Condition

Head Lice

Head lice are small insects that live on the scalp and glue their eggs to the hair. They spread through head-to-head contact, they do not carry disease, and they have nothing to do with how clean anyone is. Treatment clears them, but it almost always has to be repeated.
Dr. Schwarz, MD · Board-certified dermatologistLast reviewed September 8, 2026

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This is not a hygiene problem — head lice have no preference for dirty hair, and the embarrassment is why a lot of cases get treated in secret, badly, for months. The itch misleads people, because it is an allergic reaction to louse saliva that can take four to six weeks to develop the first time, so no itch does not mean no lice, and itching that carries on for a week or two after treatment does not mean the treatment failed. What tells you lice are still there is finding a live, moving louse — not the itch, and not eggs stuck to the hair. One treatment is rarely enough, because most products do not reliably kill eggs, so a second application about a week later is part of the plan, and if two proper courses have genuinely failed, the answer is a different medicine rather than a third round of the same one.

— Dr. Schwarz, Board Certified Dermatologist

Key Facts

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How commonVery common - millions of cases are treated in the United States each year, most of them in children aged 3 to 11
Who gets itAnyone with hair. Most cases are in young school-age children and the adults who live with them
Curable or managedCurable - treatment clears the infestation and lice do not stay in the body afterward
Prescription neededNot always. Over-the-counter treatments still work in many places, but resistance is common and there are several prescription options
Time to improveLice are usually gone after treatment plus a repeat about a week later. Itching can take one to two weeks to settle after that

What It Is

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Head lice are insects about the size of a sesame seed that live on the scalp and feed on small amounts of blood several times a day. The medical name is pediculosis capitis. An adult louse is gray-white to tan, darkens after feeding, and has six legs with claws built to grip a hair shaft. It cannot jump, fly or swim well. It crawls between hairs, which is why close head-to-head contact is how it spreads.

A female glues each egg to a hair shaft close to the scalp, where it is warm. The eggs are called nits — tiny, oval and firmly cemented on, which is how you tell them from dandruff, which flicks off, and hair casts, which slide along the shaft. An egg hatches in about a week to ten days, and the empty shell stays glued on and grows out with the hair. Nits more than about a quarter inch from the scalp are usually old shells, not live eggs.

Head lice live only on people. They do not come from pets, they do not live in carpets or gardens, and off a scalp they die within a day or two.

Three kinds of lice affect humans. Head lice live on the scalp and carry no disease. Body lice live in clothing, are linked to crowded conditions and limited access to laundry, and can transmit serious infections. Pubic lice, sometimes called crabs, are a different species spread by close body contact. Having head lice tells you nothing about the other two.

Symptoms

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Itch behind the ears and neck

Itchy Scalp

Itching, most noticeable behind the ears and at the nape, which starts weeks after lice arrive rather than immediately. Some people never itch at all. Itch alone does not confirm lice, so a comb-through is how it is checked.
Eggs stuck near the scalp

Nits on the Hair Shaft

Small oval eggs glued firmly to hair shafts, usually within a centimetre of the scalp, that will not slide off the way dandruff does. Empty shells stay stuck as the hair grows out. Only nits close to the scalp suggest a live problem.
Moving insects

Live Lice Seen

Gray-brown insects about the size of a sesame seed moving quickly near the scalp, easiest to find with a fine-toothed comb on damp, conditioned hair. Seeing one is what confirms an active case. Household contacts are usually checked at the same time.

Where It Shows Up

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Front view of a head with red marks across the scalp, at both sides above the ears and on both ears.
Behind the ears and at the nape
Lice stay on the scalp and keep close to the skin for warmth. The warmest spots are behind the ears and at the back of the neck, and that is where eggs are easiest to find, glued to hairs close to the root. They do not live on eyebrows, eyelashes or body hair.
Back view of a whole body with red marks on the back of the head, behind both ears and at the nape of the neck. The rest of the body is clear.
The back of the head
The nape of the neck is the single best place to look, because it is warm, it is where hair is thickest at the root, and it is the area someone else can see and you cannot.

What Happens in the Skin

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This is what is going wrong under the skin, in the order it happens. Click a step to see it.

