Pediculosis Capitis
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Direct answer
Pediculosis capitis is infestation of the scalp hair by the human head louse, Pediculus humanus capitis, a blood-feeding insect that spreads mainly through direct head-to-head contact. Intense scalp itching and nits glued to the hair shafts close to the scalp are the classic clues. Live lice or nymphs confirm the diagnosis, and permethrin 1 per cent cream rinse, repeated after seven to ten days, is the standard first-line treatment.
What you must remember
- Organism: Pediculus humanus capitis, a wingless obligate ectoparasite that lives on the human scalp and feeds on blood several times a day.
- Life cycle: eggs, called nits, hatch in about seven to ten days, nymphs mature in roughly nine to twelve days, and adults live for around a month on the host.
- Transmission: direct head-to-head contact is the main route, since lice survive only a day or two away from the scalp.
- Clinical features: pruritus from hypersensitivity to louse saliva, excoriations, posterior cervical lymphadenopathy and occasional secondary impetiginisation.
- Confirmation: live lice or nymphs are the only confirmatory finding and are usually seen behind the ears and at the nape, whereas nits alone do not prove active infestation.
- Nit position: eggs attached within about one centimetre of the scalp suggest current infestation, while those lying further out are usually empty or already hatched.
- First-line treatment: permethrin 1 per cent cream rinse on towel-dried hair for about ten minutes, repeated at seven to ten days, with wet combing as an adjunct.
- Avoid: lindane, because of its neurotoxicity in children, which is why it is not used as routine therapy.
A stepwise approach from diagnosis to clearance
A 7-year-old girl has itching behind the ears for a week, and her mother finds small white specks clinging to the hair near the scalp. The approach runs in a fixed order.
- Confirm live lice. Examine wet hair under a bright light with a fine-toothed nit comb, since finding live lice or nymphs separates active infestation from old nits.
- Exclude look-alikes. Dandruff flakes slide off the hair, and scalp scaling with patchy hair loss should prompt a check for tinea capitis rather than lice treatment alone.
- Apply first-line permethrin. Apply 1 per cent permethrin cream rinse to towel-dried hair, leave it on for about ten minutes and rinse it off.
- Repeat at seven to ten days. A second application kills nymphs that hatch from eggs surviving the first treatment, so a single application is seldom enough.
- Add wet combing. Comb wet hair with a fine-toothed nit comb every few days over about two weeks to remove lice and nits mechanically, which is a useful non-chemical adjunct.
- Manage the environment and contacts. Wash washable bedding, clothing and towels in hot water, seal non-washable items in a plastic bag for about two weeks, and treat close contacts only if they have live lice.
Where the exam tries to catch you
Most errors come from mixing up diagnosis, drug choice and follow-up.
- Trap: choosing lindane as the first-line drug because it is a standard scabicide Correct: permethrin 1 per cent is first-line, and lindane is avoided in children because of neurotoxicity.
- Trap: calling scalp scaling with nits the same as dandruff Correct: dandruff flakes move freely, but nits are fixed to the hair shaft and do not slide off.
- Trap: stopping treatment after one application Correct: surviving eggs hatch after seven to ten days, so the repeat application is part of standard treatment.
- Trap: excluding a child from school for nits alone Correct: current guidance discourages no-nit policies, and the child can usually return after the first treatment.
Frequently asked questions
Which drug is first-line for pediculosis capitis in children?
Permethrin 1 per cent cream rinse is the first-line drug for pediculosis capitis in children. It is applied to towel-dried hair, left on for about ten minutes, rinsed off and repeated after seven to ten days.
Why is a second application needed in pediculosis capitis?
A second application is needed in pediculosis capitis because permethrin does not reliably kill the eggs. Eggs that survive the first treatment hatch after seven to ten days, and the repeat dose kills the newly emerged nymphs before they mature and lay eggs.
How does pediculosis capitis differ from dandruff on the scalp?
Dandruff flakes are loose and slide off the hair when it is brushed or gently pulled. Nits in pediculosis capitis are oval eggs glued firmly to the hair shaft near the scalp, so they do not slide off easily.
Is lindane recommended for head lice in children?
Lindane is not recommended for head lice in children because of its neurotoxicity, including the risk of seizures. Permethrin 1 per cent or dimeticone is preferred instead.
Should children with head lice be excluded from school?
Children with head lice are generally not excluded from school under current guidance, which discourages no-nit policies. The child can return after the first treatment.