Head Lice
What are they?
Head lice are small, parasitic insects that infest hair on the head of people. Their six legs allow them to grasp and wander between hairs. They feed only on the blood of people, and feed once or more each day. They are more common on children than adults.
In general, a person infested with head lice will have fewer than a dozen live lice on his or her head at a time, although hundreds of developing, dead and hatched eggs may be present. A single insect is called a louse. A female louse can lay more than 100 eggs, called nits, in her lifetime. The female louse secretes a glue to attach each egg to a scalp hair, usually close to scalp level. They hatch about 8 days after they are laid, and grow to the adult stage about 9 to 12 days after hatching. Adult head lice survive just a few weeks on the scalp, but die within a day once removed from a person.
To continue reading this article, you must log in.
Subscribe to Harvard Health Online for immediate access to health news and information from Harvard Medical School.
- Research health conditions
- Check your symptoms
- Prepare for a doctor's visit or test
- Find the best treatments and procedures for you
- Explore options for better nutrition and exercise
I'd like to receive access to Harvard Health Online for only $4.99 a month.
Sign Me UpAlready a member? Login ».
Disclaimer:
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