How Head Lice happens
Skin basics
BARRIEREPIDERMISDERMIS0A NORMAL SCALP1LICE ARRIVE BY HEAD-TO-HEAD CONTACT2THEY FEED ON THE SCALP3EGGS HATCH INTO A NEW GENERATION4THE ALLERGIC ITCH AND SCRATCHING

Hair and scalp with nothing living on them.

Lice cannot jump or fly. They crawl from one head to another when heads touch, which is why it runs through classrooms and families rather than through hats.

An adult louse bites the scalp for blood several times a day and lives about a month. It cannot survive more than a day or two away from a head.

Eggs are glued to hairs near the scalp and hatch in about a week. This is why treatment is repeated - the first round rarely kills eggs.

The itch is an allergic reaction to the saliva, and it can take weeks to start, so an infestation is often well established before anyone notices. Scratching breaks the skin and can let bacteria in.

The outer film of dead cells and oil. It holds water in and keeps irritants out, and it is thinner than a sheet of paper. Almost every dry, itchy, stinging skin problem starts here.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

Four things happen, in order. A louse crawls from one head to another during direct, sustained head-to-head contact — children sitting shoulder to shoulder, sharing a pillow, taking photographs together, playing on the floor. It cannot jump or fly, so the hairs have to touch. On the new scalp it feeds on tiny amounts of blood several times a day, favoring the warm areas behind the ears and at the nape. Within a day or two the female starts laying eggs, gluing each to a hair shaft near the scalp where the temperature suits it. Those eggs hatch in about a week to ten days into young lice that mature in another week and lay their own.

The itch comes later and is a separate process — an allergic reaction to proteins in louse saliva, not a bite that hurts. The first time, that allergy can take four to six weeks to develop, which is why an infestation is often weeks old before anyone notices. Someone who has had lice before itches within days.

The hatching cycle is why treatment is repeated. Most products kill lice far more reliably than eggs, so one application leaves a generation still developing. A second application, timed after those eggs hatch but before the new lice can lay, is what ends it.

Risk Factors

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Head lice are about contact and opportunity, not cleanliness, income, housekeeping or how often hair is washed. Believing otherwise is the main reason families hide them.

Close contact
Living with someone who has them
The highest-risk exposure there is. Check everyone in the household when one person is diagnosed.
Close contact
Sleepovers, shared beds and naps
Prolonged head contact lying down moves lice efficiently.
Close contact
Crowded sleeping arrangements
More head contact during sleep, when much of the spread happens.
Age & family
Being a child aged 3 to 11
Much the most common group, because of how young children play — heads together, close, often.
Age & family
Parents and caregivers of young children
Adults get lice mostly from their own children.
Shared items
Sharing hats, brushes and combs
Headphones and pillows too. Less common than direct contact, but real.
Hair & history
Having long hair
Slightly more surface for contact, though lice manage on short hair perfectly well.
Hair & history
A previous infestation
No protection at all. Reinfection from the same untreated friends or family is common.

Course

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Left alone, head lice do not clear. They cause no lasting damage; the problems come from scratching, and occasionally infection on top.

ArrivalDay 0
Nothing is felt and nothing is visible

A louse or two crawl across during head contact.

Eggs and hatchingDays 1 to 10
Eggs are glued to the hair

The female glues eggs to hair shafts near the scalp within a day or two. The first hatch around day 7 to 10. Empty shells stay glued on and grow out.

Behind the earsThe nape of the neck
Building upWeeks 2 to 3
Numbers rise steadily

The new lice mature and lay their own eggs.

The itchWeeks 4 to 6
The scalp starts itching

In a first infestation the allergic reaction to louse saliva finally develops. Someone who has had lice before itches within days.

Back of the scalpBehind the ears
TreatmentDay 1, then day 8 to 10
The second application is the one people skip

The first kills live lice; eggs often survive. The second catches the generation that hatched after it. Itching can carry on one to two weeks after the last louse, because the allergy takes time to fade. Months of failed treatment is more often a social and emotional problem than a medical one.

What Makes It Better & Worse

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Head lice is not one problem, it is four — lice arriving, lice feeding, eggs hatching into a new generation, and the itch that follows. Lice get killed and eggs do not, so almost every case that drags on is failing at step three.

What is driving yours?

FATBARRIEREPIDERMISDERMIS

Lice cannot jump or fly. They crawl from one head to another when heads touch, which is why it runs through classrooms and families rather than through hats.

