Because of their tiny size, head lice and nits often are detected with the aid of a hand lens or magnifying glasses. (Magnifying glasses are most helpful because both hands are free to inspect the hair.) High-intensity lighting, even natural sunlight, is very helpful for detecting nits. However, adults and nymphs move very quickly away from a light source and its associated warmth.
Head lice may look like grayish specks moving rapidly on the scalp and hair. Diagnosis based on adult and immature stages is difficult; they are easily overlooked. A head-lice infestation is most often diagnosed by observing the stationary nits glued to hair shafts very near the scalp. Nits may look like dandruff, but they cannot be shaken off.