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definitions - Head_lice

head lice (n.)

1.infestation of the scalp with lice

Head Lice (n.)

1.(MeSH)Lice of the genus Pediculus, family Pediculidae. Pediculus humanus corporus is the human body louse and Pediculus humanus capitis is the human head louse.

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synonyms - Head_lice

Head Lice (n.) (MeSH)

Body Lice  (MeSH), Body Louse  (MeSH), Head Louse  (MeSH), Pediculi  (MeSH), Pediculus  (MeSH)

head lice (n.)

pediculosis capitis

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Head-louse infestation

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Head lice in humans
Classification and external resources

Head louse bites on the nape of the neck

Head-louse infestation or head lice (also referred to colloquially in British, Irish, Australian and New Zealand English as nits) is a human medical condition caused by the colonization of the hair and skin by the parasitic insect Pediculus humanus capitis—the head louse. Typically, only the head or scalp of the host is infested, although the disease can occur in other hairy parts of the body, like leg hairs. Head lice feed on human blood (hematophagy), and itching from louse bites is a common symptom of this condition.[1] Treatment typically includes application of topical insecticides such as a pyrethrin or permethrin, although a variety of folk remedies are also common.[2]

Lice infestation in general is known as pediculosis, and occurs in many mammalian and bird species.[3][4] The term pediculosis capitis, or simply "pediculosis", is sometimes used to refer to the specific human pediculosis due to P. humanus capitis (i.e., head-louse infestation). Humans are hosts for two other lice as well—the body louse and the crab louse.

Head-louse infestation is widely endemic, especially in children. It is a cause of some concern in public health, although, unlike human body lice, head lice are not carriers of other infectious diseases.



Adult male (left) and female (right) head lice

Head lice (Pediculus humanus capitis) infestation is most frequent on children aged 3–10 and their families. Females get head lice more often than males, and infestation in persons of Afro-Caribbean or other black descent is rare because of hair consistency. But, these children may have nits that hatch and the live louse could be transferred by head contact to other children.[5]

Head lice are spread through direct head-to-head contact with an infested person. Body lice are spread through direct contact with the body, clothing or other personal items or such,of a person already carrying lice. Pubic lice are most often spread by intimate contact with an infested person. Head lice occur on the head hair, body lice on the clothing, and pubic lice mainly on the hair near the groin. Human lice do not occur on pets or other animals. Lice do not have wings and cannot jump.

From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse. Full-grown lice are about the size of a sesame seed. Lice feed on blood once or more often each day by piercing the skin with their tiny needle-like mouthparts. Lice cannot burrow into the skin.

Head lice and body lice (Pediculus humanus) are similar in appearance, although the head louse is often smaller.[6] Pubic lice (Pthirus pubis), on the other hand, are quite distinctive. They have shorter bodies and pincer-like claws (hence, the nickname for pubic lice: "crabs").Pubic lice are commonly known as crab lice.


Lice comb (Bug Buster) wet combing with conditioner for diagnosis and treatment. Head lice can be seen in foam.

In order to diagnose infestation, the entire scalp should be combed thoroughly with a louse comb and the teeth of the comb should be examined for the presence of living lice after each time the comb passes through the hair. The use of a louse comb is the most effective way to detect living lice.[7] In cases of children with, dirty, and pretty long and curly/frizzy hair, an alternative method of diagnosis is examination by parting the hair at 2 cm intervals to look for moving lice near the scalp. With both methods, special attention should be paid to the area near the ears and the nape of the neck. The examiner should examine the scalp for at least 5 minutes. The use of a magnifying glass to examine the material collected between the teeth of the comb could prevent misdiagnosis.

The presence of nits alone however (Fig. 4), is not an accurate indicator of an active head louse infestation. Children with nits on their hair have a 35-40% chance of also being infested with living lice and eggs.[7][8] If lice are detected, the entire family needs to be checked (especially children up to the age of 13 years) with a louse comb and only those who are infested with living lice should be treated.As long as no living lice are detected, the child should be considered negative for head louse infestation. Accordingly, a child should be treated with a pediculicide ONLY when living lice are detected on his/her hair (not because he/she has louse eggs/nits on the hair and not because the scalp is itchy).[9]

Clinical symptoms

The most characteristic symptom of infestation is pruritus (itching) on the head which normally intensifies 3 to 4 weeks after the initial infestation. The bite reaction (Fig. 5) is very mild and it can be rarely seen between the hairs. Bites can be seen, especially in the neck of long-haired individuals when the hair is pushed aside. In rare cases, the itch scratch cycle can lead to secondary infection with impetigo and pyoderma. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.