An adult louse bites the scalp for blood several times a day and lives about a month. It cannot survive more than a day or two away from a head.

An adult louse bites the scalp for blood several times a day and lives about a month. It cannot survive more than a day or two away from a head.

Eggs are glued to hairs near the scalp and hatch in about a week. This is why treatment is repeated - the first round rarely kills eggs.

What helps

  • Check every household member Same day, treating those with live lice.
  • Tell the school and close families The most effective way to stop the cycle.
  • Wash recent bedding and hair items Hot water and high heat, last two days.
  • Skip the deep clean of the house Lice die within a day or two off a scalp.
  • Keep long hair tied back A small measure, and an easy one.

What makes it worse

  • Not checking everyone at home One untreated head reseeds the rest.
  • Sharing hats, brushes and combs Headbands and headphones too.
  • Hiding it A group of children can pass it around for a term.

What helps

  • An over-the-counter treatment Permethrin or pyrethrin, exactly as the leaflet says.
  • Switch medicine after two courses Prescription options work differently.
  • Wet combing with a fine-toothed comb With conditioner, every three to four days for two weeks.

What makes it worse

  • Repeating the same product again After two courses it is resistance, not technique.
  • Applying treatment to wet hair Water dilutes it, and too little misses the back.
  • Conditioner just before treatment It coats the hair and blunts some products.
  • Washing the hair too soon after Some treatments keep working a day or two.
  • Kerosene, gasoline or bleach Dangerous — burns, poisoning and fires have resulted.

What helps

  • Repeat a week to ten days later Non-negotiable, because eggs survive.
  • Check again after the second treatment Look for live moving lice, not nits.

What makes it worse

  • Skipping the second treatment Most products do not kill eggs.
  • Treating on nits alone Empty shells stay glued on for months.

What helps

  • Treat the itch while it settles A gentle shampoo, antihistamine at night if needed.

What makes it worse

  • Scratching Breaks the skin at the nape, lets infection in, leaves lasting marks.

How These Treatments Work

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Treatments for Head Lice do not all work in the same place. Tap one to see where it acts.

Pick a treatment
Skin basics
BARRIEREPIDERMISDERMISKILLS THE LICEREMOVES LICE AND EGGSCATCHES THE HATCHLINGSSTOPS IT COMING BACKTHE ITCH LINGERS

Kills the live lice on the hair. Most products do not kill the eggs.

Mechanical, and the part most often skipped.

Eggs that survived the first round hatch seven to nine days later.

Other people in the house are usually how it returns.

A reaction that fades over days. It does not mean treatment failed.

The outer film of dead cells and oil. It holds water in and keeps irritants out, and it is thinner than a sheet of paper. Almost every dry, itchy, stinging skin problem starts here.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

Over-the-Counter Products

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Everything here you can buy without seeing anyone.

16:9 hero for Permethrin. Never cropped: the tone strip and the corner logo depend on the full frame.Diagram: how Permethrin works in the skin
Moderate evidence
The usual first treatment, applied to dry hair, left the stated time and rinsed, then repeated in seven to ten days because it does not reliably kill eggs. Where lice are not resistant it works well. Resistance to it is now common in many areas, so if two proper courses fail, the answer is a different medicine, not a third round.
Three cream tubes on white: Nurture Valley Barrier Cream, Secura Dimethicone Protectant and Medline Remedy Moisturize16:9 hero for Dimethicone. Never cropped: the tone strip and the corner logo depend on the full frame.
Moderate evidence
A silicone lotion that coats and suffocates the lice rather than poisoning them, so resistance is not an issue with it. It is left on for the stated time — often several hours or overnight — and repeated a week later. It is a good option for a child who has already failed permethrin, and it is gentle on the scalp.
Wet combing with a nit comb
Wet combing with a nit comb
Moderate evidence
Wet the hair, work in plenty of conditioner so the lice cannot grip, and comb section by section from scalp to ends with a fine-toothed metal comb, wiping onto a white paper towel after each stroke. Repeated every three to four days for two weeks it can clear an infestation on its own, and it is how the diagnosis is confirmed either way. It works, but it takes real time and it has to be done properly.
Pyrethrin shampoo
Pyrethrin shampoo
Limited evidence
The other older over-the-counter option, from chrysanthemum extract, used the same way with a repeat in seven to ten days. It kills fewer eggs than permethrin does and lice are commonly resistant to it. It is avoided in anyone with a ragweed or chrysanthemum allergy.
Smothering with oils
Smothering with oils
Weak evidence
Mayonnaise, olive oil and petroleum jelly left on overnight are popular, messy and barely studied. They may kill some lice, they do not deal with the eggs, and they are not a substitute for a treatment that has been tested. Kerosene, gasoline and bleach are a different matter — they are dangerous and have caused burns, poisoning and fires, and must never be used.
Five dark glass tea tree essential oil bottles with glass droppers and one green box on white16:9 hero for Tea Tree Oil. Never cropped: the tone strip and the corner logo depend on the full frame.
Weak evidence
Sold in several natural lice products and not shown to clear an infestation reliably. It irritates the scalp of a child who is already scratching, and it is a common cause of allergic reactions. If the older products have stopped working, a prescription treatment is a better answer than an essential oil.

