What Do Clinical Studies Say About Head Lice Treatments?
Short answer: in randomized trials, permethrin cures 15% to 45% of children, spinosad about 85%, ivermectin lotion about 72%, abametapir about 81%, dimethicone about 70%, benzyl alcohol about 75%, and wet combing alone 57%. In the IRB-approved HALT study (commissioned by the formulation's developer; the publisher of this site is the licensee) of the Nit Happens pesticide-free kit (n=26), 89% of participants were lice free at day 15, and 95.8% when two participants judged to be re-infestations are excluded, with no adverse events. The numbers, the study designs and their limitations are summarized below.
A plain-language summary of the published research on how well head lice treatments work, and why some common treatments work less well than they used to. This page is educational and is not medical advice. Last reviewed: October 2026.
How to read lice treatment studies
Most head lice trials measure the share of people who are lice-free about 14 days after treatment. Checking at two weeks matters because eggs laid before treatment can hatch later. A few things to keep in mind:
- Vehicle-controlled trials compare a product to the same lotion without the active ingredient. They show how much the active ingredient adds.
- Head-to-head trials compare two real treatments, which is more useful when choosing between them.
- Combing changes results. Some trials let one group comb and not the other, which can make a product look better or worse than it is.
- Results vary by place and time, largely because lice resistance to some insecticides differs from region to region.
Resistance to permethrin and pyrethrins ("super lice")
Permethrin and pyrethrins are the active ingredients in many long-standing over-the-counter lice shampoos and rinses. Lice can carry genetic changes called knockdown resistance (kdr) mutations that make these insecticides much less effective.
A 2016 study in the Journal of Medical Entomology tested 14,281 lice from 138 sites in 48 U.S. states, collected between 2013 and 2015. The average frequency of kdr resistance mutations was 98.3%, and 42 of the 48 states had a frequency of 100%.
What this means: if a permethrin or pyrethrin product did not work, the lice may be resistant. That does not always mean it was used incorrectly. The American Academy of Pediatrics (AAP) 2022 clinical report advises considering local resistance patterns when choosing a treatment.
Summary of key trials
| Treatment | How it works | Key study | Main result (lice-free) |
|---|---|---|---|
| Spinosad 0.9% | Insecticide (acts on nerves) | Stough et al., Pediatrics, 2009 | 84.6% and 86.7% vs 44.9% and 42.9% with permethrin (day 14) |
| Ivermectin 0.5% lotion | Paralyzes lice | Pariser et al., NEJM, 2012 | 73.8% vs 17.6% with vehicle (day 15), one application |
| Oral ivermectin | Tablet taken by mouth | Chosidow et al., NEJM, 2010 | 95.2% vs 85.0% with malathion lotion (day 15), hard-to-treat cases |
| Dimethicone 4% | Physical: coats and immobilizes lice | Burgess et al., PLoS ONE, 2007 | 69.8% vs 33.3% with malathion |
| Benzyl alcohol 5% | Suffocates lice | Meinking et al., Pediatric Dermatology, 2010 | 76.2% and 75.0% vs 4.8% and 26.2% with vehicle (day 14) |
| Abametapir 0.74% | Blocks enzymes lice and eggs need | Bowles et al., Pediatric Dermatology, 2018 | Significantly more lice-free than vehicle after one application |
| Heated air (custom device) | Dehydrates lice and eggs | Goates et al., Pediatrics, 2006 | Killed 80% of hatched lice and 98% of eggs |
| Wet combing | Mechanical removal | Hill et al., BMJ, 2005 | 57% vs 13% with a single over-the-counter insecticide treatment |
| Nit Happens kit (pesticide-free gel plus comb) | Physical: gel kills lice and nits and loosens nit glue, then combed out | Villar and Rubio Rivera, HALT study, 2020 (commissioned by Arbor Development, developer and licensor of the formulation; Cartwheel, this site's publisher, is the licensee; IRB approved; not yet peer reviewed) | 89% at day 15 intent to treat, 95.8% per protocol; n=26, no comparison arm |
Study summaries by treatment
Spinosad 0.9% cream rinse
Two phase 3 trials (1,038 participants) compared spinosad with permethrin 1%. Fourteen days after the last treatment, 84.6% and 86.7% of spinosad users were lice-free, compared with 44.9% and 42.9% of permethrin users. The permethrin group also did nit combing and the spinosad group did not, yet spinosad still performed better. Spinosad is a prescription product in the U.S.
