Causes and Risk Factors of Head Lice

Head lice can cause a high level of anxiety. While there are many myths about how lice are spread, simple head-to-head contact is the usual culprit. Lice can spread via clothing, bedding, or other personal items, though this is not common. Head lice infestation affects millions of children and adults each year, in every socioeconomic condition. While undesirable, lice don't spread any diseases.

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Common Causes

The head louse is the parasitic insect Pediculus humanus capitis. Head lice like to live close to the scalp where they feed several times a day on blood. They can be found on the hair of the head, eyebrows, and eyelashes. They are especially likely to be found behind the ears and at the neckline.

While lice are a nuisance, they do not spread disease.

Life Cycle of Lice

Lice go through these phases:

  • Nits: Head lice eggs are called nits. They are oval, yellow to white in color, and about the size of a knot in a thread. They are laid close to the scalp, firmly attached to the hair shaft, and need body heat to incubate and hatch. They take six to nine days to do so.
  • Nymphs: The eggs hatch into nymphs, with the empty nit shell remaining attached to the hair shaft. The nymphs are about the size of the head of a pin and are yellow to rust in color. They develop into adults after about seven days.
  • Adult louse: The adult louse is about the size of a pinhead and looks like a moving grain of rice. It is oval with three legs on each side and is rust in color. It moves only by crawling, not by flying or hopping but move fast. Adult lice can live for up to 30 days on the head. They will quickly die if they leave the scalp, perhaps surviving up to a day or two at most, as they need to feed frequently.

Spread of Lice

Head-to-head (or hair-to-hair) contact is the easiest way for lice to spread. The biggest risk groups are children in preschool, daycare, and school, and their families.

While it's most common in young children, lice can spread to people of any age.

African Americans are less likely to have lice. It may be that the claws of the lice are adapted to grasp a hair shaft of a certain size and shape, which is less common among that demographic group. For others, lice can be found in hair of all lengths, short or long, and whether the hair is curly or straight.

While people often blame sharing hats, combs, brushes, helmets, and even headphones for spreading lice, contact with items that have touched an infested person is usually not problematic. Studies have shown there were no live lice on hats worn by kids with active lice infestations and no lice or nits on the floor of schools.

Researchers have not found an association between sharing combs, brushes, wall hooks, or lockers and getting lice. However, if someone in your family has lice, it's still a good idea to avoid sharing these items.

Parents typically blame other kids at school when their kids get lice, but some lice experts think that kids are more likely to get lice from family members at home or these other situations where head-to-head contact is likely:

  • Sleepovers and slumber parties
  • Sports activities
  • Overnight camps

Lifestyle Risk Factors

Lifestyle choices (other than those relating to head-to-head or hair-to-hair contact) don't generally influence your risk of head lice. Lice infestations are not related to hygiene, either personal (showering, washing hair) or environmental (the cleanliness of the home or school).

Lice infestations occur in families of all socioeconomic classes.

The following can contribute to the risk that it can be passed along to others.

  • Lack of screening: Lice continue to spread the longer a case goes undiagnosed and untreated. Screening by using a lice comb is a quick and efficient way to look for nits or live lice, as there may be no symptoms (itching or sores from scratching may be present, but not always). This is particularly advised if there's a known case of lice among close associates, like schoolmates.
  • Keeping quiet: Although school-wide head lice screening programs aren't usually effective, the news may prompt checks of students in the class, especially those most likely to have had direct head-to-head contact with the child that has head lice. Administrators are also likely to send a note to parents so they can perform checks at home; most take care not to include your/your child's name in the notification. If you are embarrassed, just say that you heard lice was going around and urge parents to check their kids.

If your child has lice, call your child's school nurse or program coordinator to report it.

Myths and Misinformation

Myths and misinformation can continue the cycle of spreading lice and getting an infestation again and again. Don't believe these common statements:

  • Special shampoos and conditioners can keep you from getting head lice.
  • They don't. There is no known preventative treatment.
  • Nits are always a sign that there is an active head lice infestation.
  • They aren't. Nits that are a half inch or more away from the scalp are non-viable and indicate an older infestation that may not be active.
  • No-nit policies help keep lice out of schools.
    They don't. The American Academy of Pediatrics recommends children return to school after their first treatment.
  • Home remedies can prevent and treat lice.
    There is no sufficient evidence that they do.
  • It is easy to manually remove live lice to treat an infestation.
    It can be done, but since the average infested person has at least 10 lice scurrying around, it certainly isn't easy.
  • You have to remove all of the nits.
  • You don't necessarily. The recommended re-treatment in nine days should kill hatching nits. But removing nits makes it easier to spot new nits and to know if the infestation is truly gone, so it may be worthwhile.
  • You have to disinfect your whole house.
    You only need to clean the things that the infested person's head likely had contact with, including clothing, sheets, hats, brushes, and pillowcases, etc. You should also vacuum carpeting, rugs, and furniture that the person sat or laid on within the last 48 hours.

Getting lice is a routine childhood and family problem. Panicking about them shouldn't be. Even if you or your child has a case that is hard to get rid of, your healthcare provider can help with treatment advice.

Head Lice Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Child

Frequently Asked Questions

  • Are lice caused by bacteria or viruses?

    No. Lice are minuscule parasitic insects. They're unrelated to any sort of microbial infection and do not spread disease. However, in very rare cases, scratching caused by extreme itching can lead to a secondary bacterial infection if the skin is broken.

  • What are some causes of itchy scalp besides lice?

    According to the American Academy of Dermatology, there are lots of reason your head and scalp might itch that do not involve lice:

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Head Lice. Prevention & Control

  2. Centers for Disease Control and Prevention. Head Lice. Biology

  3. Centers for Disease Control and Prevention. Head lice. Frequently asked questions (FAQs).

  4. Meister L, Ochsendorf F. Head Lice. Dtsch Arztebl Int. 2016;113(45):763-772. doi:10.3238/arztebl.2016.0763.

  5. American Academy of Pediatrics. Head Lice: What Parents Need to Know

  6. Centers for Disease Control and Prevention. Head Lice. Treatment

  7. American Academy of Dermatology. 10 reasons your scalp itches and how to get relief.

Additional Reading

By Vincent Iannelli, MD
 Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.