Head lice are tiny parasites that live on the human scalp, a common issue, particularly among school-aged children. These parasites feed on blood from the scalp and can cause itching and irritation. Medicated shampoos are a widely used initial treatment for addressing these infestations.
Understanding Medicated Shampoos
Medicated shampoos typically contain active ingredients that target the nervous system of the parasites or work by suffocating them. Common over-the-counter (OTC) options include pyrethrins, derived from chrysanthemum flowers, and permethrin, a synthetic version. These compounds are pediculicides, formulated to paralyze and kill lice.
Other active ingredients include malathion, ivermectin, and spinosad. Malathion is an organophosphate that kills lice and some eggs. Ivermectin and spinosad are newer options that can kill both lice and unhatched eggs, potentially reducing the need for repeat treatments. Dimethicone-based treatments work differently by suffocating lice rather than poisoning them, which can be effective against resistant strains.
Effectiveness and Proper Use
Medicated shampoos are generally effective at killing live lice. However, many formulations, especially older over-the-counter types, do not consistently kill all lice eggs (nits). This means unhatched eggs can remain and later hatch into new lice, leading to continued infestation.
Successful treatment relies on precise application of the shampoo. It is important to thoroughly saturate the hair and scalp, ensuring coverage, particularly behind the ears and at the nape of the neck. The product needs to remain on the hair for the recommended time, typically around 10 minutes, before rinsing. An important step is a second application, 7 to 9 days after the first, to kill any newly hatched lice that survived the initial treatment.
After shampooing, thorough nit combing with a fine-toothed comb is important to remove dead lice and any remaining nits. This physical removal helps ensure complete eradication and is an important part of the treatment process. Some products may include a comb for this purpose.
When Treatment Isn’t Enough
Sometimes, medicated shampoo treatments may not fully resolve a lice infestation. One reason for this is the increasing resistance of lice to certain active ingredients, a phenomenon sometimes referred to as “super lice.” Lice, like other insects, can develop genetic mutations that make them resistant to common chemicals like pyrethrins and permethrin. In some regions, a significant percentage of lice populations have developed this resistance.
Other common reasons for treatment failure include improper application, such as not leaving the shampoo on long enough or missing areas of the scalp. Re-infestation can also occur if untreated household members are present or if individuals come into contact with lice again shortly after treatment. If over-the-counter treatments are not effective, or if symptoms persist, it may be necessary to consult a healthcare provider. They can recommend alternative prescription medications with different active ingredients, such as those containing benzyl alcohol, ivermectin, or spinosad, or suggest professional lice removal services.
Preventing Re-infestation
Preventing future lice infestations involves practical steps aimed at minimizing transmission. Head-to-head contact is the primary way lice spread, so encouraging children to avoid this during play or group activities is important. Lice cannot jump or fly; they crawl from one head to another.
Sharing personal items like combs, brushes, hats, scarves, and headphones should be avoided. While lice do not survive long off a human host (typically less than two days), cleaning these items can help prevent re-infestation. Regularly checking family members for lice and nits, especially after potential exposure, can aid in early detection and treatment. For household items that may have come into contact with lice, machine washing bedding, clothing, and towels in hot water (at least 130°F) and drying on high heat is recommended. Items that cannot be washed can be sealed in a plastic bag for two weeks.