When nothing seems to work on head lice, stop repeating the same product and work out which of five specific things is going wrong, because the CDC’s list of reasons lice treatment fails is short. Then talk to your child’s doctor before another application. The AAP says to ask the doctor when the treatments you have tried have not gotten rid of lice, and your child may just need the same medicine again, or a different one. Nothing on that list is about how hard you have scrubbed.
It matters because every extra round is another dose of insecticide on a child’s scalp. The CDC describes the drugs used to treat lice as insecticides that can be dangerous if misused or overused. Getting the diagnosis and the timing right is what ends this, not more effort.
Why Will Lice Not Go Away When You Have Tried Everything?
Lice outlast repeated treatment for one of five reasons, and the CDC names all five in its guidance on treating head lice.
- Misdiagnosis, meaning what is being treated is not live head lice
- A combination shampoo/conditioner, or conditioner, used on the hair before the lice medicine
- Treatment instructions not followed
- Head lice resisting the medication
- Reinfestation after successful treatment
Two of those you can rule out tonight. The CDC says misdiagnosis of head lice infestation is common, and that nits are often confused with dandruff, hair spray droplets and dirt particles, which is why the AAP’s rule is to use head lice medicine only when it is certain that your child has living head lice. The conditioner problem is quieter. The CDC says not to use a combination shampoo/conditioner, or conditioner, before using lice medicine, and it notes that shoulder-length hair or longer might need a second bottle, which is one way a full course ends up under-applied.
Live Lice or Leftover Nits: What You Are Actually Looking At
A live, crawling louse is what tells you the infestation is still active. The CDC says finding a live nymph or adult louse on the scalp or hair is the best way to diagnose head lice, and that nits may stay in the hair after treatment while successful treatment kills crawling lice. Where the nits sit matters too. Nits attached more than one quarter inch from the base of the hair shaft are almost always hatched or dead, the CDC says, and if the only nits you find are farther than one quarter inch from the scalp, the infestation is probably old and does not need treatment.
Two things fool parents here. Live lice are hard to find because they avoid light and move quickly, so the AAP has you seat your child in a brightly lit room and part the hair a section at a time; the CDC adds that a magnifying lens may help. Itching is the second trap, because it lags behind the problem. The AAP says itching caused by head lice can last for weeks, even after the lice are gone, and the CDC explains that the itch is an allergic reaction to louse bites. Judge the result by what is moving on the scalp.
Does Your Medicine Kill the Eggs? That Decides the Second Round
Whether you need a second application depends on whether the medicine kills eggs as well as lice. The CDC says some medicines kill lice and eggs, and retreatment is usually not required for those, while others kill lice but are not effective at killing eggs, so retreatment is recommended. In that second case it says to treat again about a week after the first treatment, seven to nine days depending on the drug, after all the nits have hatched but before new eggs are produced. That window exists because nits take about a week to hatch, a range of six to nine days, and nymphs take about seven days to mature.
The CDC’s clinical guidance describes each active ingredient it lists. Read your label against it.
| Active ingredient | What the CDC says it kills | Who the CDC says it is for |
|---|---|---|
| Permethrin lotion, 1% | Kills live lice but not unhatched eggs; can kill newly hatched lice for several days | Children two months of age and older |
| Pyrethrins with piperonyl butoxide | Can only kill live lice, not unhatched eggs | Children two years of age and older |
| Benzyl alcohol lotion, 5% | Kills lice but does not kill eggs | People six months of age and older |
| Malathion lotion, 0.5% | Kills live lice and some lice eggs | People six years of age and older |
| Ivermectin lotion, 0.5% | Kills lice but not eggs; appears to prevent newly hatched lice from surviving | People six months of age and older |
| Spinosad 0.9% topical suspension | Kills live lice as well as unhatched eggs, so retreatment is usually not needed | Children six months of age and older |
Across its guidance the CDC ties the second round to two things: what the drug kills, and whether live lice are still there seven to nine days later. MedlinePlus says that if an over-the-counter treatment does not work for you, you can ask your health care provider for a prescription product, and the AAP says to check with your child’s doctor before beginning any head lice treatment.
What to Do When the Medicine Is Not Working
Call your child’s doctor instead of reaching for another application. The CDC says to talk to a healthcare provider before re-treating, and that they may suggest a different medicine. The AAP is firmer about repeats: check with your child’s doctor before beginning a second or third medicine. The limits the CDC sets out are worth knowing before you decide anything.
- Do not treat with the same medication more than two or three times if it is not successful
- Do not use different head lice drugs at the same time unless a healthcare provider or pharmacist tells you to
- Do not use extra amounts of any lice medication unless your physician and pharmacist instruct it
- If crawling lice are still present after a full course of treatment and retreatment, consider an alternative medication
There is a reason to make that call sooner rather than later. The AAP’s review of head lice treatment myths says over-the-counter treatments sometimes are not the most effective, and that parents sometimes treat their children up to five times before seeking help from their pediatrician. If you are on round three at home, you are already in that pattern. A professional screening is the other way out, and our guide to what to expect at a professional lice treatment clinic walks through a visit start to finish.
