Q: My daughter came home from camp with head lice. I treated her with Nix three days ago, but I found live lice again this morning. The package says to repeat the treatment in 7 to 10 days, but can I treat her now and then again in seven days? Should I switch to a different product? I’m not sure which one is best.
Finding live lice a few days after treatment can make you wonder whether the product worked, but I would not recommend treating again on day three. Nix contains permethrin, an insecticide that kills head lice and continues to have some activity on the hair after it is rinsed out. Nix product information recommends a second application if live lice are still present on day seven or later. Treating sooner or more frequently than recommended is unlikely to improve effectiveness and may increase scalp irritation.
Before deciding that Nix has failed, make sure the first treatment was used correctly. Hair should be washed with shampoo that does not contain conditioner, rinsed and towel dried. Enough Nix should be applied to completely saturate the hair and scalp, particularly behind the ears and at the back of the neck. Leave it on for 10 minutes before rinsing thoroughly. Using conditioner before treatment can interfere with permethrin remaining on the hair and may reduce its effectiveness.
Thorough combing is also an important part of managing head lice. After treatment, divide the hair into small sections and carefully work though each one with the fine-toothed lice comb, starting as close to the scalp as possible and combing through the ends. Pay particular attention behind the ears and at the back of the neck. Continue checking and combing the hair regularly over the following two weeks. A fine-toothed comb is more effective at finding live lice than simply looking through the hair.
You will probably also find nits, which are eggs laid by female lice and attached firmly to individual strands of hair. They can be difficult to remove because they are essentially glued to the hair and, unlike dandruff, do not simply brush or flake away. Use the fine-toothed comb to remove as many as possible, working in small sections. Stubborn nits can be grasped between your fingernails and slid down the strand of hair.
Finding nits does not necessarily mean treatment has failed. Empty eggshells can remain attached to the hair after the lice are gone, so finding a live, crawling louse is the best indication that an active infestation remains.
In your daughter's case, I would continue checking and combing her hair rather than applying another dose of Nix on day three. If live lice are still present on day seven, another Nix treatment can be applied. This second treatment helps kill lice that have hatched from eggs that survived the first treatment.
If live lice remain after two correctly applied Nix treatments, I recommend switching products. Resistance to permethrin has been reported in Canada, but treatment can also fail because the product was not applied correctly or the person became reinfested through close contact with someone who still has lice.
Several head lice products are available, and they do not all work the same way. Nix contains permethrin, an insecticide that affects the nervous system of the lice, while NYDA and Resultz are non-insecticide options. NYDA contains dimethicone, which works physically by entering and blocking the breathing system of the lice, essentially suffocating them. Resultz contains isopropyl myristate and cyclomethicone, which damage the protective outer coating of the lice, causing them to dehydrate and die. Because these products work differently from permethrin, they can be useful alternatives when treatment with Nix has failed. Each product has different age restrictions, application instructions and timing for the second treatment, so speak with your pharmacist before switching.
Itching can continue even after successful treatment because the scalp may remain irritated, so itching alone does not mean the lice are still present. Instead, look for live lice.
Other family members should also be checked, particularly anyone who has had close head-to-head contact with your daughter, but treatment should only be used when live lice are found. Head lice spread mainly through direct head-to-head contact and are not a sign of poor hygiene. There is also no need to disinfect your entire house. Focus on items that have recently been in close contact with the head, such as pillowcases, hats, hairbrushes and combs.