Prescriptions

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These need a prescription.

A white cream tube lying on its side on a white background, with a plain white label reading Ivermectin and a blue swoosh beneath it.
Ivermectin lotion 0.5%
Strong evidence
A single ten-minute application to dry hair, and usually no repeat is needed, because it kills the young lice as they hatch. That makes it a good choice for families who have already skipped or fumbled a second application. It is one of the main options when permethrin has failed.
A white shampoo bottle on a white background, with a plain white label reading Spinosad and a blue swoosh beneath it.
Spinosad suspension
Strong evidence
A ten-minute application to dry hair that kills both lice and most eggs, so a second treatment is often unnecessary. High cure rates in studies against permethrin-resistant lice. Cost and availability are the usual limits rather than how well it works.
A white cream tube lying on its side on a white background, with a plain white label reading Malathion and a blue swoosh beneath it.
Malathion lotion
Moderate evidence
An older prescription lotion that kills lice and many eggs, applied to dry hair and left on for the stated time. It works where permethrin has failed. It smells strongly, it is flammable while wet so no hairdryers, flames or cigarettes near it, and it is not used in young children.
A white cream tube lying on its side on a white background, with a plain white label reading Benzyl Alcohol and a blue swoosh beneath it.
Benzyl alcohol lotion
Moderate evidence
It works by blocking the breathing holes of the lice rather than poisoning them, so resistance is not expected. It does not kill eggs, so the repeat in seven days is essential. It can sting and irritate the scalp, which matters if the skin is already scratched.
A white cream tube lying on its side on a white background, with a plain white label reading Lindane and a blue swoosh beneath it.
Lindane
Never use
An old prescription shampoo that is no longer recommended for head lice. It is less effective than the current options and has caused seizures when overused or used on broken skin. It is included here only because people still come across it — there is no situation now where it is the right choice.
An amber prescription bottle lying on its side on a white background with a plain white label reading Ivermectin, and six small round white tablets spilled out in front of it.
Ivermectin tablets
Moderate evidence
A tablet taken as two doses about a week apart, used when repeated topical treatments have failed or when applying a lotion to the whole scalp is not practical. It is effective in that situation. It is not used in small children or in pregnancy, so the prescriber checks weight and circumstances first.

Procedures

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These are done in the office, usually over several visits.

No procedures listed yet.

When to See a Dermatologist

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Most head lice never need a dermatologist — a pharmacy treatment and a comb handle it at home. Book if two properly applied over-the-counter courses have not worked, which usually means resistance, or if you are unsure it is lice, because dandruff, hair casts, product residue and scalp eczema all get mistaken for nits. Ask to be seen sooner if the scalp or neck is red, swollen, weeping or crusted, if the neck glands are tender, if the child is under two months old, if there is eczema, psoriasis or broken skin on the scalp, or if asthma or a known allergy rules out certain treatments; ask your doctor before treating if you are pregnant or breastfeeding. The standard is finding a live louse, by wet combing with conditioner and a fine metal comb, because nits are not enough — empty shells stay glued on for months after an infestation ends.

— Dr. Schwarz, Board Certified Dermatologist

Complications

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Infected scalp and neck

Scratching breaks the skin, and bacteria can get in on top. The signs are redness and swelling that spreads, weeping or honey-colored crusts at the nape and behind the ears, and tender glands in the neck. It is the main reason a case of lice ever needs antibiotics, and it needs to be seen. Treating the lice properly and settling the itch early is what prevents it.

