Most lice treatments take about two weeks from start to finish. That timeline accounts for two rounds of treatment spaced roughly nine days apart, plus combing sessions in between. A single application won’t do it because no treatment reliably kills every egg, so you need that second round to catch newly hatched lice before they can reproduce.
Why Treatment Takes Two Weeks
The two-week timeline is built around the lice life cycle. A female louse lays eggs (called nits) at the base of the hair shaft, and those eggs take about 8 to 9 days to hatch. Once hatched, the immature louse reaches adulthood in another 7 to 12 days. The goal of treatment is to kill all living lice with the first application, then apply a second treatment around day 9 to kill any nymphs that hatched from eggs the first round missed. Day 9 is considered optimal because it catches nymphs after they’ve emerged but before they’re old enough to lay new eggs.
If you skip the second treatment, even a few surviving eggs can restart the whole cycle.
What the First Few Days Look Like
After applying your first treatment, you can expect to see some lice still moving for up to 8 to 12 hours. That’s normal. The medication takes time to work. If you check the hair after that window and find dead lice, the product is doing its job. Use a fine-toothed nit comb to remove dead lice and any eggs you can see.
If lice are still moving at full speed 12 hours after treatment, the medication likely isn’t working. This is more common than you might expect. A global analysis of lice populations found that roughly 77% of head lice are resistant to the most widely used over-the-counter ingredients (pyrethroids like permethrin). In North America specifically, resistance rates have been measured above 97%. If your first treatment doesn’t seem effective, you’ll need a different product or a prescription option, which can add a few days to your overall timeline.
The Wet Combing Alternative
If you prefer to skip chemical treatments entirely, or if OTC products aren’t working, wet combing is a well-established method that relies on physically removing lice and eggs with a fine-toothed comb. You apply conditioner to wet hair, section it carefully, and comb through from root to tip, wiping the comb on a paper towel after each pass to check for lice.
Wet combing sessions need to happen every 3 to 4 days over a full two-week period. That typically works out to about four or five sessions total. It’s time-consuming, especially for long or thick hair, where a single session can take 30 minutes or more. But it works without any chemicals and gives you visual confirmation of progress each time.
Household Cleanup Doesn’t Take Long
The good news about cleaning your home is that lice are poor survivors away from a human head. Adult lice die within two days without a blood meal, and eggs that fall off the scalp usually die within a week because they need body heat to hatch. You don’t need to deep-clean your entire house.
Focus on items that touched the head in the previous 48 hours: pillowcases, hats, hair ties, and towels. Machine wash them in hot water or run them through the dryer on high heat for at least 20 minutes. Temperatures above 125°F for 10 minutes kill both lice and eggs. Items that can’t be washed, like stuffed animals, can go in a sealed plastic bag for two weeks or in the dryer on high for 20 minutes. Vacuum upholstered furniture and car seats, and you’re done. Fumigant sprays for the home are not recommended and aren’t necessary.
When Kids Can Return to School
Your child doesn’t need to miss much school. Both the American Academy of Pediatrics and the National Association of School Nurses recommend against “no-nit” policies, which used to require children to be completely free of eggs before returning to class. The current guidance is simpler: a child with lice can finish the school day, get treated that evening, and return to class the next morning.
The reasoning is straightforward. Nits are glued to hair shafts and don’t transfer between people. Many nits found during checks are already empty shells or too far from the scalp to be viable. Keeping kids home for days causes more harm than the lice themselves, which don’t carry disease and pose no health risk beyond itching.
Signs Treatment Isn’t Working
You should be seeing clear progress by the end of the two-week period. If you’re still finding live, active lice after completing both treatment rounds, a few things could be happening. The most common culprits, according to the CDC: the lice are resistant to the medication you used, conditioner or combination shampoo was applied before treatment (which can coat the hair and block the medication), or the treatment instructions weren’t followed exactly. Reinfestation from another person is also possible, especially if close contacts haven’t been checked.
The difference between treatment failure and reinfestation matters. If lice return within a day or two of treatment, resistance is the likely cause. If you’re lice-free for a week or two and then find them again, reinfestation from a classmate or family member is more probable. In either case, switching to a different treatment class or adding consistent wet combing usually resolves things within another two-week cycle.
Total Timeline at a Glance
- Day 1: First treatment application, followed by combing to remove dead lice and visible eggs.
- Days 2 to 8: Comb through hair every 3 to 4 days to remove any nymphs that hatch.
- Day 9: Second treatment application to kill newly hatched lice.
- Days 10 to 14: Continue combing every few days to confirm no live lice remain.
For most families, the active effort is concentrated in that first week, with the second treatment and follow-up combing wrapping things up by day 14. If resistance forces a switch to a different product, add another week or so to the timeline. Wet combing alone follows the same two-week schedule but requires more hands-on time at each session.