Head Lice

🔍 When to Suspect

A child with an itchy scalp, particularly behind the ears and at the nape of the neck; diagnosis is only confirmed by finding a live louse

From the full topic in The Ocean Library: Head Lice

🧭 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 that lives only on the human head, feeds on blood, and dies within a day or two away from the scalp. It is 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.

The single most important principle is diagnostic: 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, and 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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