GPAtlas🧭 When to suspect
Head lice (pediculosis capitis) are an infestation of the scalp by Pediculus humanus capitis, a wingless grey-brown insect about 2–3 mm long:
• Lives only on the human head, feeds on blood, and dies within a day or two away from the scalp.
• One of the commonest conditions of childhood, peaking in children aged roughly 4–11 years and slightly more frequent in girls.
• Lice cannot fly, jump, or burrow; they spread almost entirely by head-to-head contact, which is why cases cluster within families and classrooms.
Suspect head lice in a child with an itchy scalp, classically behind the ears and at the nape of the neck:
• The itch is an allergic response to louse saliva and may take several weeks to develop.
• So asymptomatic infestation is common, and itch is neither sensitive nor specific.
Treat only when a living, moving louse is found.
• Eggs alone – whether unhatched, or the empty white cases (nits) left after hatching – are not proof of active infestation.
• Itch by itself is not a reason to treat.
| What you find | What it means |
|---|---|
| Live, moving louse | Active infestation → treat |
| Unhatched eggs close to the scalp | Possible active infestation → confirm by finding a live louse before treating |
| Nits (empty white cases), often > 1 cm from the scalp | Old or resolved infestation → do not treat on this alone |
Source: DermNet · British Association of Dermatologists
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