Head lice are killed by specific chemical treatments, prescription medications, heated air devices, and physical removal with a fine-toothed comb. The catch is that the most common over-the-counter options don’t work nearly as well as they used to. A large meta-analysis found that after 2015, roughly 82% of head lice carried genetic resistance to the active ingredients in the most popular drugstore products. That means your first attempt may fail, and knowing which treatments actually work saves you days of frustration.
Why Drugstore Treatments Often Fail
The two most widely available over-the-counter lice treatments contain permethrin or pyrethrins. These have been the go-to options for decades, which is exactly the problem. Lice have evolved resistance at a striking pace. A study tracking North American lice over ten years found pyrethroid resistance climbed from 84% in the early 2000s to over 99% by the late 2000s. A separate U.S. study found 98.3% of lice sampled carried the gene for pyrethroid resistance.
This doesn’t mean these products never work. In areas where resistance hasn’t fully taken hold, they can still clear an infestation. But if you’ve applied a permethrin-based product correctly, followed the instructions, and still see live lice crawling two days later, resistance is the most likely explanation. Repeating the same product won’t fix it.
Prescription Treatments That Work Differently
When over-the-counter products fail, prescription options use entirely different mechanisms that resistant lice can’t dodge. Three are worth knowing about.
Spinosad 0.9% topical suspension is derived from soil bacteria and kills both live lice and unhatched eggs. Because it handles eggs too, retreatment is usually unnecessary, and you don’t even need to comb out nits afterward. It’s approved for children six months and older. You only repeat it if you see live lice crawling seven days later.
Ivermectin lotion 0.5% kills live lice and, while it doesn’t destroy eggs directly, prevents newly hatched lice from surviving. A single application on dry hair is effective for most people, with no nit combing required. It’s also approved from six months of age.
Malathion lotion 0.5% kills live lice and some eggs. It’s approved for ages six and up. A second treatment is recommended if live lice remain 7 to 9 days later. One important safety note: malathion is flammable. You cannot use hair dryers, curling irons, flat irons, or any electrical heat source while the product is on your hair or while hair is still wet from the application.
Heated Air Devices
Professional heated air treatment offers a completely non-chemical option. A clinical study tested a custom device that blows controlled hot air through the hair for 30 minutes. It killed nearly 100% of eggs and 80% of hatched lice in a single session. When researchers checked subjects one week later, virtually all were cured. The appeal here is simple: lice can’t develop resistance to heat the way they can to chemicals. These treatments are available at specialized lice clinics, not at home, and typically cost more than a drugstore product.
Wet Combing as a Standalone Method
A fine-toothed nit comb physically removes lice and eggs from the hair shaft. Flea combs designed for cats and dogs also work. Wet combing is the only method with zero resistance concerns and no chemical exposure, making it the safest option for very young children or anyone who prefers to avoid medications entirely.
The tradeoff is time and persistence. After any treatment, the CDC recommends checking hair and combing out lice and nits every 2 to 3 days for 2 to 3 weeks. If you’re using wet combing as your only method, that schedule is non-negotiable. Skipping sessions lets newly hatched lice mature and lay more eggs, restarting the cycle. Combing works best on wet, conditioned hair, which slows lice down and makes them easier to catch on the comb’s teeth.
Home Remedies: What the Evidence Shows
Mayonnaise, olive oil, vinegar, and coconut oil are widely recommended online. The idea is that coating lice in a thick substance suffocates them. Researchers tested this directly, and the results were disappointing. Most home remedy products caused little louse mortality and did almost nothing to prevent egg hatching. It was also extremely difficult to drown lice even after 8 hours of water submersion, suggesting that suffocation is a far less reliable mechanism than people assume.
Petroleum jelly was the one partial exception. It caused significant louse mortality and allowed only 6% of eggs to hatch. But it’s notoriously difficult to wash out of hair, often requiring multiple shampoos with dish soap or similar degreasers. The researchers concluded that none of the home remedies surveyed was an effective means of louse control, and that time spent on them would be better directed toward proven chemical treatments or thorough manual combing.
The Retreatment Window
Most lice treatments that kill adult lice don’t kill all the eggs. Lice eggs (nits) hatch in roughly 7 to 10 days, which is why retreatment timing matters so much. The second application targets newly hatched nymphs before they’re old enough to lay eggs themselves. If you treat on day one and retreat on day 9, you catch nymphs that hatched after the first round but haven’t yet reproduced. Miss that window and the cycle continues.
Spinosad is the notable exception: because it kills eggs too, a single application is usually enough. For every other treatment, assume you’ll need that second round unless you’re seeing zero live lice at the 7-day check.
Cleaning Your Home
Head lice die within two days of falling off a human host. They can’t feed on anything else, so your couch and carpet aren’t breeding grounds. Nits that fall off the head usually die within a week because they need the warmth of the scalp to survive.
Still, a basic cleaning routine eliminates stragglers. Wash bedding, pillowcases, and any recently worn hats or scarves in hot water of at least 130°F, then run them through the dryer on high heat. Items that can’t be washed (stuffed animals, decorative pillows) can be sealed in a plastic bag for two weeks. Vacuuming furniture and car seats is reasonable, but fumigant sprays for furniture are unnecessary and not recommended by the CDC.
Age Limits for Common Treatments
For children under six months, manual removal with a nit comb is the only recommended option. Spinosad and ivermectin lotion are both approved starting at six months. Malathion is approved for children six years and older. Over-the-counter permethrin products are generally labeled for ages two months and up, though their effectiveness is limited by resistance. If your child is under two, checking with a pediatrician before applying any chemical product is a practical step, since the youngest children have the most sensitive skin and the fewest approved options.