Head lice (Pediculus humanus capitis) are tiny parasitic insects that live on the human scalp and feed on blood. Visual identification is the necessary first step toward successfully treating an infestation. Understanding the color and appearance of the different life stages—from eggs to adults—is important because their look changes significantly throughout their life cycle.
The Primary Color and Variations
A mature, unfed head louse is typically grayish-white, tan, or pale beige, allowing it to blend into the hair and scalp. Adult lice are small, generally about the size of a sesame seed. The body is somewhat translucent when it has not recently consumed a blood meal, making them challenging to detect as they move quickly and actively avoid light.
The louse’s color changes noticeably after it has fed on blood from the scalp. Since head lice must feed several times a day, a recently fed louse appears reddish-brown or dark brown. This temporary change occurs because the ingested blood is visible through their bodies, making them much more visible against the pale scalp.
Appearance of Nits and Nymphs
The eggs of head lice are known as nits and represent the first stage of the life cycle. A viable, unhatched nit is tiny, oval-shaped, and firmly cemented to the hair shaft, usually appearing as a yellowish-white, tan, or brown speck. The female louse attaches the nits with a strong, waterproof, glue-like substance, typically within a quarter-inch of the scalp. This robust attachment helps distinguish them from simple debris like dandruff.
Once the nit hatches, a small, immature louse, called a nymph, emerges, leaving behind the empty shell. This remaining shell is translucent or whitish in color. Nymphs are smaller versions of the adult louse, often about the size of a pinhead, and are generally lighter in color than mature adults. Nymphs require regular blood meals and grow larger after each of their three molts before reaching full adult size.
Practical Tips for Visual Identification
Finding an infestation requires a thorough search, often starting with the areas where lice prefer to congregate. These insects favor the warmest spots on the scalp, typically the nape of the neck and the skin behind the ears. Using a bright light, such as a strong lamp or natural daylight, improves visibility, especially when looking for translucent lice or tiny nits. A magnifying glass can confirm the shape and color of any suspects found.
The most reliable way to differentiate nits from common look-alikes, such as dandruff, hairspray residue, or skin flakes, is by testing their adherence to the hair. Dandruff and other debris easily flake off the hair shaft with a gentle flick or brush. In contrast, a nit is securely glued to the hair shaft. Attempting to slide it off will show that it is stuck firmly in place. Finding an object that is hard to move and consistently oval-shaped indicates a louse egg.