Confirming a head louse infestation (pediculosis capitis) requires visually identifying the tiny insects or their eggs. Many people misunderstand the actual appearance of the head louse (Pediculus humanus capitis), often confusing them with harmless debris found in the hair. Knowing precisely what a louse looks like across its life stages is the first step toward accurate identification and treatment.
The True Color of Head Lice
The notion that head lice are consistently brown is a common misconception, as the true color of the living insect varies depending on its feeding schedule. Before an adult louse feeds, its body is primarily translucent, giving it a grayish-white or tan appearance. This coloration allows the small insect, which measures approximately 2.5 to 3 millimeters long, to blend into the hair and scalp. Head lice are wingless and have a flattened body with six legs, each equipped with a claw specialized for tightly grasping a hair shaft.
The striking color change occurs immediately after a blood meal. Head lice are obligate parasites, meaning they must feed exclusively on human blood several times a day to survive. When a louse ingests blood, the blood is visible through its transparent outer shell, causing the louse to take on a reddish-brown or dark brown hue. This engorged appearance lasts for a few hours until the blood is digested. Since an infestation involves lice at various feeding stages, a person may observe a mix of translucent, tan, and reddish-brown insects.
The mobile louse is fast-crawling and often avoids light, making spotting them in the hair difficult. The smaller, newly hatched nymphs look like miniature versions of the adults and exhibit the same color range based on recent feeding.
Identifying Nits and Empty Casings
While finding a mobile louse confirms an active infestation, the stationary eggs, or nits, are often the first sign of a problem. A live, unhatched nit is an oval-shaped sac, measuring about 0.8 millimeters in length, and is firmly cemented to the hair shaft. These developing eggs are typically yellowish, beige, or tan, sometimes appearing darker brown if close to hatching. The female louse secretes a waterproof, glue-like substance to attach the nit to the hair, usually within a quarter-inch of the warm scalp, as nits require the host’s body heat to incubate.
Once the louse hatches, the remaining egg shell is termed a nit casing. These empty casings are easier to see as they appear lighter, often a white or translucent color, especially against darker hair. Because the empty casing remains glued to the hair, it moves farther down the shaft as the hair grows. Finding a nit more than a half-inch from the scalp suggests the infestation is older or potentially resolved.
Common Look-Alikes
Visual confirmation of nits is complicated by common hair and scalp debris that resemble them. Dandruff, consisting of flakes of dead skin, is the most frequent item mistaken for nits. Unlike nits, dandruff flakes are irregularly shaped and can be easily brushed or flicked away from the hair shaft. Nits, due to their specialized cement, resist being removed with a simple flick of the finger.
Another common look-alike is a hair cast, sometimes called a keratin cast, which is a small, cylindrical piece of debris that encircles the hair shaft. These casts are white or pale in color but can be distinguished from nits because they slide effortlessly along the length of the hair. Residue from hair products, such as hairspray droplets or conditioning agents, can also solidify into tiny white specks. These product deposits, like dandruff and hair casts, will move or fall off the hair easily.