The most common symptom of lice infestation is itching. Excessive scratching of the infested areas can cause sores, which may become infected.

Head lice may cause local infections, but are not a vector for epidemic microbial disease (see below). Head lice per se are a disease only if they cause symptoms. In the absence of discomfort or skin lesions, infestation is therefore only a condition and cosmetic problem for the carrier (not strictly a disease), though they may present a disease-transmission-risk for those others who will develop symptoms, if infected.


The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.[10] There is no product or method which assures 100% destruction of the eggs and hatched lice after a single treatment. However, there are a number of treatment modalities that can be employed with varying degrees of success. These methods include chemical treatments, natural products, combs, shaving, hot air, and silicone-based lotions.

Lice on the hair and body are usually treated with medicated shampoos or cream rinses. Nit combs can be used to remove lice and nits from the hair. Laundering clothes using high heat can eliminate body lice. Efforts to treat should focus on the hair or body (or clothes), and not on the home environment.

Some lice have become resistant to certain (but not all) insecticides used in commercially available anti-louse products. A physician or pharmacist can prescribe or suggest treatments. Because empty eggs of head lice may remain glued on the hair long after the lice have been eliminated, treatment should be considered only when live (crawling) lice are discovered.


Examination of the child’s head at regular intervals using a louse comb allows the diagnosis of louse infestation at an early stage. Early diagnosis makes treatment easier and reduces the possibility of infesting others. In times and areas when louse infestations are common, weekly examinations of children, especially those 4–13 yrs old, carried out by their parents will aid control. Additional examinations are necessary if the child came in contact with infested individuals, if the child frequently scratches his/her head, or if nits suddenly appear on the child’s hair. Keeping long hair tidy could be helpful in the prevention of infestations with head lice.In order to prevent new infestations, the hair of the child could be treated with 2–4 drops of concentrated rosemary oil every day, before he/she leaves for school or kindergarten. The oils can be combed through the hair using a regular comb or brush.[11] Clothes, towels, bedding, combs and brushes, which came in contact with the infested individual, can be disinfected either by leaving them outside for at least 3 days or by washing them at 60°C(140 degrees F) for 30 minutes. An insecticidal treatment of the house and furniture is not necessary.


Reliable data describing the usual incidence of infestation in the general public, in the average school community, or during specific times of the year are lacking.

—Janis Hootman, 2002[12]

Despite improvements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice.[13] Lice infestation during that same period was more prevalent than chicken pox.[13]

About 6-12 million people, mainly children, are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.[9][14]Normally head lice infest a new host only by close contact between individuals, making social contacts among children and parent child interactions more likely routes of infestation than shared combs, brushes, towels, clothing, beds or closets. Head-to-head contact is by far the most common route of lice transmission.The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e.g. school) and socio economic status were found to be significant factors in head louse infestation . Girls are 2-4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group.[15]

The United Kingdom's National Health Service, and many American health agencies[1][2][3], report that lice "prefer" clean hair, because it's easier to attach eggs and to cling to the strands, however, this is often contested.

Vectorial capacity

Head lice (Pediculus humanus capitis) are not known to be vectors of diseases, unlike body lice (Pediculus humanus humanus), which are known vectors of epidemic or louse-borne typhus (Rickettsia prowazeki), trench fever (Rochalimaea quintana) and louse-borne relapsing fever (Borrellia recurrentis).

Society and culture

School policy

Because head louse infestation occurs primarily in children,[12] much of the effort to prevent head lice transmission has focused on school and day care settings—places where large numbers of children come into close contact. Schools in the United States, Canada, and Australia commonly exclude infested students, and prevent return of those students until all lice, eggs, and nits are removed.[16] This is the basis of the "no-nit policy". Data from a primarily American study during 1998-1999 found that no-nit policies were present at 82% of the schools attended by children suspected of louse infestation.[17] A separate 1998 survey revealed that 60% of American school nurses felt that "forced absenteeism of any child who has any nits in their hair is a good idea."[18]
Head louse nits on human hair

School head lice policy involves a number of issues:

  • Establishing criteria to infer infestation
  • Screening asymptomatic children for evidence of infestation
  • Establishing the circumstances under which children will be inspected
  • Immediate exclusion of infested children
  • Establishing criteria to permit previously infested children to return to school (e.g., the no-nit policy)

