Head lice infestation

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For the biology of the animal, see Head louse.
Head lice infestation (pediculosis capitis)
Classification and external resources
Fig.4.Louse bites.jpg
Head lice bites on the nape of the neck
ICD-10 B85.0
DiseasesDB 9725
MedlinePlus 000840
eMedicine med/1769
MeSH D010373

Head lice infestation[1] (also known as pediculosis capitis, or as "having nits" or "having cooties")[1] the colonization of the hair by the head louse (Pediculus humanus capitis), typically only involves the head or scalp of the human host. Head lice feed on human blood; itching from lice bites is a common symptom of this condition.[2] Treatment includes application of topical insecticides such as a pyrethrin or permethrin, although a variety of herbal remedies are also common.[3]

Lice infestation in general is known as pediculosis, and occurs in many mammalian and bird species.[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)[citation needed]. Humans are hosts for two other lice as well — the body louse and the crab louse.

Head-lice 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. It has been suggested that in the past, head lice infection has been a mutualistic beneficial condition which helps to defend against the far more dangerous disease-carrying body louse.[5]

Signs and symptoms[edit]

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

The most common symptom of infestation is pruritus (itching) on the head which normally intensifies 3 to 4 weeks after the initial infestation[citation needed]. The bite reaction 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[citation needed]. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.


Head lice are generally spread through direct head-to-head contact with an infested person; transmission by sharing bedding or clothing such as headwear is much less common.[6] Body lice are spread through direct contact with the body, clothing or other personal items 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[citation needed]. Lice do not have wings and cannot jump[citation needed].

From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse[citation needed]. Full-grown lice are found to be the size of a sesame seed. Lice feed on blood 1–8 times each day by piercing the skin with their tiny needle-like mouthparts[citation needed]. Lice cannot burrow into the skin.

Head lice and body lice (Pediculus humanus) are similar in appearance, although the head louse is often smaller.[7] Pubic lice (Pthirus pubis), on the other hand, are quite distinctive. They have shorter bodies and pincer-like claws, and are colloquially known as "crabs"[citation needed]. Head lice are not known to be transmitters of diseases, unlike body lice.


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

The condition is diagnosed by the presence of lice or eggs in the hair, which is facilitated by using a magnifying glass or running a comb through the child's hair. In questionable cases, a child can be referred to a health professional. However, the condition is overdiagnosed, with extinct infestations being mistaken for active ones. As a result, lice-killing treatments are more often used on noninfested than infested children.[8] The use of a louse comb is the most effective way to detect living lice.[9] In cases of children with dirty, long and/or 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[citation needed]. 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[citation needed]. 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, 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.[9][10] 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).[11]


World War II-era American poster, created to prevent outbreaks of pediculosis among servicemen.

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 4–15 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.

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 2 weeks or by washing them at 60°C(140 degrees F) for 30 minutes.[12] This is because adult lice can survive only one to two days without a blood meal, and are highly dependent on human body warmth.[13] An insecticidal treatment of the house and furniture is not necessary.


Except for recent studies on neem seed extract,[14] 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,[15] and silicone-based lotions;[16] however all effective treatments require a two-fold process of killing both the adult lice and the eggs. Generally the eggs (nits) need to be manually picked off one by one in order to ensure all live eggs are removed.

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[citation needed].

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. Empty eggs of head lice may remain attached to the hair shaft long after the lice have been eliminated[citation needed], but rarely are adult lice seen even with an active infestation. Since there is no way to determine whether each egg is alive or dead, chemical treatment (which may not kill the eggs) should be considered only when live (crawling) lice are discovered in order to kill the adults. Instead, nitpicking, which is checking each hair strand for eggs and picking off each egg, should be used to prevent the possibility of an egg hatching resulting in reinfestation.

Tea tree oil is one of the few natural ingredients that have been proven to be effective in laboratory tests,[17] but The National Pediculosis Association recommends caution when using tea tree oil for the treatment of pregnant women and young children because of safety concerns.[18] Other home remedies such as putting vinegar, isopropyl alcohol, olive oil, mayonnaise, or melted butter under a shower cap have been disproven.[19] Similarly, the CDC claims that swimming has no effect on treating lice, and can in fact harm the treatment by commercial products.[20]


The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.[22]

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.[23] Lice infestation during that same period was more prevalent than chicken pox.[23]

About 6–12 million children between the ages of 3 and 11 are treated annually for head lice in the United States alone.[6] High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.[11][24]

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 socioeconomic status were found to be significant factors in head louse infestation[citation needed]. Girls are 2–4 times more frequently infested than boys[citation needed]. Children between 4 and 13 years of age are the most frequently infested group.[25] In the U.S., African-American children have lower rates of infestation.[6]

The United Kingdom's National Health Service[citation needed] 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.

Head lice (Pediculus humanus capitis) infestation is most frequent on children aged 3–10 and their families.[26] Females get head lice twice as often as males,[26] and infestation in persons of Afro-Caribbean or other black descent is rare because of hair consistency.[26] But these children may have nits that hatch and the live lice could be transferred by head contact to other children.[27]

See also[edit]


