PEST NOTES Publication 7446

University of California

Agriculture and Natural Resources Revised August 2001

HEAD LICEIntegrated Pest Management in and around the Home

Many families with young childrenhave at least one encounter with thehead louse, Pediculus humanus capitis.Head lice can infest people of all ages,but children are prone to infestationsbecause of their habit of playing inclose contact, sharing hats, head-phones, combs and brushes, sleepingbags, stuffed animals, and clothing. Infact, the problem of head lice can be sorampant among preschool and school-aged children that often schools mustwork in conjunction with many fami-lies to control an infestation. An indi-vidual family may be able to controlhead lice at home, but the child can bereinfested when he/she comes in con-tact with an untreated, infested child.

WHAT TO LOOK FORThe most common symptom of infesta-tion is intense itching on the back of

the head or neck. The itching occurswhen the lice bite and suck blood fromthe scalp. Immediately examine chil-dren who repeatedly scratch theirheads. Because lice can be hard to spot,examine individual hair shafts, espe-cially at the nape of the neck and be-hind the ears. With a good light source,look for tiny, white eggs (nits) glued tothe hair near the scalp (Fig. 1) and forsmall, quickly crawling, flat insects.Hatched and unhatched eggs can bedifferentiated with the aid of a magni-fying lens: developing eggs are some-what dark in color but after hatchingthe egg cases are white. Nits hatchabout 7 to 11 days after being laid, soeggs further than 1⁄4 inch away fromthe scalp have probably alreadyhatched. An empty egg case can bedistinguished from a flake of dandruffbecause it sticks to the hair, while otherparticles can be flicked or washed off.

LIFE CYCLEHead lice spend their entire life on thehairy part of the head. The six-legged,wingless adult head louse is about thesize of a sesame seed and ranges incolor from tan to gray. Each of its sixlegs ends in a claw that is used tograsp the hair shaft. While head licecan crawl relatively quickly, they can-not hop, fly, or jump. Therefore, directcontact with an infested object or per-son is required to become infested.Because head lice live and breed com-pletely in human hair, they only sur-vive for about 1 to 2 days if they dropoff a person. They cannot live on familypets.

The eggs of the louse are laid on thehead hairs, usually at the junction of

the scalp and hair shaft. The egg iscoated with a gluelike substance thatcements it to the hair. Most eggs arelaid at night. Each female producesabout three to five eggs in a 24-hourperiod and lives for about 7 to 10 days.Most of the eggs hatch within 7 to 11days. To survive, a newly hatched lousemust have a blood meal within minutesof birth. Developing lice, or nymphs,take about 7 to 10 days to mature; afteran additional day, adult females startlaying eggs (Fig. 2). Consequently, thetotal life span of a head louse from eggthrough adult averages about 25 days.Because people have a constant bodytemperature, female lice reproducecontinuously throughout the year.

Head lice found in the United Statesprefer hair that is round in cross sec-tion. Hair that is ovoid in cross section,such as the extremely curly hair of Afri-can Americans, is not as attractive tolice that are adapted to round hairshafts. While head lice infestations arecommon in Africa, as in all continents,

Figure 1. Louse eggs (nits) attached tohair shafts.

nymph

egg

adult female(actualsize)

Figure 2. Life cycle of head louse.

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African head lice have claws especiallyadapted for grasping oval hair shafts.The African variety of head lice is notcommon in North America and conse-quently African Americans are muchless susceptible to infestations, but theycan get head lice.

MANAGEMENTHead lice are not known to transmitany infectious diseases from person toperson. They are more of a nuisancethan a health risk problem. It is veryimportant that the methods used tocontrol a head louse infestation notcause more of a problem than the headlice themselves. One major problem fora child with head lice is that they willnot be allowed to attend school as longas nits can be found in their hair.

Nits are most effectively removed bycombing the hair with a specially de-signed nit comb. Consider shampootreatments only when active lice orviable eggs are observed. Although liceand their eggs may be seen withoutmagnification, the viability of eggscannot be judged without proper mag-nification and some knowledge ofwhat hatched and unhatched eggs looklike. For color photos of nits in variousstages of development, see the Website listed under “Online Resources.”

