What Do Lice Look Like? Adults, Nymphs, and Nits

Head lice are tiny, wingless insects roughly the size of a sesame seed as adults, tan to grayish-white in color, with six legs and a flattened oval body. Their eggs, called nits, are even smaller and appear as teardrop-shaped specks glued to individual hair strands near the scalp. Between those two stages sit nymphs, which look like miniature versions of adults but can be nearly invisible to the naked eye. Knowing what each stage actually looks like matters more than it might seem, because the most common reason infestations persist is that people miss what they’re looking for or confuse lice with something harmless.

What Adult Head Lice Look Like

An adult head louse (Pediculus humanus capitis) measures about 2 to 3 millimeters long, roughly the length of a sesame seed. Its body is elongated and flat, widest at the abdomen and narrower at the head. The color varies depending on when it last fed: an unfed louse tends to look pale tan or almost translucent, while one that has recently taken a blood meal appears darker, sometimes brownish-red, because you can see the blood through its semi-transparent exoskeleton. After a few hours the color fades back toward grayish-brown.

The head has two short antennae and a pair of simple eyes, though the eyes are small enough that you won’t notice them without magnification. The most distinctive anatomical feature is the six legs, each tipped with a strong curved claw. These claws act like hooks designed to grip a cylindrical hair shaft, and they are remarkably effective at it. Under magnification, the claw-and-thumb structure on each leg looks like a tiny set of pliers clamped around the hair. Adult lice cannot jump or fly. They move only by crawling, and they do so quickly, covering several centimeters per minute on hair, which is one reason they’re difficult to spot during a casual visual check.

Female lice are slightly larger than males and have a more rounded posterior end. Males have a somewhat more tapered abdomen. In practice, this sex difference is almost impossible to see without a magnifying lens, and it doesn’t change how you identify or treat them. The key visual cue for any adult louse is the combination of size (no bigger than a small matchstick head), six visible legs, and a flat body pressed close to the scalp or hair shaft.

The Three Nymphal Stages

After hatching, a louse passes through three nymphal stages, called instars, before reaching adulthood. The entire journey from hatchling to egg-laying adult takes about nine to twelve days. At each stage the nymph molts, shedding its old exoskeleton and emerging slightly larger and darker.

A first-instar nymph is tiny, roughly the size of a pinhead, and nearly colorless. It’s translucent enough that it can be almost invisible against a light-colored scalp. As it feeds, it darkens slightly, much the way adults do, but its small size still makes it extremely hard to see. Second-instar nymphs are a bit larger and begin to take on a more recognizable louse shape, with more distinct segmentation between head, thorax, and abdomen. By the third instar, the nymph looks very much like a small adult, with clear leg structure and a color that ranges from light tan to grayish brown. Even at this stage, though, it’s still smaller than a mature adult louse and easy to miss in thick or dark hair.

What trips people up is that a first- or second-instar nymph can be mistaken for a fleck of skin or a tiny bit of debris. If you see something on the scalp that is smaller than a grain of sand, translucent, and seems to be moving on its own, you’re likely looking at a young nymph. The movement is the giveaway: dandruff and dry skin don’t crawl.

What Nits Look Like on the Hair Shaft

Nits are the most commonly spotted sign of a lice infestation, mostly because they stay put. A female louse lays her eggs directly on individual hair strands, usually within about a centimeter of the scalp where the warmth is right for incubation. Each nit is oval-shaped, about 0.8 millimeters long, and attached to one side of the hair shaft by a cement-like sheath that the female secretes during egg-laying. The sheath wraps partly around the hair, making the nit extremely difficult to slide off with your fingers or a regular comb. Biochemical analysis has shown that this sheath is composed of proteins with a structure similar in composition to human hair itself, which is part of why it’s so tenacious and why products designed to dissolve it can also damage hair.¹

A viable nit, one with a developing embryo inside, appears yellowish to tan and slightly plump. It sits at an angle on the hair, almost like a tiny teardrop tilted to one side. When you look at it against a dark background or under good lighting, it has a faint sheen. After the nymph hatches, the empty casing stays glued in place but changes in appearance: it becomes white or nearly clear and looks flatter, more like a hollow tube than a rounded oval. These empty casings can remain on the hair for months, gradually moving farther from the scalp as the hair grows out.