  1. ^ a b Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. ISBN 1-4160-2999-0. 
  2. ^ Burgess IF (1995). "Human lice and their management". Advances in Parasitology. Advances in Parasitology 36 (6): 271–342. doi:10.1016/S0065-308X(08)60493-5. ISBN 9780120317363. PMID 7484466.  |first2= missing |last2= in Authors list (help); |first3= missing |last3= in Authors list (help)
  3. ^ Burkhart CG, Burkhart CN, Burkhart KM; Burkhart; Burkhart (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. 
  4. ^ "Lice (Pediculosis)". The Merck Veterinary Manual. Whitehouse Station, NJ USA: Merck & Co. 2008. Retrieved 2008-10-08. 
  5. ^ Rozsa, Lajos; Apari P. (2012). "Why infest the loved ones – inherent human behaviour indicates former mutualism with head lice". Parasitology 139 (6): in press. doi:10.1017/S0031182012000017.  On-line full text available at link
  6. ^ a b c Division of Parasitic Diseases (DPD), National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED) (May 16, 2008). "Head lice fact sheet". Centers for Disease Control and Prevention website. Atlanta, GA: Department of Health and Human Services, US Government. Retrieved 28 May 2010. 
  7. ^ Bacot A (1917). "Contributions to the bionomics of Pediculus humanus (vestimenti) and Pediculus capitis". Parasitology 9 (2): 228–258. doi:10.1017/S0031182000006065. 
  8. ^ Pollack RJ, Kiszewski AE, Spielman A; Kiszewski; Spielman (2000). "Overdiagnosis and consequent mismanagement of head louse infestations in North America". The Pediatric Infectious Diseases Journal 19 (8): 689–93. doi:10.1097/00006454-200008000-00003. PMID 10959734. 
  9. ^ a b Mumcuoglu KY, Friger M, Ioffe-Uspensky I, Ben-Ishai F, Miller J; Friger; Ioffe-Uspensky; Ben-Ishai; Miller (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. 
  10. ^ Williams LK, Reichert A, MacKenzie WR, Hightower AW, Blake PA; Reichert; MacKenzie; Hightower; Blake (2001). "Lice, nits, and school policy". Pediatrics 107 (5): 1011–5. doi:10.1542/peds.107.5.1011. PMID 11331679. 
  11. ^ a b Mumcuoglu, Kosta Y.; Barker CS; Burgess IF; Combescot-Lang C; Dagleish RC; Larsen KS; Miller J; Roberts RJ; Taylan-Ozkan A. (2007). "International Guidelines for Effective Control of Head Louse Infestations". Journal of Drugs in Dermatology 6 (4): 409–14. PMID 17668538. 
  12. ^ Kidshealth.org – Head lice, page-3
  13. ^ University of Florida Dept of Entomology Circular 175
  14. ^ Abdel-Ghaffar, Fathy; Al-Quraishy, Saleh; Al-Rasheid, Khaled A. S.; Mehlhorn, Heinz (2012-01-01). "Efficacy of a single treatment of head lice with a neem seed extract: an in vivo and in vitro study on nits and motile stages". Parasitology Research (Springer Science+Business Media) 110 (1): 277–280. doi:10.1007/s00436-011-2484-3. PMID 21667206. Retrieved 2013-12-30. 
  15. ^ Goates BM, BM et al. (5 November 2006). "An Effective Nonchemical Treatment for Head Lice: A Lot of Hot Air". Pediatrics (American Academy of Pediatrics) 118 (5): 1962–1970. doi:10.1542/peds.2005-1847. PMID 17079567. Retrieved 2010-08-02. 
  16. ^ Ian F Burgess, Medical Entomology Centre, Insect Research & Development Limited (2009). "The mode of action of dimeticone 4% lotion against head lice, Pediculus capitis". BMC Pharmacol. 9: 3. doi:10.1186/1471-2210-9-3. PMC 2652450. PMID 19232080. 
  17. ^ Di Campli, Emanuela; Di Bartolomeo, Soraya; Delli Pizzi, Patricia; Di Giulio, Mara; Grande, Rossella; Nostro, Antonia; Cellini, Luigina (2012-11-01). "Activity of tea tree oil and nerolidol alone or in combination against Pediculus capitis (head lice) and its eggs". Parasitology Research (Springer Science+Business Media) 111 (1): 1985–1992. doi:10.1007/s00436-012-3045-0. Retrieved 2013-12-30.  Unknown parameter |DUPLICATE_date= ignored (help)
  18. ^ Eisenhower C, Farrington EA; Farrington (2012). "Advancements in the treatment of head lice in pediatrics". J Pediatr Health Care (Review) 26 (6): 451–61; quiz 462–4. doi:10.1016/j.pedhc.2012.05.004. PMID 23099312. 
  19. ^ Takano-Lee, M; Edman, J. D.; Mullens, B. A.; Clark, J. M. (December 2004). "Home Remedies to Control Head Lice: Assessment of Home Remedies to Control the Human Head Louse, Pediculus humanus capitis (Anoplura: Pediculidae)". Pediatric Nursing (journal) (Elsevier) 19 (6): 393–398. doi:10.1016/j.pedn.2004.11.002. PMID 15637580. Retrieved 2013-12-30. 
  20. ^ http://www.cdc.gov/healthywater/swimming/faq/#get_lice
  21. ^ Hootman J (April 2002). "Quality improvement projects related to pediculosis management". The Journal of school nursing : the official publication of the National Association of School Nurses 18 (2): 80–6. doi:10.1177/10598405020180020401. PMID 12017250. 
  22. ^ Norman G. Gratz (1998). "Human lice: Their prevalence, control and resistance to insecticides. A review 1985–1997" (PDF). Geneva, Switzerland: World Health Organization. Retrieved 2008-01-02. 
  23. ^ a b "A modern scourge: Parents scratch their heads over lice". Consumer Reports. February 1998. pp. 62–63. Retrieved 2008-10-10. 
  24. ^ Ian Burgess (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. 
  25. ^ 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. 
  26. ^ a b c Nutanson I. et al. (2008). "Pediculus humanus capitis: an update". Acta Dermatoven 17 (4): 147–59. 
  27. ^ James GH Dinulos (September 2008). "Lice (Pediculosis)". The Merck Manual. Merck & Co., Inc. Retrieved 2008-12-27. 

External links[edit]