Head lice, scientifically known as Pediculus humanus capitis, are a common public health issue affecting millions. These tiny insects are frequent, particularly among school-aged children. Their presence is not an indicator of hygiene or socioeconomic status.
Understanding Head Lice Biology
Pediculus humanus capitis are small, wingless insects that live exclusively on the human scalp, feeding on human blood. Adult lice are typically gray or tan, about the size of a sesame seed, with six legs adapted for gripping hair shafts. Lice spend their entire lives on a human host, unable to survive more than one to two days off the scalp without a blood meal.
The life cycle of a head louse involves three distinct stages: egg, nymph, and adult. Eggs, commonly called nits, are oval-shaped, approximately 0.8 mm, and cemented firmly to the base of hair shafts near the scalp. Nits are typically yellowish-white, but can be white, tan, or brown, and take about 6 to 9 days to hatch.
Once hatched, a nit releases a nymph, an immature louse resembling a smaller version of the adult, roughly the size of a pinhead. Nymphs undergo three molts over about 7 days before maturing into adult lice. Adult female lice can lay up to 8 eggs daily, and their lifespan on a human head can extend up to 30 days.
Recognizing an Infestation
Identifying a head lice infestation often begins with intense scalp itching. This itching results from an allergic reaction to the saliva injected by the lice as they feed on blood. While itching is a primary sign, some individuals may not experience it immediately, with symptoms potentially taking 4 to 6 weeks to appear after initial infestation.
Visual inspection of hair and scalp is the most reliable way to confirm an infestation. Lice move quickly and avoid light, making them difficult to spot, but live lice may be seen crawling on the scalp or hair shafts. Inspection should focus on areas like the crown of the head, behind the ears, and the nape of the neck, where lice and nits are most commonly found.
Nits are often easier to see than live lice because they are firmly attached to the hair. They can be confused with dandruff, hair product residue, or dirt. A key distinction is that nits are cemented to the hair shaft and cannot be easily flicked or brushed away, unlike dandruff. Nits found more than about 6 millimeters from the scalp are typically dead or empty.
Effective Treatment Strategies
Treating a head lice infestation involves eliminating both live lice and their eggs. Over-the-counter (OTC) treatments are often the first line of defense, commonly containing insecticides like permethrin or pyrethrins. These products work by targeting the nervous system of the lice, and typically require a second application 7 to 10 days after the first to kill any newly hatched nymphs.
For cases where OTC treatments are ineffective or resistance is suspected, prescription medications are available. These include topical treatments like ivermectin lotion, malathion lotion, benzyl alcohol lotion, and spinosad topical suspension. Ivermectin lotion can kill most lice and newly hatched ones with a single use, often without requiring nit combing. Oral ivermectin is another prescription option, typically used when other treatments have not worked.
Physical removal through wet-combing is an important part of any treatment strategy. This technique involves thoroughly wetting the hair, applying a generous amount of conditioner to slow down the lice, and then systematically combing through small sections of hair from root to tip with a fine-toothed nit comb. After each stroke, the comb should be wiped clean to remove any lice or nits. This process should be repeated every few days for at least two to three weeks to ensure all newly hatched lice are removed before they can lay eggs.
Beyond treating the infested individual, certain household items require attention to prevent re-infestation. Clothing, bedding, and other items that have been in contact with the infested person’s head within the past two days should be machine-washed in hot water (at least 130°F or 54.4°C) and dried on high heat. Items that cannot be washed can be sealed in a plastic bag for two weeks, as lice cannot survive long off a human host. Combs and brushes should be soaked in hot water for 5 to 10 minutes.
Prevention and Common Misconceptions
Preventing the spread of head lice primarily involves avoiding direct head-to-head contact, the most common mode of transmission. This is particularly relevant in environments where close contact is frequent, such as schools, camps, or during playtime. Encouraging individuals not to share personal items that touch the head, including combs, brushes, hats, scarves, and hair accessories, can also help reduce transmission risk.
Regular scalp checks, especially for children, can aid in early detection and prompt treatment, minimizing wider spread. While it is not necessary to fumigate an entire home, vacuuming floors and furniture can help remove any lice or nits that may have fallen off.
Several common misconceptions surround head lice. One prevalent myth is that lice can jump or fly; however, these insects are wingless and only crawl from one head to another through direct contact. Another misunderstanding is that head lice prefer dirty hair, when in fact, they can infest any hair regardless of its cleanliness. Furthermore, head lice are human-specific parasites and cannot be transmitted to or from pets.