When the Comb Is Not Getting the Nits Out
Combing is how you check and how you clean up, but the AAP says the comb-out method usually does not work on its own to get rid of head lice. It also sets out the method: wet the hair, comb through small sections with a fine-tooth louse or nit comb, wipe the comb on a wet paper towel after each pass, examine the scalp, comb and towel, then repeat until all the hair is combed. MedlinePlus adds the detail that makes it work, which is parting the hair all the way down to the scalp in very small sections.
If the comb seems to be doing nothing, check three things. Nits are held on with a sticky substance, so a particle that slides off was never a nit. The eggs that matter sit close in, and the AAP says eggs are usually found within four to six millimeters of the scalp and do not survive farther away. And the schedule is longer than one night: the CDC says that after each treatment you check the hair and remove nits and lice every two to three days for the next two to three weeks. It also says flea combs made for cats and dogs are effective for this.
Not every medicine requires it. The CDC says nit combing is not required with spinosad topical suspension, and the AAP notes that some prescription products do not call for nit combing at all, though removing nits may help decrease embarrassment for a child or teen. If sitting still is the hard part, here is how to keep your child calm during lice treatment.
Why Lice Keep Coming Back After a Treatment That Worked
When live lice turn up again after a treatment that worked, the next place to look is the heads around your child. The CDC says head lice mainly spread by direct contact with the hair of a person who has them, and that lice move by crawling and cannot hop or fly. It also says to check all household members and other close contacts, and to treat everyone infested, including anyone they share a bed with, at the same time. Treating one child while an untreated sibling or adult carries lice restarts the clock, and the CDC notes that people with head lice may not have symptoms, particularly with a first or light infestation.
- Wash and dry the clothes, bedding and items used in the two days before treatment, using hot water at 130 degrees Fahrenheit and high heat drying
- Seal anything you cannot wash or dry clean in a plastic bag for two weeks
- Soak combs and brushes in hot water of at least 130 degrees Fahrenheit for five to ten minutes
- Teach children to avoid hair-to-hair contact during play and not to share combs, brushes, towels, hats, hair ties or helmets
Keep that work in proportion. The CDC says lice will die within two days if they fall off a person and cannot feed, and that the risk of getting lice from a louse that has fallen onto a rug, carpet or furniture is very small. Spending much time and money on housecleaning, it adds, is not necessary to avoid reinfestation.
Frequently Asked Questions
Can lice become resistant to a treatment?
Yes, in some places. The AAP says head lice can be resistant to the active ingredients in over-the-counter treatments in some communities. The CDC says lice have developed some resistance to one percent permethrin, and that the efficacy of pyrethrins may be reduced by resistance, while adding that how widespread either is remains unknown.
Why did a treatment that worked before stop working now?
Head lice resisting the medication is one of the five reasons the CDC lists for treatment failing, and the AAP says the likelihood of resistance varies across the country. One older ingredient, lindane, is no longer available in the United States or Canada because of its risk for severe side effects, and the AAP no longer recommends it. Your pediatrician can help you choose an appropriate option.
How long should it take to tell whether the medicine worked?
Judge it in hours, not minutes. The CDC says it takes time to kill all the lice, and that a few lice still moving slowly eight to twelve hours after treatment do not call for another application. If you find no dead lice, or they seem as active as before, the CDC says the medicine may not be working. Do not re-wash the hair for one to two days afterward.
Can a child have head lice without itching?
Yes. The CDC says it may take four to six weeks for itching to appear the first time a person has head lice, and the AAP says the same about the scalp becoming sensitive to lice saliva. A child can carry and pass on lice through that stretch without complaining once, which is why the AAP recommends regular checks to spot lice before they have time to multiply.
Do mayonnaise, olive oil or other home remedies kill lice?
There is no scientific evidence that they do. The CDC says it has no scientific evidence that suffocating head lice with mayonnaise, olive oil, margarine, butter or similar substances works, and the AAP says the same about petroleum jelly, essential oils and tub margarine, because no studies prove they work. Never use gasoline or kerosene, which are dangerous and flammable. Our rundown of natural head lice treatment options sorts out what is supported.
Should you treat the house when lice keep coming back?
No. The CDC says fumigant sprays and fogs are not necessary to control head lice and can be toxic if inhaled or absorbed through the skin, and the AAP says not to spray pesticides in your home. The CDC does suggest vacuuming the floor and furniture where the infested person sat or lay, and staying off bedding, couches, pillows and stuffed animals that an infested person has just used.
When You Are Ready to Hand It Off
If you have been through a full course and a retreatment and lice are still crawling, let someone else take the comb. Our clinics check the whole household, treat with a non-toxic, enzyme-based solution that is safe for children and carries 99.9% efficacy, and finish the comb-out strand by strand, same-day and in one visit, with our certified technicians doing the part that is hardest to complete at home. Treatment is backed by our 30 Day Guarantee, which applies when the whole family is checked, and you can read how long a lice treatment visit takes before you book. Find a Lice Lifters clinic near you.
