Head lice 101: What lice look like, how they behave, and how kids get them
Head lice are tiny parasites that live on the human head. They live and thrive by sucking tiny amounts of blood from the scalp and reproduce by laying their eggs in the hair. Perhaps surprisingly, head lice don't spread disease.
If your child has lice, or might have lice, print out our Lice Survival Guide Checklist for parents.
What do head lice (and their eggs) look like?
The adult head louse has six legs and is about the size of a sesame seed. Descriptions of their color vary, but generally they range from beige to gray and may become considerably darker when they feed.
Lice often appear to be the same color as the hair they've infested, making them hard to see with the naked eye. You can spot them most easily in the areas behind the ears and along the hairline on the back of the neck.
Female lice lay up to ten minuscule eggs a day. Lice eggs (called nits) are oval in shape. They may appear to be the color of their host's hair, ranging from white to yellow to brown.
What's the life cycle of a typical louse?
The female louse attaches her eggs to human hair shafts with a waterproof, glue-like substance. This ensures that the nits can't be washed, brushed, or blown away, unlike dandruff and other bits of stuff in the hair that often gets mistaken for nits.
She lays her eggs a fraction of an inch from the scalp, where it's nice and warm – just right for hatching. Nits typically hatch eight or nine days after they're laid. Once the eggs have hatched, their yellow or white shells remain attached to the hair shaft, moving farther from the scalp as the hair grows. As a result, empty nit shells attached to hairs are usually found farther away from the scalp than live eggs are.
Baby lice, known as nymphs, are not much bigger than the nits and tend to be light in color. Nine to 12 days later, they become adults and mate, the females lay their eggs, and the cycle continues.
An adult louse can live up to 30 days on the human head.
How did my child get lice?
Your child probably picked up lice from an infested sibling or playmate. Lice are crawling insects. They can't hop, jump, or fly, but they can crawl from one head to another when people put their heads together – for example, when they hug or lay their heads on the same pillow.
Once female lice find their way to a child's head, they lay eggs and begin to populate the area. You can't catch nits; they have to be laid by live lice.
Since lice can live for up to a day off of the human head, it's theoretically possible to get infested if your hair makes contact with items such as hats, combs, or brushes if they were used recently by an infested person. However, this is less likely than human-to-human spread.
A healthy louse will rarely leave a healthy head (except to crawl onto another healthy head!), and lice found on combs are usually injured or dead.
Are lice more common in dirty conditions?
It's a myth that lice are a product of poor hygiene or poverty. Head lice are equal-opportunity parasites. They like clean hair as well as dirty hair and can flourish in even the wealthiest communities.
So, when lice are going around, it's no one child or family's fault. If your child has lice, chances are they're traveling through the neighborhood or school. And your child has probably unknowingly infected others.
Head lice are most common among preschool- and elementary school-age children and their families and caregivers. Some studies suggest that girls get head lice more often than boys. This may be because they have more head-to-head contact with each other and longer hair that provides more warmth and darkness (two things lice love).
Interestingly, lice are much less common among African Americans in the United States than among people of other races. This may be because lice claws have a tougher time grasping the shape and width of African American hair.
Reviewed by pediatric dermatologist Anthony J. Mancini, M.D., head of the division of dermatology at Children's Memorial Hospital in Chicago.
Next: How to tell if your child has lice
Go back to the Head Lice Survival Guide for Parents
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Frankowski BL, et al. 2010. Clinical report: Head lice. Pediatrics 110(3):638.
National Pediculosis Association. Undated. http://www.headlice.org
New World Encyclopedia. Undated. Louse. http://www.newworldencyclopedia.org/entry/Louse
