Facts About Head Lice
Fact Sheet on Head Lice
(Head lice, Body lice, Crabs, Cooties, Pediculosis)
What are lice?
Lice are wingless insects dating back to antiquity. They are host-adapted to humans and do not live on
household pets or in the general environment. Nits remain viable on clothing about 1 month. Body and
head lice can survive a week off the host without food, crab lice only two days. Nymphs survive 24 hours without food.
How are they acquired?
Lice do not fly or jump. Transmission is almost always through direct contact. Fomites and the
environment are extremely infrequent sources. As a rule of thumb, over 95% are transmitted through
person-to-person contact and less than 5% through indirect exposure.
How are they transmitted?
Lice are transmitted in community settings where close contact from play and living activities occur. For example, child care centers and nursing homes are settings conducive to transmission. While lice
infestations are recognized in elementary schools, it is safe to assume that only a minority of lice
infestations in school-age youngsters was actually acquired while at school. No exclusion from school or child care is necessary.
What are the risk factors for transmission?
Small children at play are the primary setting for transmission. Increasing risk would also be associated with home child-care; crowding, such as two families living in one dwelling or in a child-care center and any activity that brings youngsters together in informal settings such as sleep-overs, scouts, youth sports activities, etc. While schools are of lesser importance, best friends or playmates present risk from close associations at recess and during transportation such as in school buses.
What is the best approach to screening?
Screening requires a close visual examination of the individual’s head for crawling lice and nits (eggs). A small hand lens may help but is not essential. Very good lighting is desirable. Examine the hair and
scalp for at least 15 minutes to be reasonably sure the child does not have head lice. Most individuals
have fewer than 10 adult lice. The characteristic itching caused by lice may not develop for 30 days or
longer after infestation. A flashlight or ultraviolet light may help in detecting lice or eggs. Ideally parents should screen their own youngsters periodically, perhaps weekly, while they are in child-care or in the early grades at school. If lice are of high incidence in the community, parents should also screen all household members, children visiting the home, and frequent playmates.
What causes treatment failure?
Many strains of lice have developed resistance to the permethrin and lindane insecticides. Also, all
products have minimal ovicidal (nit killing) activity so nits remain viable, resulting in nymphal lice
emerging after treatment, thus a second treatment 7-10 days later is recommended.
What is the best approach to treatment?
The natural pyrethrins contained in over-the-counter products such as Rid, A-200 Pyrinate, Pronto, and
various store brands are perhaps the best class of insecticide because they are effective on lice and are minimally toxic to humans. Lindane is not recommended because of its toxic potential and demonstrated lice resistance. An important component of treatment is a daily shampoo for two weeks, (after the first use of medicated shampoo) with ordinary shampoo and cream rinse conditioner along with wet combing of the hair with a fine-tooth comb. This renders the hair slippery, impedes mobility of the lice, and water logs the individual louse to the point that it can be easily combed out. Lice and eggs should be removed from the comb between strokes on a paper towel or tissue paper. Medicated shampoo, such as those listed above, should be used on days 1 and 7. Over the two-week period, lice should become smaller and fewer in number, and then ultimately disappear.
How do you manage “worst case” situations?
It is challenging when several children in a household have a history of long-term infestation which may include involvement of the parent(s) or other adults. Compliance with treatment may be poor or
nonexistent. Intensive support from social worker services and local health departments may be
necessary. If the previously described therapy continues to fail, the healthcare professional may wish to consider “extra-label” use of oral ivermectin (Stromectol - Merck). Reference: “Drugs for Head Lice,”
The Medical Letter On Drugs and Therapeutics 38: 6-7, January 17, 1997.
How effective are home remedies?
Never use kerosene, gasoline, or other dangerous substances. Use of mayonnaise, vinegar, various
types of vegetable oils, Crisco, Vaseline, etc., may be of some benefit, but must be balanced against
difficulty in removing some products from the hair. (Note: Emphasize the regime of using the 2-week
shampoo, plus cream rinse conditioner, and fine tooth wet combing technique, with use of medicated
shampoos on days 1 and 7.)
How important is removal of nits?
Nits are problematic and represent the next generation of lice after treatment. Efforts to comb out nits
with plastic or metal combs are desirable but may test the patience of both parent and child. Some
schools have adopted “no-nit policies” that improve the success rate of individual treatment but provide
no assurance of eradicating the problem. The most important nits are proximal to the scalp. Any nit
more than 3/8 inch from the scalp is either hatched or no longer viable.
How important is the environment in lice transmission?
It has been overrated in the past to the point of mythical proportions. Laundering of linens and
vacuuming of upholstered furniture is more than adequate. Any environmental measures should not be
employed at the expense of efforts to do the two-week technique as outlined above. Environmental
spraying is worthless and should not be done. The pyrethrin sprays are not without risk and can
aggravate the health problems of children with asthma.
What can one do to prevent lice?
The best defense is frequent screening of youngsters at risk followed by diligent treatment, if necessary.
Assume there are lice in the community at all times of the year.