There are four critical steps to control-ling an infestation of head lice:• the use of an effective head louse

treatment;• nit removal from the head (combing);• removal of lice and nits from the

household environment by vacuum-ing, washing, or freezing objectssuspected of being infested; and

• daily head checks and nit removaluntil infestation is gone, followed byweekly head checks to detectreinfestation.

Head Lice InsecticidalShampoosHead lice shampoos contain insecti-cides and if they are not used properlycan cause problems in and of them-selves. In addition, resistance to theinsecticides in the shampoos amongpopulations of head lice is becomingan increasing problem. Most of the

over-the-counter products containeither pyrethrin or permethrin (NIXand Rid). In the past a popular productfor the control of head lice was a prod-uct called Kwell, which contains theinsecticide lindane. Lindane has beenassociated with a variety of adversereactions suffered both by people beingtreated and by people applying thetreatment. It is also a troublesome pol-lutant of wastewater and requires spe-cial treatment to be removed. Whilelindane is still available by prescrip-tion, pyrethrin and permethrin aresafer, more effective, and less pollutingthan lindane.

When using a head louse shampoo,minimize body exposure by confiningthe insecticide to the head hair. Do notuse it in the bath or shower, but washthe infested person’s hair in a basin orsink so insecticide residues do notreach other parts of the body. The per-son doing the treatment should wearrubber gloves. Never apply an insecti-cide to anyone who has open cuts,scratches, or inflammations, and neveruse these materials on infants withoutconsulting a doctor. In all cases, followlabel directions completely andcarefully.

While pyrethrin and permethrin arefairly effective, they do not kill all theeggs. In addition, they may not kill allthe nymphs and adults, especially ifthe population is developing resistanceto the insecticide. Lice should diewithin 10 to 30 minutes after treatmentwith pyrethrin or permethrin. If youfind live lice after 30 minutes, suspectthat resistance is occurring and discon-tinue use of that product. If you need afollow-up treatment at the recom-mended interval on the product label,use a pyrethrin if you used permethrinthe first time, or vice versa, but do notresort to dangerous practices such asapplying other insecticides, pet fleaand tick shampoo, or materials such askerosene!

You will still need to supplementshampoo treatment with combing thehair (as described below) and somecleaning of the house and personaleffects likely to be infested. If you do

not remove nits with hair combing, theinfestation will reoccur and the addi-tional use of the treatment productswill increase the treated person’s expo-sure to these insecticides, as well ashelp select for resistance in the headlouse population.

If you want to avoid insecticides en-tirely, you could try using soap sham-poos that contain coconut or olive oils.Most soaps kill all stages of the louseexcept the egg. Four shampoos, eachabout 3 days apart, should kill most ofthe lice as each successive shampookills newly hatched nymphs. Alwayscombine shampooing with daily comb-ing and a cleaning of the environment.

Enzymatic treatments, including sham-poos that claim to dissolve eggs, thecement that attaches eggs to the hair,or the exoskeleton of the adults, arealso available to use against head lice.Although these materials are very ap-pealing because of their relativenontoxicity, in university-conductedresearch trials none of them has yetproven to work as advertised.

While shampoos with coconut oil mayhelp in controlling infestations of headlice, they are not effective as a repellentagainst lice to prevent infestation orreinfestation.

Hair CombingCombing the hair to remove nits andlice that survived the shampoo treat-ment is the key to successfully control-ling this pest. This process is timeconsuming but critical for success. Ifyou do not completely remove all nits,reinfestation will most likely occur.This process should be repeated dailyas long as nits and lice are still foundon the head. Many people use nitcombs to remove nits from the hairshaft. The most effective nit comb is ametal one specially designed for re-moving head lice and their eggs; plas-tic combs, even the ones that comewith the lice shampoos, are not as ef-fective. Metal lice combs can be foundat drug stores or ordered from the Na-tional Pediculosis Association, Inc.,listed in “References,” which has aspecially designed nit comb called the

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LiceMeisterTM. The infested hair canalso be cut out with small safetyscissors.

