Curriculum · ENT, Ophthalmology, and Dermatology
Head lice
What it is
Pediculosis capitis is a hair infestation caused by Pediculus humanus capitis, the head louse. It spreads by close physical contact or by sharing fomites such as clothes, and it commonly affects children 3-11 years old. It causes scalp pruritus, with or without lymphadenopathy. The picture in one line is an itchy scalp with nits on the hair shafts in a child.
It is a relatively common infestation in school-aged children and adolescents, but it is often unnecessarily feared and affected children are stigmatized. That line is the reason the rest of the entry reads the way it does: most of what is written about head lice is written to stop people from doing too much.
Nits, and what they do not prove
Nits are louse eggs and do not necessarily represent an active, infectious case of head lice. That is the single most useful line in the topic, because a nit seen on a hair shaft is what usually sets off the whole chain of exclusion and treatment.
Diagnosis is by physical exam: lice plus nits, inspecting for nits and lice. And because transmission rates are relatively low in the classroom setting, and treatments can be expensive and difficult, a child should not be treated unless there is a clear diagnosis. The material does not set out how a nit is told apart from scale on inspection; what it gives instead is the rule that finding nits alone is not enough to act on.