Weeks of broken sleep and worry

The lasting harm from head lice is rarely medical. It is the itching that keeps a child awake, weeks of repeat treatments and combing, missed school where old exclusion policies are still used, and the embarrassment that makes families treat it in secret. Telling the school and the other families is the single most effective thing for ending the cycle, and it is the step people most want to skip.

Lookalikes

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Dandruff

This is the mix-up that sends most families to the pharmacy. Both leave small white specks in the hair. Dandruff flakes sit loose, flick off easily and are irregular in shape; nits are oval, glued to one side of a hair shaft and will not slide or brush off. If it moves when you push it, it is not a nit.

Seborrheic Dermatitis

It gives an itchy scalp with flaking, so it gets treated as lice more than once. The scale is greasy and yellowish, it sits in patches on visibly pink, irritated skin along the hairline and behind the ears, and it comes and goes for years. Lice give you eggs stuck to hair shafts and, eventually, a live insect on the comb.

Scalp Psoriasis

Another itchy, flaking scalp that gets treated as lice first. Psoriasis makes thick, well-defined raised plaques with silvery scale that often cross the hairline onto the forehead or behind the ears, and it stays in the same places for months. Nothing is stuck to the hair shafts, and there is no live insect to find.

Myths

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  • "Head lice mean poor hygiene." They do not Lice need hair and a scalp, and do fine on freshly washed hair. Infestations happen in every kind of household, and believing they signal neglect is why families hide them.
  • "Lice can jump or fly from one person to another." They cannot. No wings, no jumping. They crawl, which is why spread needs sustained head-to-head contact, not sitting near someone.
  • "You can catch them from your dog or cat." Head lice live only on humans. Pets do not carry them.
  • "The whole house has to be fumigated." It does not. Lice die within a day or two off a scalp. Wash recently used bedding and hats, vacuum the sofa, and stop — home insecticide sprays are unnecessary and not recommended.
  • "No itching means no lice." The itch is an allergic reaction to louse saliva, and in a first infestation it can take four to six weeks to develop. Plenty of children have lice for a month before anyone notices.
  • "Finding nits means the lice are back." Empty shells stay cemented to the hair for months. Nits more than about a quarter inch from the scalp are old shells. What matters is finding a live, moving louse.
  • "Children with lice must be kept off school until every nit is gone." Major pediatric and public health bodies advise against no-nit exclusion policies. Lice spread slowly, a child has usually had them for weeks, and missing school does more harm than the lice.
  • "Mayonnaise or olive oil overnight will smother them." Petroleum jelly gets the same claim. Popular, largely untested and messy. They may kill some lice, they do not deal with eggs, and they do not replace a studied treatment. Kerosene, gasoline and bleach are dangerous and have caused serious burns.

Questions Patients Ask

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How did my child get them?

Almost certainly direct head-to-head contact with another child — playing on the floor, a sleepover, photographs head to head. Not the house, the pets or anyone's hair. By the time you find them the contact was weeks ago.

Does my child have to stay home from school?

Major pediatric and public health bodies advise against sending children home for lice. By the time they are found they have usually been there for weeks, and lice do not spread easily in a classroom. Tell the school, start treatment, and in most places the child stays. Check your school's policy — some are stricter than the guidance.

Do I have to get every nit out?

No. It makes future checks easier and reassures everyone, but empty shells are harmless and grow out. What matters is that no live lice remain. Combing with conditioner and a metal comb beats picking them out dry.

Why is my child still itching after treatment?

Because the itch is an allergic reaction, not the lice, and takes one to two weeks to settle after the last louse is gone. The scalp has also been scratched and treated with something drying. Itching alone is not a reason to treat again. Finding a live louse is.

Do I need to treat everyone in the family?

Check everyone the same day and treat the ones with live lice. Some doctors also treat anyone who shares a bed, even with no live lice found, because that contact is so close. Treating the whole household regardless is not recommended.

Why did the treatment not work?

In order of likelihood: the second application was skipped, the product was misused, someone else in the house was not treated, reinfection came from the same friend or classroom, or the lice are resistant. Only the last is a reason to change medicine, so work through the other four first.

References

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