Head Lice: Symptoms, Causes, & Treatment

By Zina Semenovskaya, MD
Medically reviewed checkmarkMedically reviewed
March 27, 2020

Lice are miniature parasitic insects that live on and impact the human body in a variety of ways. Though there are a variety of lice-related conditions that can affect people, including body lice, pubic lice, and sea lice, in this article I’ll focus on explaining one of the most common types: head lice.

Head lice are very common in children and can infest their person’s scalp, face, neck, and ears. They are highly contagious, moving between people by crawling from scalp to scalp during moments of close contact or hitching rides on shared belongings like brushes, hats, and combs. Once on a human head, they attach themselves to the scalp to feed on human blood, and lay their eggs at the base of hair shafts.

Though head lice are not considered dangerous and do not spread disease, they can be uncomfortable, and can lead to an itchy, irritated scalp. It is important to treat a head lice infestation right away to prevent spreading it to others, and to prevent the development of a secondary bacterial infection. If you suspect that you or a family member may be suffering from lice, this article will provide a comprehensive guide to the condition and explain how to get rid of lice for good.

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What Are Head Lice?

Head lice, medically referred to as pediculus humanus capitis, are wingless insects that infest human scalps, eyelashes and eyebrows, ears, and necks. They are found on humans around the globe, but in the United States, infestations primarily occur in school-aged children, due in large part to how closely children play during school and afterschool activities. In fact, the Centers for Disease Control and Prevention (CDC) estimates that up to 12 million American children under the age of 11 contract lice every year, enough infestations for many to consider lice a common childhood illness.

The head lice life cycle can be divided into three stages:

  • Nits: Adult female lice lay lice nits (eggs) at the base of a human hair shaft, no more than a fourth of an inch from a scalp. The nits are sticky, which keeps them firmly fixed to the hair shaft where they are deposited. They vary in color, but are oval shaped, and small enough to be commonly confused with hair spray, dandruff, or scabs. It takes 8-9 days for a nit to incubate, but even after a louse hatches, its empty shell or “casing” stays firmly affixed to the hair shaft. If you find a nit that is an inch or more from the scalp, it is either a nonviable egg or an empty shell casing.
  • Nymphs: Immature lice, or nymphs, must feed on human blood immediately upon hatching in order to survive. They look like adult lice, but smaller, with a gray, white, or tan color, and six legs. Nymphs mature into full adults 1-2 weeks after they hatch.
  • Adults: Mature lice are between 1-2 millimeters long, with six legs and hook-like claws to grasp human hair strands. They are usually gray, white, or tan but can be quite difficult to see unless an infestation is quite significant. They can live up to 30 days while feeding on a human scalp, but can only survive for 1-2 days without a blood meal. Female lice are generally larger than their male counterparts and, if they are able to mate, can lay up to six eggs a day.

A head lice infestation is never an indication of bad personal hygiene or poor living conditions. Head lice are found in both urban and rural areas—in schools, homes, libraries, and other public spaces—and are as likely to be found in wealthy neighborhoods as in poorer ones.You are just as likely to find lice in hair that is clean as you are to find them in hair that is dirty.

It’s important to note that head lice are a uniquely human nuisance. Because they are singularly suited to living on humans, lice cannot survive on, or be transmitted by, dogs, cats, or other household pets.

Symptoms of Head Lice

Children who have head lice report a “tickling” sensation on their scalp, or the feeling of something moving through their hair. They may complain about an itchy head, particularly around on the back of their neck or around their ears, but depending on their scalp sensitivity, they may not develop that symptom until they are already weeks into an infestation.

Children with lice may also display an unusually irritable mood, small red bumps on their scalp or neck, or infected, oozing sores on their head from scratching. Children with the condition often have difficulty sleeping, as head lice are most active at night.

If you see head lice on a child’s head, face, neck, sheets, hats, or brushes, that is the most obvious indicator that they are suffering from an infestation. You may also find nits but no adult lice, which may indicate that your child is in the early stages of the condition, or that they have leftover shell casings from a prior infestation.

Head lice vs. dandruff

Lice nits are sometimes mistaken for dandruff flakes because they can be a similar size and color. To distinguish between lice and dandruff, simply run a comb through your child’s hair. Dandruff flakes are easy to remove, while nits will stay stubbornly stuck where they are.

How Do You Get Head Lice?

You can get lice from contact with lice or their eggs. Head lice don’t have wings, but are capable of crawling from one scalp to another as people closely interact. Children may come into close contact with others and contract lice while they are at school, camp, daycare, sleepovers, or during sports activities or play.

Though it is less common, head lice can also be spread through personal contact with an infested item. Lice and their eggs can travel from one person to another by clinging to, or crawling on, someone’s personal belongings. Sharing clothing, headphones, combs, hats, hair ribbons, towels, bedsheets, pillows, or blankets with a person that has lice may lead to contracting lice yourself, as will laying on a shared couch or bed.

