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Understanding Head Lice: What They Are and How They Spread

Head lice are small insects that live on the human scalp and feed on blood. These parasites are about the size of a sesame seed—roughly 2 to 3 millimeters long—and can be tan, gray, or brown in color. According to the Centers for Disease Control and Prevention (CDC), head lice affect millions of people annually in the United States, with an estimated 6 to 12 million infestations occurring each year, particularly among school-age children between ages 3 and 12.

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Understanding how lice spread is important for prevention and treatment. Head lice move from person to person through direct contact with an infested person's hair. This commonly happens when children play together, share items, or participate in sports. The insects do not jump or fly—they crawl. Contrary to popular belief, head lice are not a sign of poor hygiene or cleanliness. Anyone can get head lice regardless of their economic status, cleanliness habits, or hair type.

Head lice have a three-stage life cycle: nit (egg), nymph (young louse), and adult. Nits are oval-shaped eggs that are typically white or yellowish and firmly attached to hair shafts, usually near the scalp. Nymphs appear within 7 to 10 days and look like miniature adult lice. Adult lice can live 3 to 4 weeks on a human head and produce multiple eggs during their lifetime. A female louse can lay 4 to 8 eggs per day.

Other ways lice can spread include sharing personal items such as hats, hairbrushes, combs, hair clips, headphones, pillows, or blankets with an infested person. However, transmission through these objects is less common than direct head-to-head contact. Lice cannot survive more than 24 hours away from a human scalp, so environmental transmission is relatively rare. School environments are common places where head lice spread because children sit close together and may engage in physical play.

Practical Takeaway: Knowing that head lice spread through direct contact helps you understand prevention strategies. Monitor your child's scalp during school season, especially after activities involving close contact with other children. Encourage children to avoid sharing personal items like hats or headphones, and teach them about personal space during play activities.

Recognizing the Signs and Symptoms of Head Lice Infestation

Early detection of head lice makes treatment simpler and prevents spread to others. The most common sign of head lice is itching on the scalp, neck, or behind the ears. This itching occurs because lice bite the scalp to feed on blood, and some people have an allergic reaction to their saliva. However, not everyone itches—some people with head lice experience no itching at all, particularly during the first few weeks of infestation.

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Visual signs include nits and adult lice on the hair and scalp. Nits appear as small, oval bumps attached firmly to individual hair shafts. They are often found close to the scalp, particularly behind the ears and at the nape of the neck. Nits do not brush off easily like dandruff would. You may also see small red bumps or sores on the scalp, neck, or shoulders caused by scratching. In some cases, a secondary bacterial infection can develop from these scratches.

Adult lice are more difficult to spot because they move quickly and avoid light. They are about the size of a sesame seed and may appear tan, brown, or grayish. You are more likely to see nits than adult lice when inspecting the head. A person with head lice may also experience difficulty sleeping, irritability, or trouble concentrating at school, particularly if the infestation is severe.

To check for head lice, use a fine-toothed comb on wet hair under good lighting. Comb small sections of hair from scalp to tip. Wipe the comb onto a white paper towel to see if anything falls off. Nits and lice show up more easily against white paper. Check the entire scalp, including the top of the head, sides, back, and behind the ears. If you see even one nit or louse, infestation should be assumed. The presence of empty nit shells (which appear white or tan) indicates a previous infestation that may have been treated or resolved.

Practical Takeaway: Check your child's scalp regularly, especially during school months or after they complain of itching. If you find one nit, assume infestation and begin treatment. Use a fine-toothed comb and white paper for accurate detection, and check all family members living in the same household since lice often spread to multiple people.

Treatment Options: What Works and How They Work

Several treatment options are available for head lice, and they fall into two main categories: over-the-counter products and prescription medications. Over-the-counter treatments typically contain pyrethrins (a natural insecticide derived from chrysanthemum flowers) or permethrin (a synthetic version). Common over-the-counter products include Rid, Nix, and various store brands. These products come as shampoos, lotions, or creams and are usually applied to dry or damp hair, left on for a specific period (often 10 minutes), and then rinsed out.

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Prescription treatments have become more common in recent years because some head lice populations have developed resistance to traditional pyrethrins and permethrin. Prescription options include ivermectin (Stromectol), spinosad (Natroba), and benzyl alcohol (Ulesfia). Ivermectin is typically given as two doses taken by mouth one week apart. Spinosad and benzyl alcohol are applied topically like over-the-counter products. A healthcare provider can determine which treatment option may be appropriate based on the patient's age and medical history.

Regardless of the treatment product chosen, proper application is essential. Most treatments require a second application 7 to 10 days after the first application to kill newly hatched lice. It is important to follow package directions exactly regarding how long to leave the product on the hair, water temperature for rinsing, and timing of repeat applications. Even when directions are followed correctly, no treatment is 100 percent effective, which is why follow-up checks are necessary.

Wet combing is a non-chemical approach that some people use alongside or instead of medicated treatments. This method involves combing wet hair with a fine-toothed comb every 3 to 4 days for at least 2 weeks. While time-intensive, wet combing can be effective and has no chemical side effects. Some people combine this method with over-the-counter treatments for better results. After any treatment, continue checking the scalp for several weeks to ensure all lice and nits are gone.

Practical Takeaway: When treating head lice, choose a product appropriate for the person's age and follow all directions carefully. Mark the calendar for the second application seven to ten days later, as this follow-up dose is crucial. Check the head three days after treatment and continue checking weekly for two weeks. If lice persist after treatment, contact a healthcare provider about alternative options.

Beyond Medicated Treatment: Cleaning and Prevention Steps

Treating the infested person is only part of addressing head lice. Environmental cleaning and prevention measures help reduce the chance of reinfestation and spread to household members. Items that touched the infested person's head should be washed in hot water and dried on high heat. This includes bedding, pillows, stuffed animals that were slept with, and hats. Heat kills lice and nits effectively. Items should be washed in water that is at least 130 degrees Fahrenheit.

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Personal items like hairbrushes, combs, and hair clips should be soaked in hot water (at least 130 degrees Fahrenheit) for 5 to 10 minutes, or washed in a dishwasher on high heat. Items that cannot be washed, such as car seats or furniture, should be vacuumed thoroughly. Lice cannot survive on surfaces longer than 24 hours, so regular household cleaning is sufficient—expensive pest control treatments are not necessary.

Notify the school, daycare, or other places where the infested child spends time. This allows staff to