The distance of a nit from the scalp surface can tell you something about how old the infestation is. Nits found very close to the root, within a couple of millimeters, are likely recent, while nits several centimeters away from the scalp have been there for weeks or months. In one study examining prehistoric lice specimens, viable nits were found as close as 0.2 centimeters from the scalp, consistent with eggs laid just days before, while empty casings were found as far as 9.5 centimeters out, pointing to an infestation that had been ongoing for many months.²

Things That Look Like Nits but Aren’t

One of the most common sources of unnecessary panic is mistaking other small particles on hair for nits. Several things can mimic nits visually, and even school nurses and pediatricians sometimes get it wrong on quick visual inspection.

Dandruff flakes: These are irregularly shaped, white, and flat. Unlike nits, dandruff flakes slide easily along the hair shaft or fall off when you touch them. Nits don’t budge without effort.
Hair casts: These are thin, white, cylindrical sheaths that encircle the hair shaft and can slide freely up and down. They’re made of cells from the inner root sheath or from skin conditions, and they sometimes cluster near the scalp in a way that mimics nits. The sliding test is the simplest way to tell them apart: hair casts move, nits don’t.
Hairspray or product residue: Dried product can leave small white or shiny clumps at the base of hair strands. These tend to feel gritty or sticky and are irregular in shape, whereas nits are smooth and uniformly oval.
DEC plugs: Desquamated epithelial cells sometimes form tiny plugs around hair follicles. They look like white dots near the scalp and can be confused with nits, but they’re attached to the skin rather than the hair shaft itself.

The quickest field test is to try to slide the suspect particle along the hair. If it glides freely, it’s not a nit. If it’s firmly cemented in place and requires a fingernail or fine-toothed nit comb to move, it probably is one. Shape matters too: real nits have a consistent oval or teardrop shape, while most lookalikes are irregular.

Why Visual Inspection Alone Misses Most Cases

If you’re checking a child’s head by simply parting the hair and looking, you’ll find a lot less than you think. A study comparing visual inspection to wet combing found that visual inspection caught only about 29% of active infestations, while wet combing caught roughly 91%.³ That’s a massive gap. The traditional method of parting dry hair under a bright light is better than nothing, but it misses the majority of live cases, especially when the infestation is light and only a handful of lice are present.

Wet combing works much better for a few reasons. Applying conditioner to wet hair slows the lice down considerably, making them less able to scurry away from the comb. The fine teeth of a proper louse comb (with tooth spacing of about 0.2 to 0.3 millimeters) physically trap lice and nits as you draw the comb through each section. You then wipe the comb on a white tissue or paper towel, where any lice or nits show up clearly against the background. A separate study comparing the two methods in schoolchildren found that traditional scalp inspection had a positive predictive value of about 0.70, meaning that roughly three in ten children flagged as infested by a visual check turned out not to actually have lice when wet combing was used as the reference standard.⁴ So visual inspection produces both false negatives and false positives at a concerning rate.

For parents checking at home, the practical takeaway is clear: use a fine-toothed metal nit comb on wet, conditioned hair, section by section, wiping the comb after each pass. Check behind the ears and along the nape of the neck, since lice tend to cluster in warmer areas with denser hair. A magnifying glass and good lighting help, but the comb does most of the work.

How Lice Move and Why It Matters for Identification

Lice move in a distinctive way that’s useful for identification. They crawl rather than jump or fly, gripping a hair shaft with their clawed legs and pulling themselves forward. Their movement is surprisingly fast for their size, which is part of why dry visual inspection fails so often. When you part the hair, live lice scramble away from the light and can vanish into surrounding strands in seconds.

Research on how lice transfer between hairs has shown that the transfer depends heavily on the angle and speed of hair contact. In lab experiments, the highest rate of lice moving from one hair to another occurred when hairs were oriented parallel to each other and moving slowly in a tail-to-head direction, with transfer rates reaching 85%. When hairs crossed at a 90-degree angle, no transfer was observed at all.⁵ This is consistent with the well-established understanding that head lice spread primarily through direct head-to-head contact, not through hats, pillows, or brushes. The geometry of how hair strands line up during prolonged head contact gives lice the slow, parallel-strand conditions they need to cross.

When you spot something on the scalp and aren’t sure whether it’s a louse, watch for movement. Even a tiny first-instar nymph will move, however slowly. Dandruff, hair casts, and product residue stay still. If the speck you’re looking at shifts position on its own, even slightly, treat it as a live louse until proven otherwise.

Body Lice and Pubic Lice Look Different

Head lice are only one of three species of lice that infest humans. Body lice and pubic lice are distinct species with different appearances, habitats, and behaviors, and confusing them can lead to the wrong treatment approach.

