Several shampoos and topical treatments kill head lice, but the most effective option depends on whether the lice in your area have developed resistance to older pesticide-based products. Permethrin 1% lotion, the most widely available over-the-counter treatment, now faces a resistance rate of roughly 65% globally, and that number has climbed to 82% in studies conducted after 2015. That means the classic drugstore lice shampoo fails more often than it works for many families. Here’s what actually kills lice today and what to try if your first attempt doesn’t work.
Permethrin: The Standard OTC Option
Permethrin 1% lotion is the treatment most people reach for first. It’s available without a prescription, approved for children two months and older, and relatively gentle on the scalp. It works by attacking the nervous system of live lice. The problem is that lice have been exposed to this class of chemicals (pyrethroids) for decades, and a large meta-analysis of 20 studies found that 65% of head lice populations now carry genetic resistance to permethrin specifically. Before 2004, resistance sat around 33%. It has more than doubled since then.
If you use permethrin and still see live lice crawling 8 to 12 hours after treatment, resistance is the likely explanation. Permethrin also has limited ability to kill eggs, so even when it does work against live lice, you typically need a second application 7 to 9 days later to catch any newly hatched nymphs.
Dimethicone: A Physical Alternative
Dimethicone (sometimes spelled “dimeticone”) is a silicone-based product that kills lice through a completely different mechanism. Instead of acting as a pesticide, it coats the lice in a physical layer that disrupts their ability to manage water and blocks their airways. Because the action is purely physical, lice cannot develop genetic resistance to it the way they can to chemical treatments.
In one head-to-head trial, 4% dimethicone achieved a cure rate of about 77%, compared to just 34.5% for malathion, a prescription-strength pesticide. A separate study in Thailand found that 4% dimethicone liquid gel killed 100% of head lice within 15 minutes when used as directed, while other chemical shampoos tested alongside it killed between 0% and 60% even after 30 minutes of exposure. Dimethicone is not absorbed through the skin, which makes it a practical choice for families concerned about exposing children to pesticides.
The tradeoff is that dimethicone products vary in formulation and availability depending on your country. In the U.S., they’re sold under various brand names and are generally available without a prescription. Look for products listing dimethicone or dimeticone as the active ingredient, typically at a 4% concentration.
Prescription Treatments
When OTC options fail, a handful of prescription treatments offer stronger results. Two worth knowing about:
Ivermectin lotion (0.5%): Originally used in pill form to treat parasitic worm infections, ivermectin was approved by the FDA as a topical lotion for head lice in people six months and older. In clinical trials involving more than 780 people, most participants were lice-free after a single application without needing daily nit combing. The most common side effects were mild: eye irritation, dandruff, and dry skin. The single-application convenience is a significant advantage over treatments that require retreatment a week later.
Malathion lotion (0.5%): This is an older prescription option approved for children six years and older. It kills both live lice and some eggs. The major downside is that it’s flammable while wet on the hair. You cannot use a hair dryer, curling iron, flat iron, or be near any heat source during application. It can also irritate the scalp.
Benzyl alcohol lotion (5%): Approved for people six months and older, this suffocates live lice rather than poisoning them. It does not kill eggs, so a second treatment is necessary. It can cause skin irritation, and its safety in adults over 60 hasn’t been well studied.
Does Tea Tree Oil Work?
Tea tree oil is the most studied natural remedy for lice, and lab results are genuinely promising. At a 1% concentration, tea tree oil killed 100% of live lice within 30 minutes in controlled testing. It was less effective against eggs, though. A compound called nerolidol (found in some essential oils) showed better egg-killing ability, causing 50% of eggs to fail to hatch at 1% concentration after four days. When researchers combined tea tree oil and nerolidol in a 1:2 ratio, the mixture killed all live lice within 30 minutes and prevented eggs from hatching within five days.
The important caveat: these are lab results, not real-world clinical trials on people’s heads. Applying a precise concentration of essential oil evenly through hair in a bathroom is different from a controlled petri dish experiment. Tea tree oil can also irritate the scalp, especially at higher concentrations. It’s reasonable to try as a supplemental approach, but it shouldn’t be your only strategy if you’re dealing with an active infestation.
Why Retreatment Matters
Most lice shampoos kill live lice far more effectively than they kill eggs (called nits). Chemical pediculicides in particular often fail to kill all eggs. This is why a second treatment 7 to 9 days after the first is standard protocol for most products. That timing is deliberate: it targets nymphs that have hatched from surviving eggs but haven’t yet matured enough to lay new eggs themselves. If you skip the second treatment, you risk restarting the entire cycle.
The exceptions are ivermectin lotion, which often works with a single application, and dimethicone products, which physically coat eggs as well as live lice. Even with these, checking the hair carefully with a fine-toothed nit comb a week after treatment helps confirm the infestation is actually gone.
Age Restrictions to Know
Not every treatment is safe for every age group. Permethrin has the lowest age cutoff at two months. Benzyl alcohol and ivermectin lotion are approved starting at six months. Malathion jumps to six years. Lindane shampoo, an older prescription product, carries the most restrictions: it should not be used on children, elderly people, anyone with seizure disorders, pregnant or breastfeeding women, people with HIV, or anyone weighing less than 110 pounds. Misuse or accidental ingestion of lindane can be toxic to the brain and nervous system. It’s generally considered a last resort.
Choosing the Right Product
If you’re standing in a pharmacy aisle right now, permethrin 1% is still a reasonable first try because it’s cheap and widely available. But set realistic expectations: there’s a meaningful chance the lice in your area are resistant. If live lice are still moving 8 to 12 hours after treatment, switch to a different approach rather than reapplying the same product.
Dimethicone-based products are a strong second option, especially for families who want to avoid pesticides or suspect resistance. They’re available OTC in most places and sidestep the resistance problem entirely. For persistent cases that survive two rounds of OTC treatment, a prescription for ivermectin lotion is typically the most convenient and effective next step. Pair any treatment with thorough nit combing using a fine-toothed metal comb, and wash bedding and recently worn clothing in hot water to prevent reinfestation from stray lice.