A head louse is a tan or greyish insect about the size of a strawberry seed. It feeds on human blood that it extracts from the scalp. The female louse produces a sticky substance that adheres each egg to a hair shaft. An egg is attached approximately 3/16 inch (4 millimeters) from the base of the shaft — an environment that provides an ideal temperature for incubating the egg.
The louse life cycle
A louse egg hatches after eight or nine days. What emerges is an immature form of the louse called a nymph. The nymph becomes a mature adult louse after nine to 12 days, and an adult lives for three to four weeks.
Head lice crawl, but they cannot jump or fly. Most often transmission of a head louse from one person to another is by direct contact. Therefore, transmission is most often within a family or among children who have close contact at school or play.
There's some evidence that brushing dry hair with static electricity may make a louse airborne for a short distance.
Indirect transmission is not likely, but lice may spread from one person to another by items such as:
- Hats and scarves
- Brushes and combs
- Hair accessories
Indirect transfer also could occur among items of clothing stored together. For example, hats or scarves hung on the same hook or stored in the same school locker could serve as vehicles for transmitting lice.
June 18, 2014
- American Academy of Pediatrics. Clinical report — Head lice. Pediatrics. 2010;126:392.
- Head lice: Frequently asked questions. Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/lice/head/gen_info/faqs.html. Accessed Jan. 29, 2014.
- Pickering LK, et al., eds. Red Book Online. 29th ed. Elk Grove Village, Ill.: American Academy of Pediatrics; 2012. http://aapredbook.aappublications.org. Accessed Jan. 29, 2014.
- Takano-Lee M, et al. Home remedies to control head lice: Assessment of home remedies to control the human head louse, Pediculus humanus capitis. Journal of Pediatric Nursing. 2004;19:393.
- Di Campli E, et al. Activity of tea tree oil and nerolidol alone or in combination against Pediculus capitis (head lice) and its eggs. Parasitology Research. 2012;111:1985.
- Gunning K, et al. Pediculosis and scabies: Treatment update. American Family Physician. 2012;86:535.
- Pollack RJ, et al. Overdiagnosis and consequent mismanagement of head louse infestations in North America. The Pediatric Infectious Disease Journal. 2000;19:689.
- Goldstein AO, et al. Pediculosis capitis. http://www.uptodate.com/home. Accessed Jan. 29, 2014.
- Head lice: Diagnosis. Centers for Disease Control and Prevention. http://www.cdc.gov/parasites/lice/head/diagnosis.html. Accessed Feb. 3, 2014.
- Anise. Natural Medicine Comprehensive Database. http://www.naturaldatabase.com. Accessed Jan. 29, 2014.
- Ylang ylang oil. Natural Medicine Comprehensive Database. http://www.naturaldatabase.com. Accessed Jan. 29, 2014.
- Mumcuoglu KY, et al. The in vivo pediculicidal efficacy of a natural remedy. The Israel Medical Association Journal. 2002;4:790.
- Hoecker, JL (expert opinion). Mayo Clinic, Rochester, Minn. Jan. 31, 2014.