Body lice (Pediculus humanus corporis) look nearly identical to head lice in size, shape, and color. Telling them apart by appearance alone is genuinely difficult, even under a microscope. The difference is behavioral: body lice live in clothing seams, not on the body, and crawl onto the skin only to feed. You find their nits cemented to clothing fibers rather than hair shafts. If you see lice on the body of someone with poor access to clean clothing or laundry, the insects themselves may look just like head lice, but their location and nit placement give them away. Body lice are the only human louse that transmits disease, including epidemic typhus and relapsing fever, which head lice do not.

Pubic lice (Pthirus pubis), commonly called crabs, look quite different from head or body lice. They are shorter and broader, about 1 to 2 millimeters long, with a rounded, crab-like body shape and oversized claws on their second and third pairs of legs adapted for gripping the thicker, more widely spaced hairs of the pubic region, chest, armpits, and occasionally eyebrows or eyelashes. Under magnification, the crab louse egg has a complex cap structure with a system of tiny openings used for gas exchange.⁶ Pubic lice are transmitted through close body contact, usually sexual, and their nits are found cemented to coarse body hair rather than fine scalp hair.

The visual difference between head lice and pubic lice is obvious once you’ve seen both. Head lice are elongated and narrow, while pubic lice are squat and wide. Head lice are found exclusively on the scalp (with very rare exceptions in eyebrows or beards), while pubic lice stick to coarser body hair. If you spot small insects in the pubic area, don’t assume they’re the same thing as the head lice you’ve been reading about; the treatment and prevention considerations differ.

What Color Are Lice on Different Hair Types

A common question is whether lice look different on different people. The short answer is that the louse itself adapts its appearance somewhat to its host’s coloring, though not dramatically. Lice on people with very dark hair may appear slightly darker overall, partly because the contrast makes them harder to see and partly because their translucent exoskeleton picks up some pigment from the blood they consume and the environment. On light or blond hair, lice tend to look paler and more visible. But these are subtle shifts, not chameleon-level camouflage.

What does change meaningfully is how easy each life stage is to spot. Nits on dark hair tend to be more visible because their yellowish-tan color stands out against a dark background. On very light blond hair, nits can blend in almost perfectly. Conversely, adult lice are harder to see on dark hair (they’re small and dark-adjacent) and somewhat easier to spot on blond or red hair. This is another reason wet combing on a white background is the gold standard for detection: you take the color-matching problem out of the equation entirely by looking at what the comb picks up against a neutral surface.

When Old Nits Linger After Treatment

One of the most stressful experiences for parents dealing with lice is finishing a round of treatment and still finding nits in the hair. This is normal and doesn’t always mean treatment failed. Remember that the cement sheath bonding each nit to the hair shaft is extraordinarily durable, and dead or hatched nits stay glued in place long after the infestation is over. As hair grows at roughly a centimeter per month, old nits slowly migrate away from the scalp.

The key distinction is between nits close to the scalp and nits farther out. A nit more than about a centimeter from the scalp surface has almost certainly already hatched or died, because lice eggs need the warmth of the scalp to develop and they typically hatch within seven to ten days of being laid. Finding empty white casings several centimeters out along the hair shaft is evidence of a past infestation, not a current one. Finding plump, tan-colored nits right at the scalp line after treatment is more concerning and may warrant a second round of treatment or a different product.

Many school “no-nit” policies require children to be free of all nits before returning to class, which has been criticized by medical organizations including the American Academy of Pediatrics. The reasoning is straightforward: the presence of old, empty nit casings far from the scalp is not evidence of an active, transmissible infestation, and keeping children out of school over dead eggs causes unnecessary disruption without reducing transmission.

How Long Lice Have Looked This Way

Human head lice have been our companions for a very long time. Genetic evidence suggests that body lice, which live in clothing, diverged from head lice at least 83,000 years ago and possibly as far back as 170,000 years ago, which gives researchers a window into when early humans began wearing clothes.⁷ The oldest physical evidence of head lice comes from archaeological finds of nit casings on ancient hair samples, some dating back thousands of years and looking virtually identical to what you’d pull off a child’s head today.

Lice are extremely host-specific. Human head lice infest only humans. You cannot catch them from pets, and your dog or cat cannot catch them from an infested child. This specificity is part of why lice haven’t changed much: they’ve been evolving alongside us, adapting to human hair diameter, human scalp temperature, and human blood chemistry. The claw structure on each leg is precisely sized to grip a human scalp hair, which has a particular diameter range. Put a head louse on a strand of animal fur that’s the wrong thickness and it struggles to hold on. This tight coevolution means the basic body plan of a human head louse has been stable for tens of thousands of years, even as lice have developed resistance to various insecticides over more recent decades.