-counter topical insecticides in
combination with a wet combing regimen.
Headlice should be treated as soon as they are spotted. Close contacts (including daycare/school) should be informed.
Other household members should be checked for headlice and, if infected, treated simultaneously to prevent re-
infestation.
Topical therapy
A physical insecticide is recommended, such as dimeticone. This kills the louse by coating it with a physical barrier,
causing su
Other treatments include insecticides like malathion, pyrethrin, permethrin or ivermectin. Although these are still
recommended treatments in the UK, there is widespread resistance to these insecticides, and they are highly
There should be at least two applications of insecticide. The second application should be 7-10 days after the
may survive, allowing new nymphs to hatch.
When other treatments have failed, consider ivermectin either orally or topically.
Wet combing
Wet combing is the systematic combing of wet hair with a
remove head lice. This can be used as an adjunct with topical therapy or
It is recommended to repeat wet combing in four sessions spaced over two weeks to catch any newly hatched head lice.
This should be repeated until no lice are found on consecutive occasions.
Wet combing or dimeticone should be used in pregnant or lactating women.

Complications

Head lice is not usually associated with severe complications. However, along with discomfort, it can cause\:
Secondary bacterial infection (impetigo)
Dermatitis\: red scaly, itchy plaques
Anxiety and distress
LymphadenopathyReferences
BMJ Best Practice. P e d i c u l o s i s c a p i t i s . Last updated Dec 2022. Available from\: [LINK]
Public Health England. H e a d l i c e ( p e d i c u l o s i s ) . Last updated Jan 2018. Available from\: [LINK]
Dermnet. H e a d l i c e . Last updated 2017. Available from\: [LINK]
NHS.uk. H e a d l i c e a n d n i t s . Last updated March 2021. Available from\: [LINK]
Image references
Figure 1. Cleveland Clinic. H e a d l i c e . License\: [CC BY-SA]
Figure 2. Gilles San Martin. F e m a l e h u m a n h e a d l o u s e . License\: [CC BY-SA]
Figure 3. Gilles San Martin. H u m a n h e a d l o u s e e g g . License\: [CC BY-SA]
Figure 4. KostaMumcuoglu. L o u s e n i t s . License\: [CC BY-SA]

Reviewer

Dr Katie Birks
General Practitioner

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