A nit is the egg of a head louse, the parasitic insect responsible for head lice infestations. These oval-shaped capsules are firmly cemented to a hair shaft by a female louse. Nits are small and often translucent or pale, making them difficult to spot. Their presence confirms an active infestation.
Identifying Nits: Size, Shape, and Location
Nits typically measure 0.8 to 1.0 millimeter in length, comparable to a knot in thread or a speck of sand. They possess a distinct oval or teardrop shape. Viable eggs appear yellowish-white or tan, while empty or dead shells look paler white or clear.
The female louse secretes a powerful, water-insoluble substance to secure the nit to the hair shaft. This cement holds the egg at a slight angle on one side of the hair strand. Nits are almost always found within 6 millimeters (about one-quarter inch) of the scalp. This placement is intentional because the eggs require the consistent warmth from the scalp to successfully incubate and hatch. Nits found further down the hair shaft have likely already hatched or are no longer viable, as the hair has grown out since they were laid.
How Nits Differ from Dandruff and Other Residue
Nits are frequently mistaken for common hair debris like dandruff, dried hair spray, or hair casts. The most reliable way to differentiate a nit from other particles is by testing its adhesion to the hair. Dandruff, which consists of irregular flakes of dead skin, easily slides off the hair shaft or can be flicked away.
In contrast, a nit is securely cemented and resists movement, requiring a specialized fine-toothed comb or a fingernail to pull it off. Dandruff can be found anywhere on the scalp and hair, while nits maintain a uniform, oval shape and are consistently attached to the hair fiber. Hair casts, which are white, tube-like pieces of debris, also slide easily along the hair, unlike the firmly attached nit.
The Nit’s Role in the Lice Life Cycle
The nit represents the first phase of the head louse’s three-stage life cycle, progressing to nymph and then adult louse. Its primary function is to protect the developing louse until it is ready to emerge. Inside the casing, the embryo develops over seven to ten days before hatching.
Once the nit hatches, a small, immature louse called a nymph emerges, immediately beginning to feed on the host’s blood. The remaining empty shell, still firmly attached, is referred to as a nit casing. Since many common treatments target only live lice, remaining viable nits can hatch and lead to a recurring infestation. Successful eradication requires the removal or destruction of all nits to prevent the cycle from continuing.