Ivermectin 0.5% lotion (topical)
Two vehicle-controlled trials (765 participants, age 6 months and older) tested a single 10-minute application with no nit combing. The share of people who were lice-free was:
- Day 2: 94.9% with ivermectin vs 31.3% with vehicle
- Day 8: 85.2% vs 20.8%
- Day 15: 73.8% vs 17.6%
Side effects were similar in both groups. Topical ivermectin lotion has been available over the counter in the U.S. since 2020.
Oral ivermectin
A cluster-randomized, double-blind trial enrolled 812 patients in 376 households in France, the U.K., Ireland and Israel. All had head lice that had not cleared after topical insecticide treatment. Two doses of oral ivermectin, one week apart, left 95.2% lice-free at day 15, compared with 85.0% for malathion 0.5% lotion. Oral ivermectin is not FDA-approved for head lice. This study only included patients who weighed at least 15 kg. It is a clinician's decision, usually for hard-to-treat cases.
Dimethicone 4% (a silicone-based lotion)
Dimethicone is not an insecticide. It coats lice and disrupts how they manage water, so resistance of the kdr type does not apply. In an assessor-blinded trial of 73 participants, 69.8% of those treated with dimethicone were cured, compared with 33.3% of those treated with malathion 0.5% (intention-to-treat). Only two participants had irritation, and both were in the malathion group. Across published dimethicone trials, cure rates after two applications one week apart range from roughly 69% to 92%.
Benzyl alcohol 5% lotion
Two phase 3, vehicle-controlled trials (250 participants) used two 10-minute applications one week apart. At day 14, 76.2% and 75.0% of the benzyl alcohol groups were lice-free, compared with 4.8% and 26.2% of the vehicle groups. Mild eye and skin irritation was uncommon.
Abametapir 0.74% lotion
Abametapir blocks enzymes that both lice and developing eggs need. In two phase 3 trials (704 participants, age 6 months and older), a single 10-minute application with no nit combing left significantly more people lice-free at day 14 than the vehicle lotion. It was approved by the FDA as a prescription treatment in 2020.
Heated air
A 2006 study of 169 children compared six ways of applying hot air. A custom device designed for lice treatment killed 80% of hatched lice and 98% of eggs, and nearly all children treated with it were lice-free at a one-week check. Regular consumer hair dryers were less effective in the study, so the results do not apply to using a home hair dryer.
Wet combing
The evidence on combing alone is mixed:
- In a 2005 U.K. trial of 133 children, four wet-combing sessions three days apart with conditioner left 57% lice-free, compared with 13% after a single over-the-counter insecticide treatment (malathion or permethrin).
- An earlier U.K. trial (Roberts et al., The Lancet, 2000) found the opposite: malathion outperformed combing (78% vs 38%).
Combing is safe and useful for checking whether treatment worked. How well it works alone depends heavily on how thoroughly and how often it is done.
Home remedies
Mayonnaise, olive oil, margarine and butter are often suggested for smothering lice. The CDC states that it does not have scientific evidence that these are an effective treatment.
Nit Happens kit (industry-commissioned study)
Disclosure: this study was commissioned by Arbor Development, developer and licensor of the formulation. Cartwheel Health, which publishes this site, is the licensee that makes and sells the product. It is included so readers can weigh it against the trials above, with its limits stated plainly.
The HALT study (Villar and Rubio Rivera, 2020) enrolled 26 participants ages 3 and older with active head lice at a community center in Homestead, Florida (visits on October 10 to 11, 17 and 24, 2020) and treated them with the kit then labeled H.A.L.T. Lice Treatment Kit, the formulation now sold as the Nit Happens Complete Lice Treatment Kit: a pesticide-free gel followed by combing with the included metal comb, applied up to twice about a week apart (12 participants needed the second application). At day 15, 89% were lice free on an intent-to-treat basis (everyone who started) and 95.8% when two participants judged to be re-infestations are excluded: both had been lice free on day 8, received no second treatment, and had lice again on day 15. After a single application, 54% were lice free at day 8. No adverse events were reported. The protocol was IRB approved (IntegReview, now part of Advarra).
