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Pediculosis capitis

Adam O Goldstein, MD, MPH
Beth G Goldstein, MD
Section Editors
Robert P Dellavalle, MD, PhD, MSPH
Moise L Levy, MD
Ted Rosen, MD
Deputy Editor
Abena O Ofori, MD


Pediculosis capitis is a common condition caused by infestation of the hair and scalp by Pediculus humanus capitis (the head louse), one of three distinct varieties of lice specifically parasitic for humans (figure 1) [1]. The clinical manifestations, diagnosis, and treatment of pediculosis capitis will be reviewed here. Other forms of louse infestation, including pediculosis corporis and pediculosis pubis, are discussed separately. (See "Pediculosis corporis" and "Pediculosis pubis and pediculosis ciliaris".)


Pediculosis capitis occurs worldwide and in individuals of all socioeconomic backgrounds [2]. Children are affected most frequently.

Males appear to be less susceptible to lice infestations than females [3-5], and in the United States, black children are affected much less frequently than white children and others [6]. The reasons for these findings are uncertain. Studies investigating the impact of long hair length on the risk for infestation have yielded conflicting results [3,4,7]. The lower incidence in black children in the United States may be related to a low prevalence of lice that are capable of grasping the shape or width of certain types of hair [6].


The life span of the female louse is about one month, during which she lays 7 to 10 eggs per day, cementing them firmly to the base of a host hair. The eggs, commonly called "nits," are oval capsules that hatch in eight days, releasing nymphs that require another eight days to mature (picture 1A-B). After hatching, egg cases become white and more visible.

Adult head lice are gray-white, 2 to 3 mm in length (picture 2A-B), and equipped with mouth parts adapted to sucking blood and legs adapted to grasping hairs. Adults feed both on the scalp and adjacent areas of the face and neck. Adult lice can survive up to 55 hours without a host [8] but probably dehydrate and become nonviable long before their death [2].

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Literature review current through: Nov 2017. | This topic last updated: Aug 16, 2017.
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