Household pets and other animals cannot contract human head lice, nor pass them to other humans.

Diagnosing Head Lice

In order to diagnose head lice, a doctor will take a close look at your child’s hair and scalp for visible signs of adult lice, nymphs, or nits. Because lice are sometimes hard to see, they may use a bright light, a magnifying glass, or a fine-tooth comb on your child’s head to increase visibility. Since viable nits glow in fluorescent light, doctors will sometimes use a black light to identify whether the nits they find are new, or are no longer viable, which perhaps trace back to an older infestation.

The doctor will only diagnose a head lice infestation if they can see live lice, or find hair shafts with nits located a fourth of an inch away from the scalp. If they do not see any lice, and only find nits more than a fourth of an inch away from the scalp, it is likely that a child had a previous infestation and no longer requires treatment.

Head Lice Treatment

Head lice are always treatable, though they can sometimes be tough to get rid of. Small infestations can sometimes go away on their own when there aren’t enough insects to maintain a population. However, most infestations will persist indefinitely without treatment.

If one person in the family has been diagnosed with a live head lice infestation, it’s important to get the rest of the household checked to make sure that everyone who needs treatment will receive it. All family members with infestations should be treated at the same time so they do not pass lice infestations back and forth.

You can treat head lice two ways:

  • Medicine: This includes over-the-counter (OTC) and prescription topical medications such as lice shampoo, cream rinses, and lotions.
  • Manual lice removal: You can also treat an infestation by hand using a lice comb, a fine-tooth comb designed specifically for identifying and removing lice and nits from individual hair shafts.

Before using any medication, be sure to check with a doctor to make sure that you’re following the correct course of treatment. If using lice medication, remove any clothing that could be stained or damaged, and apply it according to the instructions on the box or label. Be sure that you follow all safety instructions very carefully. Never let a child apply their own medication. Applying too much medication, or using medicine improperly, may be harmful for a child’s health (lice treatments vary in toxicity, and side effects from misuse can range from mild irritation to symptoms that are more severe).

On the other hand, using too little medication will not effectively kill lice or treat the infestation. Check with your doctor before applying a topical treatment a second or third time, or if your child experiences any swelling, irritation of the eyes, nose, or mouth, any symptoms indicating an allergic reaction, dizziness, or trouble breathing as a result of applying a lice treatment.

Combing for lice can be used in addition to, or instead of, medication to ensure that head lice are gone. Wet the hair, condition it, and then divide the hair into sections, using a nit comb to extract live lice and nits. Repeat every two to three days for approximately three weeks to ensure that the infestation has been completely removed.

Home remedies for lice, including the use of petroleum jelly, mayonnaise, tea tree oil, and olive oils are not considered a safe or scientifically effective way to treat infestations. Never use kerosene, gasoline, or other flammable liquids to treat a health condition.

After treating a person with head lice, it’s important to take supplemental household cleaning measures to ensure head lice won’t reinfest your child or spread to other family members.

  • Laundry: Wash any clothing, towels, bed linens, stuffed animals, pillows, or blankets exposed to a person with lice in hot water (at least 130° F) and dry them on high heat for at least 20 minutes. Dry clean items that cannot be washed, or seal them in a plastic bag for two weeks.
  • Hairbrushes: Soak all combs and brushes in hot water (at least 130 °F) for 5-10 minutes after use.
  • Furniture: Vacuum the floors, carpets, and any furniture that your child may have had direct contact with.

The chances of being infested by a louse that has fallen onto furniture or a carpet is very slim; head lice can only survive away from a human body for 1-2 days. If you are treating your child’s infestation properly, there is no need to take any extreme measures to treat your home. Never spray toxic fumigants or use other pesticides in your home, as they can be harmful to your family’s health.

If, after treating your child for head lice for two weeks, you can still see them, or if your child’s scalp looks inflamed or infected, call your doctor right away for further recommendations.

Preventing Head Lice

Because head lice infestations are both common and highly contagious, it can be difficult to prevent their spread entirely. If your child contracts head lice, it is not a poor reflection of their hygiene or your parenting abilities.

To help prevent your child from contracting head lice, talk to them about avoiding head-to-head contact during school and while at play. Instruct them not to share personal belongings like hats, scarves, brushes, combs, or hair ribbons with their classmates. Finally, continue to check their scalp, parting their hair with a fine-toothed comb, to catch and treat any new infestations as early as possible.

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K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Zina Semenovskaya, MD

Dr. Semenovskaya specializes in emergency medicine, and received her medical degree from Weill Cornell Medical College. She is currently the medical director at Remote Emergency Medicine Consulting, LLC and splits her time working clinically as an emergency medicine attending in California and Alaska. She is the first of our doctors to be fluent in Russian.