Head lice are tiny parasitic insects that live on the human scalp and feed on blood. Infestations are common, especially among school-age children, and require targeted treatment to interrupt the louse life cycle. Effective eradication depends on selecting the right topical solution and using precise application methods to kill both adult lice and the eggs, called nits.
Over-the-Counter Treatment Options
Over-the-counter (OTC) treatments for head lice fall into two main categories: neurotoxic insecticides and physical mechanisms. Products containing pyrethrins (derived from the chrysanthemum flower) and permethrin (a synthetic version) are widely available. Both act as neurotoxins by disrupting the nerve cell membranes of the louse, leading to paralysis and death.
These neurotoxic agents are effective at killing live adult lice, but their ovicidal activity, or ability to kill the nits, can be inconsistent. Because of this limitation, a second application is nearly always necessary to kill any nymphs that hatch after the initial treatment. Furthermore, their effectiveness has declined in many regions due to the development of resistance in louse populations.
Non-pesticide alternatives use occlusive agents, such as dimethicone, a silicone-based oil. This substance kills lice through a physical mechanism, such as coating the louse and blocking its respiratory system. This physical mode of action makes it highly unlikely for lice to develop genetic resistance, offering an advantage over chemical treatments. Dimethicone treatments are highly effective, often showing success rates over 70% after two applications.
Recognizing and Handling Resistant Lice
The growing prevalence of treatment failure is often due to “super lice.” This term describes head lice that have developed genetic mutations in their nervous system, allowing them to survive the effects of pyrethrins and permethrin. This resistance has reduced the effectiveness of traditional OTC treatments.
Treatment failure should be suspected if live, crawling lice are still observed in the hair 8 to 12 hours after a thorough and correct application of an insecticide product. If the product is not working, do not simply reapply the same chemical repeatedly, as this exposes the person to unnecessary chemicals and will likely not resolve the infestation. Instead, switching to a product with a different mechanism of action, such as a dimethicone-based solution, is recommended.
If multiple OTC treatments have failed, consult a healthcare provider for prescription-strength options. Treatments containing ivermectin or spinosad use different active ingredients that are not affected by common pyrethroid resistance mutations. These are typically reserved for cases where over-the-counter treatments have proven unsuccessful.
Step-by-Step Guide to Successful Eradication
Successful eradication requires meticulous attention to the application process, regardless of the product chosen. Before applying any topical treatment, remove any clothing that could become wet or stained. The product must be applied fully, ensuring the entire scalp and all hair strands are saturated, paying close attention to the areas behind the ears and the nape of the neck where lice commonly congregate.
Follow the manufacturer’s directions regarding whether the hair should be dry or damp and the precise time the product must remain on the head. Rinsing the product off too soon is a common cause of treatment failure, preventing the active ingredients from fully killing the lice. After the required time, the hair should be thoroughly rinsed.
Mechanical removal is a mandatory step for ensuring complete success, particularly because many treatments do not kill 100% of the nits. Using a fine-toothed nit comb, comb the hair from the scalp to the end of the hair, wiping the comb on a paper towel after each pass to inspect for and remove any lice or eggs. This process should be repeated every two to three days for several weeks to catch any newly hatched nymphs.
The second application is a crucial element of the treatment protocol and should be performed seven to ten days after the first one. This timing is based on the louse life cycle, aiming to kill any nymphs that have hatched from surviving nits before they mature and lay new eggs. Treating only once often allows the infestation to restart.
Beyond treating the hair, limited environmental cleanup helps to reduce the small risk of re-infestation.
- Machine wash and dry all bedding, clothing, and towels used by the infested person in the two days prior to treatment, using hot water (at least 130°F) and a high heat drying cycle.
- Items that cannot be washed, such as stuffed animals, can be sealed in a plastic bag for two weeks, as lice cannot survive long off a human host.