Criteria
Live lice on the head
Finding live lice on the head is the definitive standard of diagnosis. Sometimes this can be accomplished by casual observation, separating sections of hair at the nape of the neck or behind the ears with fingers or sticks. Hair can be combed with a fine-toothed comb, with inspection of the comb for lice between strokes. The highest yield is from combing hair moistened with water or conditioner (wet combing), as this slows down the movement of the lice.[9][31][32]
Eggs visible on hair shaft within 1 cm of scalp
When combing is not convenient, some will accept the presence of live eggs on hair shafts within 1 cm of the scalp as a diagnostic criterion for head lice infestation. Live eggs develop an eyespot that can be seen microscopically within several days of being laid. Not all children with eggs alone will go on to develop an actual infestation. Empty egg cases (nits), especially on hair shafts >1 cm from the scalp, should not be considered criteria for diagnosing head lice infestation.[29]
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