Lice can be very slow to show symptoms, which is why we recommend that families be screened if they suspect they have been exposed to lice. While head lice bites on the scalp can cause the itchy welts associated with head lice, it can often take several weeks for this symptom to appear, by which time a full blown infestation may be underway. Scalp itchiness may also have other causes.
Some will report tickling or moving sensations in the hair and on the scalp, but this is also not a perfect indicator of the presence or absence of lice. A professional screening is needed in order to be sure.