The person to be treated should beseated near a good light source. Thematerials you will need for hair comb-ing are• a box of tissues and plastic bag;• a good nit comb or a pair of safety

scissors;• a lamp that allows you to direct it to

the area you are working on;• hair clips to pin up the sections of

hair that have been combed; and

• something to entertain the personbeing treated—especially if it is achild.

Following the use of a head louseshampoo, use regular shampoo andconditioner to wash the hair (the hotterthe water the better because lice arevery vulnerable to high temperatures,but be careful not to hurt young chil-dren whose scalps are more sensitiveto hot water than scalps of olderpeople). Leave the conditioner in andtowel dry the hair. Then comb the hairusing a regular comb to remove snarlsand the accumulation of any suds.

Starting at the crown of the head, sepa-rate out a section of hair that is about 1inch by 1⁄2 inch; hold it out from thehead (Fig. 3). Insert the louse comb atthe base of the hair section as close aspossible to the scalp, and pull the combslowly through the hair. Be sure toslant the comb so that the curved sideof the teeth is towards the head. If youaren’t using a comb, go through eachsmall section of hair and use your fin-gernails to pull the eggs off the hair, orcut the individual hairs off. Use thetissues to clean any lice or debris fromthe comb following each combing or tocollect nits and hair that are removed,and put the tissue in the plastic bag.Continue to comb the section of hairuntil you feel sure it is free of nits orlice, then pin it out of the way with ahair clip and start on the next section ofhair. If the hair dries during the comb-ing process, wet it again with water toreduce pulling and hair loss. When allthe hair has been combed, rinse it thor-oughly with water and then dry. Afterthe hair is completely dry, check theentire head for stray nits and removethem individually.

To clean up, soak the comb in hotsoapy ammonia water for 15 minutesor boil it for 15 minutes (only the metalones). An old toothbrush is useful inremoving the debris that is lodged inthe teeth of the comb, as is dental floss.The plastic bag should be sealed anddisposed of.

It is not necessary to cut a person’s hairif they become infested with lice. How-

ever, the shorter the hair, the easier it isto comb for lice. If successive treat-ments for lice have been made and theinfestation persists, or if you want tocontrol the infestation quickly, this isan option to consider.

Cleaning Your HomeIt is important to wash the clothing andbedding of the infested person at thetime he or she is initially treated. Headlice will be killed if infested articles arewashed in hot water (at least 140°F)and dried in a hot dryer. If an articlecan’t be washed, have it dry cleaned.Another alternative that works well forheadgear such as earphones and bikehelmets is to place them in a plastic bagand put them in a freezer. If the freezeris 5°F or lower, all lice and eggs shouldbe dead within 10 hours. Also cleanother personal items such as stuffedanimals, car seats—any object thatmight have come in contact with theinfested person’s head. Vacuumingcarpets and upholstery will effectivelyremove hair containing nits in theseareas. While it is important to cleanobjects that come in contact with thehead, in general lice stay on the head.Therefore it is not necessary to go into afrenzy of house cleaning and it is espe-cially not necessary to use any insecti-cide to spray rooms or objects. Timeand effort are much better spent comb-ing nits and lice from the hair.

Contacting Friends andthe SchoolIt is important to contact anyone yourchild has had close contact with in therecent past to let them know of a headlouse infestation. The reason for this issimple: the infestation came fromsomewhere, and if the source or otherrecently infested people are not treated,your child can become reinfested whencontact is renewed. That means youwill need to go through all of the abovetreatment procedures again.

Nits are laid at the junction of the scalpand hair shaft, and they hatch in 7 to 11days. The average growth rate of hu-man hair in children is 0.4 mm per day,so by the time the nit has hatched it hasmoved about 2 to 3 mm away from thescalp. Therefore, nits further than 1⁄4Figure 3. Combing for head lice.

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August 2001 Head Lice

For more information contact the University

of California Cooperative Extension or agri-

cultural commissioner’s office in your coun-

ty. See your phone book for addresses and

phone numbers.

AUTHORS: M. K. Rust, J. H. Klotz, N. C.

