Head lice (Pediculus humanus capitis) are small parasitic insects that live on the human scalp and feed on blood. They are common, particularly among school-aged children, and do not indicate poor hygiene. Although visible to the naked eye, their small size and ability to camouflage make them challenging to spot without a careful search. Understanding the visual characteristics of the different life stages is the most practical step toward identifying an infestation. This guide describes what to look for when inspecting the hair and scalp.
The Appearance of Nits
The first indication of an infestation is often the presence of nits, which are the eggs laid by the female louse. These minute, oval-shaped capsules typically measure about 0.8 millimeters in length, roughly the size of a poppy seed. They are firmly cemented to the side of the hair shaft with a powerful, waterproof, glue-like substance.
A viable nit is usually yellowish or pearl-white and may appear translucent when held up to a light source. Because they require the warmth of the scalp to incubate, nits are almost always found within one-quarter inch of the scalp. They are commonly located in warmer areas of the head, specifically behind the ears and at the nape of the neck.
If the egg has hatched, the resulting empty shell remains glued to the hair but becomes more translucent or dull yellow. These empty casings are found further down the hair strand as the hair grows out, indicating a past infestation. Nits close to the scalp suggest a current, active infestation. The firm, fixed attachment to the hair shaft is the most distinguishing feature.
Identifying Adult Lice
The mature head louse is a small, six-legged insect, comparable in size to a sesame seed, measuring between two and three millimeters long. The adult louse is wingless and possesses specialized claws designed to grip the hair shaft securely. Lice typically appear tan or grayish-white, but they can temporarily take on a reddish-brown hue immediately after feeding on blood.
Adult lice are difficult to spot because they are highly mobile and actively avoid bright light. They move with a rapid crawl, staying close to the scalp; they are not capable of jumping or flying. Nymphs, or immature lice, look like miniature versions of the adults but are smaller and more translucent.
The presence of live, crawling lice confirms an active infestation, though they are often outnumbered by the more easily visible nits. Intense itching or the feeling of movement on the scalp may be the first sensory clue. A thorough search using a fine-toothed nit comb is often the most effective way to detect the live adult bugs.
Distinguishing Lice from Common Lookalikes
Many common forms of hair debris are mistaken for nits, leading to unnecessary panic and treatment. Dandruff is a common lookalike, appearing as white or yellowish flakes that are easily brushed off the hair and scalp. In contrast, nits are firmly glued to the hair shaft and require deliberate action, such as pulling them off with fingernails or a specialized comb, for removal.
Hair casts, which are small, white, sheath-like structures that encircle the hair shaft, can also cause confusion. Unlike the oval, teardrop-shaped nit cemented to one side of the hair, hair casts are tubular and slide easily up and down the strand. This simple movement test immediately distinguishes them from the fixed nit.
Other debris, such as residual hair product, lint, or dirt, tends to be irregular in shape and inconsistent in color. True nits, whether live or empty, maintain a uniform, oval shape and a consistent appearance. If an object is irregular, crumbles easily, or is not firmly attached to the hair shaft, it is not a nit.
Confirming the viability of a nit is also a key distinction, as empty egg casings do not require treatment. Nits found more than a quarter-inch from the scalp are considered non-viable, simply being the shell of a hatched or dead louse. An active infestation is confirmed only by the presence of a live adult louse or a viable nit found close to the scalp.