A nit is the egg of a head louse, a tiny parasitic insect that lives on the human scalp and feeds on blood. Identifying these eggs is the most common indicator of lice presence, as live lice are often difficult to spot due to their size and speed. Knowing the physical details and location of a nit is necessary for a successful inspection.
The Visual Characteristics of a Nit
A nit is significantly smaller than a grain of rice, often compared in size to a pinhead or a knot in a strand of thread, measuring approximately 0.8 millimeters in length. Due to this minute size, a strong light or magnification is often needed to see the object clearly. The shape of a nit is distinctly oval or teardrop-like, with a slight point at one end where it attaches to the hair shaft.
The color of the nit changes depending on its stage of development. A viable, newly laid egg containing an embryo typically appears darker, ranging from translucent to a yellowish-white, tan, or even dark brown shade. Once the louse nymph hatches, the remaining egg casing stays cemented to the hair, becoming clear, hollow, and often turning a whitish color. The shell has a hard texture and a slightly reflective sheen, unlike soft or flaky substances commonly found in hair.
How to Differentiate Nits from Hair Debris
The most important physical characteristic that distinguishes a nit from other hair particles is how it is secured to the hair shaft. Female lice secrete a powerful, specialized glue composed of chitin and protein that permanently cements the egg to the side of an individual hair strand. This adhesive bond is so strong that the nit cannot be simply brushed away or flicked off the hair with a finger, which is the primary test for identification.
Common look-alikes, such as dried hair spray droplets or product residue, will move easily when touched. Dandruff, which is composed of shed skin cells, is typically irregular in shape and loose on the scalp or scattered throughout the hair. A confirmed nit must be physically pulled or slid off the hair shaft with a fingernail or a specialized fine-toothed comb to be dislodged; if the object slides without resistance, it is not a nit.
Typical Location of Nits on the Hair Shaft
The placement of nits on the hair is dictated by the biological need for warmth. Lice require the consistent, high temperature of the scalp to successfully incubate their eggs. Consequently, female lice lay their eggs very close to the scalp, typically within a range of 1/4 to 1/2 inch from the skin.
As the hair grows, the nit remains fixed to the strand, meaning nits found further down the hair shaft are older and are likely already hatched or non-viable. When inspecting the head, attention should be focused on areas where the scalp’s temperature is most stable. These preferred locations are most often the hair near the nape of the neck and behind the ears.