You keep lice from coming back by finishing the full course of treatment, combing and rechecking for two to three weeks, and having everyone in the household checked at the same time. The CDC’s list of reasons lice treatment fails points the same way: misdiagnosis, not following the label, lice resisting the medicine, or reinfestation after a treatment that worked. Each of those has a fix, and none of them is scrubbing your house.
Why Lice Show Up Again About a Week Later
Eggs are one reason lice show up again about a week later. The CDC says nits take about a week to hatch, six to nine days, so eggs that survived the first application can hatch into a fresh crop of crawlers. It splits the medicines two ways: some kill lice and eggs, and retreatment is usually not required for those; others kill lice but not eggs, so a second treatment comes seven to nine days after the first, depending on the drug. Treat again after the eggs have hatched but before the new lice can lay their own.
A few lice moving slowly eight to twelve hours after treatment is not a reason to reapply, because it takes time to kill all the lice. If no dead lice turn up, or the lice look as active as before, the medicine may not be working. Talk to a healthcare provider before re-treating, and they may suggest a different medicine.
Keep Combing for Two to Three Weeks
Check and comb every two to three days for the next two to three weeks after treatment. The CDC and MedlinePlus both set that window, and the AAP’s comb-out method gives the mechanics: wet the hair, work a fine-tooth nit comb through one small section at a time, wipe the comb on a wet paper towel after each pass, and study the scalp, the comb and the towel. Part the hair down to the scalp in very small sections, in a brightly lit room.
Live eggs sit close to the skin, within about a quarter inch of the base of the hair shaft, and the CDC says nits attached farther out than that are almost always hatched or dead. A nit is easy to confuse with dandruff, dirt or a hair spray droplet; the tell is that a nit is firmly attached and the others are not. The AAP adds that the comb-out usually does not clear lice on its own, so it works alongside treatment, not instead of it.
Check Every Head in the House on the Same Day
Have everyone in the household checked on the same day, and treat the same day if live lice turn up. The CDC and the AAP both say household members and close contacts should be checked, and that everyone infested, plus anyone they share a bed with, should be treated at the same time. One skipped head can hand lice right back. Checking is not treating, though: lice medicine belongs on a head with living lice, and the AAP says to be certain before you start. A live nymph or adult louse is the clearest evidence, and because lice avoid light and move quickly, a magnifying lens and good lighting earn their keep. The CDC says misdiagnosis of head lice is common, so ask your healthcare provider if you are unsure. When the same child keeps getting lice, our post on why a child keeps getting lice works through the likely reasons.
What Needs Washing, and What Does Not
Keep the cleaning short: the CDC’s head lice guidance says spending much time and money on housecleaning is not necessary to avoid reinfestation, and that getting head lice is not related to cleanliness of you or your environment. Lice that fall off a person die within two days if they cannot feed. Wash what was worn or used in the two days before treatment, handle the combs and brushes, and keep the rest of the housework small.
| What it is | What the CDC and the AAP say to do |
|---|---|
| Clothing, towels and bed linens used in the two days before treatment | Machine wash and dry them on the hot water cycle, 130 degrees Fahrenheit, with high heat drying. |
| Items you cannot wash or dry clean | Seal them in a plastic bag and store them for two weeks. |
| Combs and brushes used by the person with lice | Soak them in hot water, at least 130 degrees Fahrenheit, for 5 to 10 minutes. |
| Fumigant sprays, fogs and household pesticides | Do not use them. They are not necessary and can be toxic if inhaled or absorbed through the skin. |
Habits That Head Off the Next Case
Lice crawl from one head to another, so the habits that matter keep heads apart. The CDC says the most common way to get head lice is head-to-head contact with a person who already has head lice, and that lice cannot hop or fly. Teach children to avoid hair-to-hair contact during play, sports, playground time, sleepovers and camp, and to keep hats, scarves, coats, sports uniforms, hair ribbons, barrettes, combs, brushes and towels to themselves. MedlinePlus adds headphones, hair ties and helmets. The AAP puts the chance of spread from items like those at very small, so contact is where your effort pays, and it says regular checks are a good way to spot head lice before they have time to multiply. That is the point of a steady nit-picking prevention routine.
Frequently Asked Questions
How long after treatment can lice come back?
The window to watch is the first two to three weeks, and live crawling lice at day seven to nine are the specific trigger for a second treatment. The AAP says an untreated infestation can repeat its cycle every three weeks, with newly hatched eggs reaching adulthood in about twelve to fourteen days.
Do I have to remove every nit?
Nits left in the hair are not proof that treatment failed. The CDC says nits may stay in hair after treatment, but successful treatment will kill crawling lice. Whether you need to remove them depends on the medicine: the CDC says you do not need to remove nits when treating with spinosad topical suspension, and otherwise to use nit combs to remove nits and lice from the hair shaft.
Can lice come back from the couch or from our pets?
Not from pets, since animals do not get or spread head lice. The CDC lists lying on a bed, couch, pillow, carpet or stuffed animal recently in contact with an infested person among the less common ways lice spread, and its advice is simply not to lie there. Picking up lice from a wig or hairpiece is extremely unlikely.
Does swimming spread lice?
Head lice are unlikely to spread in a swimming pool, and chlorine in pool water does not kill them either. The CDC says lice can survive under water for several hours. Shared towels, combs and brushes are the part of a pool day worth policing.
My child still itches. Are the lice back?
Itching by itself is not proof. The AAP says itching from head lice can last for weeks, even after the lice are gone, and the CDC describes the itch as an allergic reaction to louse bites. Look for a live louse before treating again.
Do mayonnaise or oils get rid of lice?
No. The CDC says there is no scientific evidence that suffocating head lice with mayonnaise, olive oil, margarine, butter or similar substances works, and the AAP says no studies prove petroleum jelly, tub margarine or essential oils work either. Never use gasoline or kerosene, or medicines made for animals.
How Lice Lifters of Mercer County Can Help
A second opinion saves a lot of guesswork when you are staring at a head full of specks. At Lice Lifters of Mercer County we check the whole family in one appointment, so no one in the house gets overlooked. Our professional lice treatment is non-toxic and done in one visit, and we keep same-day appointments open for families who found something this morning. The 30 Day Guarantee applies when the whole family is checked. If you cannot tell a live louse from an old nit or a fleck of dandruff, bring everyone in and let us look. You can book a head check and know where you stand today.