What it does not show: the study had no comparison arm, so it cannot say how the kit performs against permethrin, dimethicone or wet combing head to head; it was small; and it has not yet been published in a peer-reviewed journal. A separate dermatologist-controlled 48-hour patch test on 27 adults (Evalulab, study 20H-0224-34) recorded zero reactions and classified the gel non-irritant. The study has its own page on this site, The H.A.L.T. Study, with the full design, every count, the dataset and the citation. Full details are also at gocartwheel.com/pages/clinical-evidence, and a three-page clinical summary (PDF) with the study design, exact counts and limitations is available for download, together with the investigators' final clinical report of December 3, 2020 (PDF, participant initials and photographs redacted) (both archived on Zenodo, DOI 10.5281/zenodo.23510395).
What the research means for families
- Treatment failure is common with older insecticide products, largely because of widespread resistance.
- Several newer options have strong trial results, including non-insecticide options such as dimethicone and benzyl alcohol, and newer active ingredients such as spinosad, ivermectin and abametapir.
- Follow the label. Many products need a second application about 7 to 10 days later to catch newly hatched lice.
- Check with a fine-toothed comb after treatment to confirm it worked.
- Talk to a pediatrician or pharmacist if lice persist after treatment, or for infants and anyone with a skin condition.
- Children do not need to miss school because of head lice, according to the AAP.
LiceTreatments.org is created by Cartwheel Health, makers of the Nit Happens lice treatment kit. This page summarizes independent, peer-reviewed research, with one exception: the Nit Happens study was commissioned by the formulation's developer and the product is sold by this site's publisher; it is labeled as such wherever it appears.
Sources
- Villar M, Rubio Rivera M. HALT study of the Nit Happens Complete Lice Treatment Kit. 2020. IRB approved (IntegReview). Commissioned by Arbor Development (Mike Hatten), developer and licensor of the formulation; Cartwheel Health is the licensee; not yet peer reviewed. Summary and methods; clinical summary PDF; final clinical report PDF (redacted), DOI 10.5281/zenodo.23510395
- Evalulab. Dermatologist-controlled 48-hour occlusive patch test of the Nit Happens treatment gel, study 20H-0224-34. 2020. n=27, zero reactions, classified non-irritant.
- Gellatly KJ, et al. Expansion of the knockdown resistance frequency map for human head lice in the United States using quantitative sequencing. J Med Entomol. 2016;53(3):653-659. Link
- Stough D, et al. Efficacy and safety of spinosad and permethrin creme rinses for pediculosis capitis (head lice). Pediatrics. 2009;124(3):e389-e395. Link
- Pariser DM, et al. Topical 0.5% ivermectin lotion for treatment of head lice. N Engl J Med. 2012;367(18):1687-1693. Link
- Chosidow O, et al. Oral ivermectin versus malathion lotion for difficult-to-treat head lice. N Engl J Med. 2010;362(10):896-905. Link
- Burgess IF, Lee PN, Matlock G. Randomised, controlled, assessor blind trial comparing 4% dimeticone lotion with 0.5% malathion liquid for head louse infestation. PLoS ONE. 2007;2(11):e1127. Link
- Meinking TL, et al. The clinical trials supporting benzyl alcohol lotion 5% (Ulesfia). Pediatr Dermatol. 2010;27(1):19-24. Link
- Bowles VM, et al. Clinical studies evaluating abametapir lotion, 0.74%, for the treatment of head louse infestation. Pediatr Dermatol. 2018. Link
- Goates BM, et al. An effective nonchemical treatment for head lice: a lot of hot air. Pediatrics. 2006;118(5):1962-1970. Link
- Hill N, Moor G, Cameron MM, et al. Single blind, randomised, comparative study of the Bug Buster kit and over the counter pediculicide treatments against head lice in the United Kingdom. BMJ. 2005;331(7513):384-387. Link
- Roberts RJ, et al. Comparison of wet combing with malathion for treatment of head lice in the UK: a pragmatic randomised controlled trial. Lancet. 2000;356(9229):540-544.
- American Academy of Pediatrics. Head Lice (clinical report). Pediatrics. 2022;150(4):e2022059282. Link
- Centers for Disease Control and Prevention. Treatment of Head Lice. Link