When they penetrate skin to get at someone's blood, lice inject saliva that causes irritation and itching. Lice also produce feces that looks like black dust. So, another sign is a little bit of dark, dust-like stuff on children's scalp, pillow or shirt collars. One reason lice are hard to identify is that they're tiny. Adult lice range in color from dirty white to grayish black.
Nits start out yellowish white and gradually become coffee-colored.
All like to stay close to the scalp in a human's hair, where they can be difficult to see. They usually won't roam into eyebrows or eyelashes unless driven by a large lice population. Added to that is the fact that most lice infestations include only a few dozen lice-although cases of much heavier infestations are on the books. You don't want to put your child through insecticidal treatments if he's just got dandruff. In that case, children often scratch until the abrasions get infected.