Lice in hair are tiny parasitic insects called head lice that live on the human scalp and feed on blood. They’re extremely common, especially in children ages 3 to 11, with an estimated 6 to 12 million infestations occurring each year in the United States alone. Head lice don’t carry disease, but they cause persistent itching and are notoriously difficult to get rid of without targeted treatment.
What Head Lice Look Like
Adult head lice are about the size of a sesame seed, roughly 2 to 3 millimeters long. They’re tan to grayish-white and have six legs with claws designed to grip individual hair strands. Because they move quickly and avoid light, spotting a live louse on someone’s head can be surprisingly difficult. You’re more likely to notice their eggs first.
Those eggs, called nits, are oval-shaped and attached firmly to hair shafts close to the scalp, where warmth helps them develop. Fresh nits are yellowish-brown and can look like tiny droplets stuck to the hair. Empty shells left after hatching appear white or clear. A common source of confusion is telling nits apart from dandruff. The simplest test: try to flick the speck off the hair. Dandruff slides off easily. Nits don’t, because the female louse cements each one in place with a glue-like substance.
The Life Cycle on Your Scalp
Head lice go through three stages, and understanding the timeline matters because it directly affects how you treat them.
- Egg (nit): Laid at the base of a hair shaft, nits take about one week to hatch, with a range of 6 to 9 days. They must stay close to the scalp’s warmth to survive.
- Nymph: Once hatched, the immature louse (nymph) goes through three molts over about 7 days before reaching adulthood. Nymphs look like smaller, paler versions of adults and begin feeding on blood almost immediately.
- Adult: A fully grown louse can live up to 30 days on a person’s head. Females lay several eggs per day throughout their lifespan, which is why an untreated infestation grows quickly.
This roughly six-week cycle, from egg to egg-laying adult, explains why a single treatment often isn’t enough. Eggs present on the day of treatment can hatch days later, starting the cycle again if they aren’t killed or removed.
How You Get Lice
Head lice spread almost exclusively through direct head-to-head contact. They cannot jump or fly. Their claws are built for gripping hair, not for hopping between surfaces. This is why lice spread so efficiently among young children, who tend to play in close physical contact, share pillows during sleepovers, or press their heads together over a screen.
Transmission through shared hats, brushes, or headphones is possible but far less common than most people assume. Lice need human blood to survive, and they dehydrate relatively quickly once separated from a scalp. Having lice has nothing to do with hygiene. Lice actually prefer clean hair because it’s easier to grip. They’re equal-opportunity parasites that affect every socioeconomic group.
Why Lice Make Your Head Itch
The itching comes from your body’s reaction to louse saliva. Each time a louse feeds, it injects a small amount of saliva into the skin to prevent blood from clotting. Your immune system recognizes this as a foreign substance and mounts an allergic-type response, which produces that familiar itch.
Here’s something that catches many people off guard: if you’ve never had lice before, it can take 4 to 6 weeks before the itching starts. Your immune system needs time to become sensitized to the saliva. That means a child could have a full-blown infestation for over a month before anyone notices. People who’ve had lice before tend to react much faster because their immune system already recognizes the trigger.
Beyond itching, you may notice small red bumps on the scalp, behind the ears, or along the neckline. Excessive scratching can break the skin and occasionally lead to a secondary bacterial infection, but the lice themselves don’t transmit illness.
How to Check for Lice
The best way to confirm an infestation is a systematic check with a fine-toothed comb, often called a nit comb. Wet the hair first and apply conditioner, which slows the lice down and makes them easier to spot. Section the hair and comb from the scalp outward, wiping the comb on a white paper towel after each pass. Live lice will appear as small, moving brown specks. Nits will look like tiny grains stuck to hair strands near the root.
Focus on the areas behind the ears and along the nape of the neck. These are the warmest spots on the scalp and where lice tend to congregate. In a light infestation, you may find only a few nits and no live lice on a given check, so be thorough. Good lighting helps enormously.
Treatment Options That Work
Treatment combines a product that kills live lice with manual removal of nits. Neither step alone is reliable enough on its own.
The two main over-the-counter options both target the louse nervous system. One is derived from chrysanthemum flowers and kills live lice on contact but has no effect on unhatched eggs. The other is a synthetic version of the same compound that also kills live lice and continues working for several days after application, catching some newly hatched nymphs. Neither product reliably kills all nits, which is why a second treatment is typically needed 7 to 10 days later to catch lice that hatch between treatments.
After applying any treatment product, use a fine-toothed nit comb to remove dead lice and as many nits as possible. Flea combs designed for cats and dogs work well for this too. Then check the hair and comb out any remaining nits and lice every 2 to 3 days for the next 2 to 3 weeks. This ongoing combing is one of the most important parts of treatment and the step most people skip too early.
When Over-the-Counter Products Don’t Work
In some areas, lice populations have developed resistance to the ingredients found in standard drugstore treatments. If you complete two rounds of treatment exactly as directed and still find live lice crawling on the scalp, the lice may be resistant. Prescription treatments work through different mechanisms and can be effective where over-the-counter options fail. Your pharmacist or doctor can help determine the next step.
Cleaning Your Home After Lice
Because lice can’t survive long without a host, you don’t need to fumigate your house or throw out furniture. Focus on items that had direct contact with the infested person’s head in the 48 hours before treatment. Wash bedding, pillowcases, and recently worn hats or scarves in hot water and dry on high heat. Soak combs and brushes in hot water (at least 130°F) for 5 to 10 minutes. For items that can’t be washed, sealing them in a plastic bag for two weeks will kill any lice or nits.
Vacuuming furniture and car seats where the person’s head rested is a reasonable precaution, but spraying insecticide around your home is unnecessary and not recommended. Your time and energy are better spent on thorough combing than on deep-cleaning every surface in the house.