Head lice eggs, known as nits, are tiny and oval-shaped. They are firmly glued to individual hair shafts, making it challenging to determine if an active infestation is still present. Correctly identifying whether a nit is alive or dead is important for deciding on treatment, and the color and location provide the most reliable clues about their viability.
Identifying Live Nits
Viable nits, which contain a developing louse embryo, are almost always found very close to the scalp. The female louse strategically attaches them within a quarter-inch (about 0.6 cm) of the skin to ensure they receive the necessary warmth for incubation. This proximity to the body temperature is required for the egg to hatch successfully, which typically occurs within six to nine days.
A live nit is typically translucent, yellowish, or pearl-colored, and may appear shiny. As the embryo inside matures and nears hatching, the nit can darken, sometimes presenting as a tan, amber, or pale brown color. The developing louse creates a pigment that gives the egg its darker hue, signaling that it is actively growing.
The attachment itself is another strong indicator of viability. The louse secretes a cement that permanently affixes the nit to the hair shaft, making it resistant to gentle pulling or washing. This strong bond distinguishes nits from easily flicked-off debris like dandruff, and any nit difficult to dislodge near the scalp should be treated as a live, unhatched egg.
What the Color Brown Indicates
The color brown in a nit can be misleading because it may indicate two different states: an egg close to hatching or one that has died. Darker coloring, ranging from medium to dark brown, often suggests the embryo is fully developed and ripe for hatching. This pigmentation results from the growing internal structures of the louse becoming visible through the shell, meaning a dark brown nit cemented near the scalp is almost certainly viable.
Conversely, the color brown or black can also indicate that the nit is non-viable, meaning the embryo has died before hatching. In this case, the dead louse embryo inside darkens and becomes opaque, giving the nit a dull, brown, or sometimes black appearance. These dead nits retain their firm attachment because the glue does not dissolve upon the death of the embryo. They may look shriveled or sunken compared to the plump appearance of a live egg.
Location on the hair shaft provides the most reliable distinction when a nit is brown. Since hair grows about a half-inch (1.27 cm) per month, nits found more than one centimeter away from the scalp are unlikely to be viable, regardless of color, as they lack the necessary warmth. Therefore, a brown nit far down the hair shaft is almost certainly a remnant of a past infestation, either dead or an old, darkened empty casing.
Why Removal Is Still Essential
Even when a nit is confirmed to be dead, hatched, or located far from the scalp, its physical removal remains essential. The strong, water-insoluble cement that secured the nit to the hair shaft does not degrade after the louse has emerged or the embryo has died. The casing remains anchored to the hair until it is physically removed or cut out.
Removing all nits, both viable and non-viable, is important for hygiene and to ensure a correct diagnosis moving forward. The presence of non-viable nits can easily be mistaken for an ongoing, active infestation, leading to unnecessary worry and repeated, ineffective treatments. Furthermore, many schools or organizations have policies that prohibit attendance if any nits are visible, regardless of their viability.
The primary method for physical removal involves specialized fine-toothed combing. This process is most effective when the hair is wet and coated with a conditioner, which temporarily immobilizes any live lice and makes the nits easier to slide off the hair shaft. Thorough combing, section by section, is the only guaranteed way to eliminate both the live eggs and the casings.