How is pediculosis and pthiriasis (lice infestation) diagnosed?

Updated: Aug 16, 2019
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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A diagnosis of any type of pediculosis rests on the observation of eggs (nits), nymphs, or mature lice. Definitive diagnosis of active infestation requires detection of live lice. Nits are not diagnostic of an active infestation; however, if they are within 6 mm of the scalp, active infestation is probable. Viable nits may be found 8 or more inches from the scalp in warm climates. [6] Nymphs and mature lice, although unable to hop or jump, can move rapidly through dry hair. Wetting the hair and using a fine-tooth "bug-busting" comb is useful to dislodge eggs and to remove live lice/nymphs. The use of a magnifying glass and knowing where to look for lice (based on the biology of each species) assists in the diagnosis.

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