Head lice are gray or red-brown in color and can vary in size from 2 mm (1/8 inch) in size to just under 5 mm (1/4 inch) long. Their eggs, called nits, are attached directly to the hair at or near the hairline with a powerful glue-like substance and are white or clear in color. Sometimes it is difficult to tell the difference between nits and dry scalp. A quick test is to hold on to the hair shaft and flick it with your finger. If it moves, it is dry scalp. If it does not move, it is most likely a nit.
It is possible to tell how long the person has had lice by the location of the nits: the closer to the scalp, the fresher the nit.