Hinkle, and S. Klotz

EDITOR: B. Ohlendorf

TECHNICAL EDITOR: M. L. Flint

DESIGN AND PRODUCTION: M. Brush

ILLUSTRATIONS: Fig. 1 and 2: Adapted

from drawings by S. Klotz; Fig. 3: J. L.

Lockwood

Produced by IPM Education and Publica-

tions, UC Statewide IPM Project, University

of California, Davis, CA 95616-8620

This Pest Note is available on the World

Wide Web (http://www.ipm.ucdavis.edu)

This publication has been anonymously peerreviewed for technical accuracy by University ofCalifornia scientists and other qualified profes-sionals. This review process was managed by the

ANR Associate Editor for Pest Management.

To simplify information, trade names of productshave been used. No endorsement of named productsis intended, nor is criticism implied of similar productsthat are not mentioned.

This material is partially based upon worksupported by the Extension Service, U.S. Departmentof Agriculture, under special project Section 3(d),Integrated Pest Management.

WARNING ON THE USE OF CHEMICALSPesticides are poisonous. Always read and carefully follow all precautions and safety recommendations

given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed,away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especiallygardens containing fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Eitheruse the pesticide according to the label or take unwanted pesticides to a Household Hazardous WasteCollection site. Contact your county agricultural commissioner for additional information on safe containerdisposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose ofempty containers by following label directions. Never reuse or burn the containers or dispose of them in sucha manner that they may contaminate water supplies or natural waterways.

The University of California prohibits discrimination against or harassment of any person employed by orseeking employment with the University on the basis of race, color, national origin, religion, sex, physicalor mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status,age, sexual orientation, citizenship, or status as a covered veteran (special disabled veteran, Vietnam-eraveteran, or any other veteran who served on active duty during a war or in a campaign or expedition for whicha campaign badge has been authorized). University policy is intended to be consistent with the provisionsof applicable State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may bedirected to the Affirmative Action/Staff Personnel Services Director, University of California, Agriculture andNatural Resources, 300 Lakeside Dr., Oakland, CA 94612-3350; (510) 987-0096.

inch from the scalp have probablyhatched and are no longer viable. Forthis reason, the “no nit” policy in placeat many schools does not have a bio-logical basis, but most schools do nothave personnel with expertise in dis-tinguishing the viability of nits.

If head louse infestations are occurringat your child’s school, check yourchild’s head nightly using a metal licecomb and a good light source. Theearlier an infestation is discovered, theeasier it will be to treat. Avoid unnec-essary treatments with head louse in-secticides; use them only when lice orlouse eggs have been found on achild’s head to minimize the child’sexposure to these materials. Also, theuse of pesticide products can be harshon a child’s hair and very drying to thescalp, which in turn can cause an in-

crease in dried scalp flakes and dan-druff that might be mistaken for nits.Remember, nits are glued to the hairshaft and are not easily removed; theyare oval-shaped and glued at an angleto the side of the hair. If in doubt, use agood magnifying lens to verify a sus-pected nit or louse (and compare whatyou find to the photos on the Web sitelisted under “Online Resources”) be-cause pesticide treatment is not appro-priate for hair debris.

REFERENCES ANDRESOURCESEbeling, W. 1975. Urban Entomology.Oakland: Univ. Calif. Agric. Sci. pp. 455-459.

Hitchcock, J. C., R. M. Davis, and V.Kramer. March 1996. Head lice (Pedicu-lus humanus capitis): A heady, nitpicky,

and lousy problem. Calif. Morbidity.Berkeley: Div. Communicable DiseaseControl.

National Pediculosis Association, Inc.,P.O. Box 610189, Newton, MA 02161.Phone: 617-449-NITS. Online: http://www.headlice.orgTo order a nit comb call 1-888-542-3634.

Wilson, B. 1995. Ectoparasites. InMandell G. L., J. E. Bennett, and R.Dolin, eds. Principles and Practice ofInfectious Diseases. New York: ChurchillLivingstone, pp. 2558–2560.

Online ResourcesPollack, R. J. Head lice information.www.hsph.harvard.edu/headlice/photos.html