You followed the directions. Ten minutes, rinse, comb. You stripped the beds and bagged the stuffed animals. You put the second treatment on the calendar for day 9.

And you just found a live one on the comb.

If that's where you are, this is the page we wish somebody had handed us in the pharmacy aisle. Nothing here is about doing it "more carefully." You were careful.

The box was the problem, for five specific reasons, and every one of them has a fix that a lice-removal technician uses on other people's kids every day.

Nix is permethrin. The RID most of us grew up with is pyrethrin. They're related insecticides, and lice have been exposed to them since the 1980s.

That's a long time for a bug to adapt.

In 2016, researchers tested lice collected from 48 states and found the resistance gene in 42 of them, at very high frequency.¹ That is why a family can do two full rounds by the book and still find a live louse on the comb: most lice don't die from that poison anymore.

The cheap lice kits on Amazon, the ones with thousands of reviews and a $16 price, are mostly the same chemical with a different label. Families switch brands three times and buy the same thing three times.

Those little tan dots stuck to the hair near the scalp, the ones that won't slide off no matter how you pull the comb, are eggs. Each one is glued to a single hair and sealed inside a hard protein shell.

The poison can sit on that shell for the full ten minutes. It can touch the egg. It cannot kill what's inside. About a week later, the eggs hatch.²

That is what the "repeat in 9 days" line on the box means. It isn't a second treatment for safety. It's the manufacturer telling you the first one won't get the eggs, so come back when they've hatched and try to catch the babies.

So the lice you found on day 9 weren't new lice. They were the same lice, from eggs the shampoo was never going to kill.

This is the one almost nobody tells you, and it's the one that keeps families in the loop for a month.

You lose 50 to 100 hairs a day.

So does every person in your house.³ When someone has lice, some of those hairs have an egg glued to them, and those hairs land where your kids sit and sleep: the couch, the car seat, the pillowcase, the headrest, the hoodie she wears three days in a row.

Everyone knows a louse can't live long off a head. The eggs are a different story.

In lab tests, lice eggs kept off the head in a warm room hatched about 12 days later, 8 out of 10 of them.⁴ A couch cushion with a seven-year-old sitting on it is a warm room.

So a clean, combed, exhausted kid finishes treatment and sits back down on the same couch. That is where it keeps coming from. Yes, kids also pick it up again at school. But most of the time, the lice that "come back" never left.

The comb that comes with Nix or RID is plastic, with teeth spaced for hair, not for eggs. An egg is about the width of a hair glued to a hair. A plastic comb slides over it.

You can comb for an hour a night and leave most of them in place, which is exactly what most families do.

Then there's seeing them. A nit is tan and translucent and the size of a poppy seed, on a moving child, under a bathroom light. Lice-removal technicians don't work under a bathroom light.

They use a metal comb with tightly spaced teeth, and an ultraviolet flashlight, because lice and nits are easier to see under ultraviolet. That's how they know they're done instead of guessing for a month.

One box treats one head. So the child with the note from the nurse gets treated Tuesday, her sister starts scratching Thursday, and Dad "definitely doesn't have them" until week three. Every head that's treated on a different night is a head that can hand it right back.

The new RID One & Done makes this worse in a way that's easy to miss. It's a real change from the old RID: it's ivermectin, a different drug that kills lice the old poison can't.

The purple box says ONE TIME, NO NIT COMBING, 10 MINUTES, and it costs a little over $40 for one tube. One tube treats one head.

It doesn't claim to do anything about the eggs, it can't do anything about eggs that aren't on a head anymore, and it says nothing about the couch. For a family of four that's four tubes, about $168, and you're still exactly where reason 3 left you.

Put the five reasons together and the fix writes itself. Stop trying to poison something that doesn't die from poison. Go after the glue. Treat every head and the environment on the same night.

Use a comb that can actually grab an egg and a light that lets you see one.

The technicians we talked to for this piece use a two-step treatment built for exactly that. Step one is an enzyme that dissolves the glue holding each egg to the hair and softens the shell of the bug itself.

It's a physical action, like sugar dissolving in water, which is why a louse can't "get used to it" the way it got used to Nix. Step two is a blend of plant oils, clove, neem, peppermint and eucalyptus, that finishes what's left. No permethrin.

Then the house, the same evening: a spray for the couch, the car seats, the beds and the pile of hoodies, and a laundry concentrate for every load. A metal comb. An ultraviolet flashlight to check every head every night for the next week, so you know you're actually done.

The one the technicians we spoke with use is the Everything You Need Kit from LiceKiller, a family company that has made the enzyme and oil treatment since 2004.

The kit is sized for every head in your house, and it includes the spray for furniture, cars and bedding, the metal comb, and the ultraviolet flashlight. Every fix on this page is in the box.

