What are the characteristics of lice nits in pediculosis and pthiriasis (lice infestation)?

Updated: Aug 16, 2019
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

The average nit (ie, ovum) of the 3 types of lice is 0.8 mm long. The nit (see the images below) attaches to the base of the hair shaft (in the case of head or pubic lice) or to fibers of clothing (in the case of body lice) with a strong, highly insoluble cement; thus, nits are difficult to remove. The nit is topped with a tough but porous cap known as the operculum. This porous operculum allows for gas exchange while the nymph develops in the casing.

Nit on a hair. Note the thin, translucent cement s Nit on a hair. Note the thin, translucent cement surrounding the hair shaft. Photo courtesy of David Shum, MD Western University, London Ontario.
Two empty nits from Pediculus humanus capitis. Not Two empty nits from Pediculus humanus capitis. Note the open shells still attached to the hairs and the porous operculi through which the lice have hatched. Photo courtesy of David G. Schaus.

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