All of these policies are controversial. In particular, a number of health researchers and organizations object to the required removal of nits (i.e., the no-nit policy).[16][19][20][21] Opponents to the no-nit policy point out that nits, being empty eggshells, have no clinical importance.[16] Transmission can only occur via live lice or eggs. Time-consuming nit removal, therefore, has no direct effect on transmission. This has led to the perception that the no-nit policy serves only to ease the workload of school nurses and punish the parents of infested children.[16]

Proponents of the no-nit policy counter that only a consistently nit-free child can be reliably shown to be infestation-free.[22] That is, the presence of nits serves as an indirect proxy for infestation status. Proponents argue that such a proxy is necessary because lice screening is prone false negative conclusions (i.e., failure to find lice present on actively infested children).[19][23] For example, a 1998 Israeli study found that 76% of live lice infestations were missed by visual inspection (as verified by subsequent combing methods).[7][12] Although lice cannot fly or jump, they are fast and agile in their native environment (i.e., clinging to hairs near the warmth of the scalp),[4][19] and will try to avoid the light used during inspection.[6][24] Lice colonies are also sparse (often fewer than 10 lice), which can contribute to difficulty in finding live specimens.[15] Further, lice populations consist predominantly of immature nymphs,[25] which are even smaller and harder to detect than adult lice.[7]