It's a little over $150. That is more than a bottle of Nix, and you should know that before you click. Here is the math the way the mothers who wrote to us did it: two or three drugstore boxes, $60 to $112, already gone.

The new RID at over $40 a head. A lice clinic at $125 to $250 per child, and you still do the couch yourself. A lice service that comes to your house, about $450 for a family of four.

The kit is less than one child at the clinic, and it does the house.

More than 100,000 families have used it. Their refund rate is less than one percent. A lice-removal expert demonstrated it on ABC's Nightline, and there's a money-back guarantee in writing on their site, next to the button.

The Nit Glue Dissolver goes on dry hair, scalp first, section by section, then a shower cap for thirty minutes. You don't rinse. The oils go on over the top, every strand, no dry spots, and the cap goes back on for another half hour.

Then you comb, scraping along the scalp one section at a time, and the eggs that survived weeks of Nix come off the hair on the first pass.

Mothers tell us the same thing over and over: they wiped the comb on a paper towel, saw the row of eggs, and that was the moment they knew it was over.

Every head in the house gets treated the same night, including the parent who swears they don't have them.

While the caps are on, you do the house: the Furniture Spray on the couch cushions, the car seats, the pillows and the mattresses, and the Laundry Concentrate in a load of sheets and hoodies. About twenty minutes.

The combing still takes a while. Long hair, an hour, no way around it. But every head and the whole house get done in one evening, and then you check every head with the ultraviolet flashlight every night for a week instead of guessing for a month.

A louse lays about six eggs a day. Each one hatches in about a week. Every night you wait, the number of eggs in your house goes up, on heads and off them. The second box doesn't change that.

Neither does the $42 purple one, and neither does the one from Amazon.

If you order before 4:45 PM Eastern (1:45 PM Pacific), the kit ships today and it's on your porch in two business days, free. You do every head and the house that evening, and you check every head with the ultraviolet flashlight every night for a week.

Two business days from now, this is either over or it's another week further along. That's the whole decision.

Why didn't Nix or RID kill my child's lice?

Nix is permethrin and classic RID is pyrethrin, related insecticides lice have been exposed to for about forty years. Researchers found the resistance gene in lice from 42 of 48 states. Most cheap Amazon kits use the same chemical.

RID One & Done is ivermectin, a different drug, applied to one head once; it does nothing for eggs already shed onto furniture and bedding.

Do lice shampoos kill the eggs?

No treatment reliably kills what is inside a nit. The poison can touch the shell but cannot kill the louse inside. Eggs on the head hatch in about 6 to 9 days, which is why boxes tell you to treat again in 9 days.

Can lice eggs on a couch or car seat hatch?

The CDC says nits away from scalp temperature usually don't hatch. In lab conditions, eggs kept off the host at 77–83°F hatched at about 81%, starting around day 12. People shed 50 to 100 hairs a day onto couches, car seats and pillows that can reach those temperatures.

What does a lice-removal technician use instead?

An enzyme that dissolves the glue holding each egg to the hair, then plant oils, a metal nit comb, an ultraviolet light to check for missed bugs and nits, and a spray for furniture, car seats and bedding. Every head and the environment are treated the same evening.

How much does a whole-family kit cost?

The LiceKiller Everything You Need Kit runs a little over $150 with free 2-business-day shipping and includes the comb and the ultraviolet light. A lice clinic typically charges $125 to $250 per child.

The Everything You Need Kit, sized for your family, with the comb and the ultraviolet light in the box. Free 2-day FedEx. The guarantee, in writing, right next to the button.

P.S. If your school has a no-nit policy, the ultraviolet light in the kit is how you know your child is clear before the nurse checks, instead of guessing.

Editor's notes and sources

1. Gellatly KJ et al., "Expansion of the knockdown resistance frequency map for human head lice in the United States," Journal of Medical Entomology, 2016 — kdr resistance alleles found in lice sampled from 42 of 48 states, at very high frequency.

2. CDC, "About Head Lice": nits take about a week (6–9 days) to hatch on the head. cdc.gov/lice.

3. American Academy of Dermatology: it's normal to shed 50 to 100 hairs a day. aad.org.

4. Sonnberg S et al., "Ex vivo development of eggs from head lice," Open Dermatology Journal, 2010: eggs incubated off the host at 77–83°F hatched at 80.9%, with hatching beginning at a median of 12 days. Leeson HS, Parasitology, 1941: louse eggs hatch at temperatures down to about 75°F and not below. The CDC's position is that nits away from scalp temperature usually do not hatch; the studies above describe what happens in warm conditions.

Nix and RID One & Done are trademarks of their respective owners and are not affiliated with this site. Prices quoted are typical retail prices and vary by store. Mothers Against Head Lice is a reader-supported site. Individual results vary; this page is not medical advice.