See also


  1. Burgess IF (1995). [Expression error: Missing operand for > "Human lice and their management"]. Advances in Parasitology 36: 271–342. doi:10.1016/S0065-308X(08)60493-5. PMID 7484466. 
  2. Burkhart CG, Burkhart CN, Burkhart KM (June 1998). "An assessment of topical and oral prescription and over-the-counter treatments for head lice". J. Am. Acad. Dermatol. 38 (6 Pt 1): 979–82. doi:10.1016/S0190-9622(98)70163-X. PMID 9632008. http://linkinghub.elsevier.com/retrieve/pii/S0190-9622(98)70163-X. 
  3. "Lice (Pediculosis)". The Merck Veterinary Manual. Whitehouse Station, NJ USA: Merck & Co.. 2008. http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/71900.htm&word=pediculosis. Retrieved 2008-10-08. 
  4. 4.0 4.1 Maunder, JW (1983). [Expression error: Missing operand for > "The Appreciation of Lice"]. Proceedings of the Royal Institution of Great Britain (London: Royal Institution of Great Britain) 55: 1–31. [unreliable source?]
  5. Dinulos, James GH (September 2008). "Lice (Pediculosis)". The Merck Manual. Merck & Co., Inc.. http://www.merck.com/mmpe/sec10/ch121/ch121e.html. Retrieved 2008-12-27. 
  6. 6.0 6.1 Bacot A (1917). [Expression error: Missing operand for > "Contributions to the bionomics of Pediculus humanus (vestimenti) and Pediculus capitis"]. Parasitology 9: 228–258. doi:10.1017/S0031182000006065. 
  7. 7.0 7.1 7.2 7.3 Mumcuoglu KY, Friger M, Ioffe-Uspensky I, Ben-Ishai F, Miller J (2001). "Louse comb versus direct visual examination for the diagnosis of head louse infestations". Pediatric dermatology 18 (1): 9–12. doi:10.1046/j.1525-1470.2001.018001009.x. PMID 11207962. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0736-8046&date=2001&volume=18&issue=1&spage=9. 
  8. Williams LK, Reichert A, MacKenzie WR, Hightower AW, Blake PA (2001). [Expression error: Missing operand for > "Lice, nits, and school policy"]. Pediatrics 107 (5): 1011–5. doi:10.1542/peds.107.5.1011. PMID 11331679. 
  9. 9.0 9.1 Mumcuoglu, Kosta Y.; Barker CS, Burgess IF, Combescot-Lang C, Dagleish RC, Larsen KS, Miller J, Roberts RJ, Taylan-Ozkan A. (2007). [Expression error: Missing operand for > "International Guidelines for Effective Control of Head Louse Infestations"]. Journal of Drugs in Dermatology 6 (4): 409–14. PMID 17668538. 
  10. Gratz, Norman G. (1998) (pdf). Human lice: Their prevalence, control and resistance to insecticides. A review 1985-1997. Geneva, Switzerland: World Health Organization. http://whqlibdoc.who.int/hq/1997/WHO_CTD_WHOPES_97.8.pdf. Retrieved 2008-01-02. 
  11. Mumcuoglu, Kosta Y.; R. Galun, U. Bach, J. Miller, and S. Magdassi (1996). [Expression error: Missing operand for > "Repellency of Essential Oils and Their Components to the Human Body Louse, Pediculus humanus humanus"]. Entomologia Experimentalis et Applicata (Wezep: The Netherlands Entomological Society) 78 (3): 309–314. 
  12. 12.0 12.1 12.2 Hootman J (April 2002). "Quality improvement projects related to pediculosis management" ([dead link]). The Journal of school nursing : the official publication of the National Association of School Nurses 18 (2): 80–6. PMID 12017250. http://jsn.sagepub.com/cgi/pmidlookup?view=long&pmid=12017250. 
  13. 13.0 13.1 "A modern scourge: Parents scratch their heads over lice". Consumer Reports. February 1998. pp. 62–63. http://web.ebscohost.com/ehost/pdf?vid=7&hid=102&sid=f97918a5-99c7-45da-a365-4324367c3566%40sessionmgr108. Retrieved 2008-10-10. 
  14. Burgess, Ian (2004). "Human Lice and their Control". Annual Review of Entomology (Annual Reviews) 49: 457–481. doi:10.1146/annurev.ento.49.061802.123253. PMID 14651472. http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.ento.49.061802.123253. 
  15. 15.0 15.1 Mumcuoglu KY, Miller J, Gofin R, et al. (September 1990). "Epidemiological studies on head lice infestation in Israel. I. Parasitological examination of children". International journal of dermatology 29 (7): 502–6. doi:10.1111/j.1365-4362.1990.tb04845.x. PMID 2228380. http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1365-4362.1990.tb04845.x. 
  16. 16.0 16.1 16.2 16.3 Mumcuoglu, Kosta Y.; Meinking, Terri A; Burkhart, Craig N; Burkhart, Craig G. (2006). "Head Louse Infestations: The "No Nit" Policy and Its Consequences". International Journal of Dermatology (International Society of Dermatology) 45 (8): 891–896. doi:10.1111/j.1365-4632.2006.02827.x. PMID 16911370. http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1365-4632.2006.02827.x. 
  17. Pollack RJ, Kiszewski AE, Spielman A (2000). [Expression error: Missing operand for > "Overdiagnosis and consequent mismanagement of head louse infestations in North America"]. Pediatr. Infect. Dis. J. 19 (8): 689–93. PMID 10959734. 
  18. Price JH, Burkhart CN, Burkhart CG, Islam R (April 1999). "School nurses' perceptions of and experiences with head lice". The Journal of school health 69 (4): 153–8. doi:10.1111/j.1746-1561.1999.tb04174.x. PMID 10354985. http://web.ebscohost.com/ehost/pdf?vid=2&hid=6&sid=1f619cd3-ab51-4f65-9f31-8aae5e14dc6b%40sessionmgr7. Retrieved 2008-10-10. 
  19. 19.0 19.1 19.2 Frankowski, Barbara L.; Leonard B. Weiner, the Committee on School Health, the Committee on Infectious Diseases (September 2002). "Head Lice: American Academy of Pediatrics Clinical Report". Pediatrics (American Academy of Pediatrics) 110 (3): 638–643. ISSN 0031-4005. PMID 12205271. http://aappolicy.aappublications.org/cgi/content/full/pediatrics;110/3/638. Retrieved 2008-10-10. 
  20. Frankowski, Barbara L. (September 2004). "American Academy of Pediatrics guidelines for the prevention and treatement of head lice infestation". The American Journal of Managed Care 10 (9): S269–S272. PMID 15515631. http://www.ajmc.com/article.cfm?ID=2704&CFID=14635274&CFTOKEN=65325173. Retrieved 2008-10-10. 
  21. National Association of School Nurses (July 2004). "Pediculosis in the School Community: Position Statement". Silver Spring, Maryland: National Association of School Nurses. http://www.nasn.org/Default.aspx?tabid=237. Retrieved 2008-10-10. 
  22. "The No Nit Policy: A Healthy Standard for Children and their Families". The National Pediculosis Association. 2008. http://www.headlice.org/downloads/nonitpolicy.htm. Retrieved 2008-10-12. 
  23. National Health and Medical Research Council (December 2005) (PDF). Staying Healthy in Child Care: Preventing infectious diseases in child care (4th ed.). Commonwealth of Australia. http://www.nhmrc.gov.au/publications/synopses/_files/ch43.pdf. 
  24. Nuttall, George H. F. (1919). [Expression error: Missing operand for > "The biology of Pediculus humanus, Supplementary notes"]. Parasitology 11 (2): 201–221. 
  25. Buxton, Patrick A. (1947). "The biology of Pediculus humanus". The Louse; an account of the lice which infest man, their medical importance and control (2nd ed.). London: Edward Arnold. pp. 24–72. 


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