4 pp., 3 photosThe three kinds of human lice (head lice, body lice, and pubic or crab lice) are described in this publication. There are guidelines for identifying lice and helpful instructions for preventing and controlling lice infestations

Moore, Glen C.

Olson, Jimmy K.

Texas A&amp;M Repository

Historically, human lice have been associatedwith wars, crowded living conditions, andpoverty. However, even in a peaceful, affluentsociety people can have louse infestations. This isparticularly true of head lice, which are most com-mon in preschool, kindergarten and elementaryschool children. According to the NationalAssociation of School Nurses, more than 6 millionAmericans are infested with head lice annually. Headlice are easily transferred between persons duringclose contact or when people share items such ashair brushes, combs, towels or hats. A person alsocan become infested by storing personal items inshared lockers or by using a head rest or high-backseat previously used by an infested person.Lice must have temperatures of 82 to 86 degrees F,favorable humidity, and a ready food source. So, theydo not leave the host unless they are dislodged or thehost’s body temperature drastically changes. Lice dieif separated from the host for more than 2 to 4 days.  The types of lice discussed here pierce the skin andfeed on blood. An infestation can cause persistentskin irritation and itching, which results in restless-ness and loss of sleep. The skin may become sensi-tized to the saliva and feces produced by lice.Scratching may open the skin and lead to secondaryinfection.   There are three kinds of human lice. Their commonnames describe their preferred feeding sites: headlice (Pediculus humanus capitis); body lice (Pediculushumanus humanus); and pubic or crab lice (Pthiruspubis). Human lice do not survive on pets or domes-tic animals. Adult lice are small (1.5 to 3 mm. in length), flat,wingless, greyish to brown insects. Their legs haveclaws for clinging to hair shafts.      Head LiceThe head louse adult is 2 to 3 mm long. Theabdomen is distinctly longer than it is wide. Colorvaries from dirty-white to greyish-black, but headlice usually blend in with the hair color of the host.Lice infesting blond people tend to be paler thanthose on people with black or brown hair.  Head lice prefer to live on the hair of the head, andare rarely found on other parts of the body. In asevere infestation, secretions produced by lice maycause the hair to become matted. The life cycle hasthree stages: egg (nit); nymph; and adult. The femalelays four to six nits per day or 50 to 150 eggs duringher lifetime. Eggs are oval, light tan in color, andabout the size of a fine particle of sand. Nits areglued to the base of hair shafts near the scalp, L-131507-06HUMAN LICEGlen C. Moore and J.K. Olson*Extension Agent–IPM, The Texas A&M University System; andProfessor of Entomology, Texas A&M University. Figure 1. Head louse (body louse looks the same).usually near the ears and on the back of the head.Eggs hatch in about 5 to 7 days under normal condi-tions.Newly hatched nymphs are transparent. They musttake a blood meal within 24 hours to survive, andmay take two to three blood meals per day. Over thecourse of about 9 days, immature lice pass throughthree nymphal stages and become straw colored asthey mature. They look much like the adults. The lifecycle is completed in 15 to 21 days and adults maylive up to 30 days. The presence of nits does not always mean that aperson has a current infestation. Nits may be leftfrom a previous infestation. Because eggs areattached to the hair shaft at the scalp, the position ofnits on the hair shaft can distinguish between pastand current infestations. In 1 week, the time it takesfor a louse egg to hatch, human hair grows about 1/4inch, carrying the egg with it. Therefore, eggs morethan 1/4 inch from the scalp either have alreadyhatched or will never hatch. Empty or hatched nitsmay remain attached to the hair shaft for months,but play no role in the transmission of head lice.They should be removed, however.Head lice are not known to cause any serious med-ical condition. Itching is the most common symptom.The greatest concern is the social stigma of having alouse infestation.Body LiceThe body louse looks much like the head louse, butis slightly smaller. It is often referred to as the com-mon clothing louse or “cootie.” Infestations of bodylice are more prevalent when a person’s hygiene ispoor and when clothes are worn continuously for upto several weeks or shared with others. Body lice arefound on clothing, particularly where garments comein close contact with the body, such as the crotch oftrousers, the waistline, and the armpits.The body louse’s life cycle is somewhat similar to thehead louse, except that a female may lay 270 to 300eggs during her lifetime or up to 10 eggs per day.Body lice glue their eggs to coarse fibers and innerseams of clothing, and occasionally to coarse hairs ofthe body. Eggs hatch in about 1 week. The life cycleis completed in about 27 days.Body lice remain on clothing except when feeding onthe host. In underdeveloped countries, body lice areknown to transmit louse-borne typhus and relapsingfever. Infestations are rare in developed countries.Pubic or Crab LiceCrab lice usually live in pubic hair, but may befound on the chest, in the armpits, on eyelashes andon beards. Crab lice are easily recognized by theircrab-like appearance. They vary in color from darkgrey to brown and measure about l.5 to 2.0 mm long.The body is nearly as wide as it is long. The secondand third pairs of legs are stout.Adults live 3 to 4 weeks. A single female will depositabout 26 eggs. Eggs hatch in 6 to 8 days and nymphsimmediately feed on the host. The immatures passthrough three nymphal stages before becomingadults. The life cycle is completed in 34 to 41 days.Crab lice are not known to transmit any diseases.Their bites produce bluish swellings on the skin.Crab lice are spread mainly through intimate physi-cal contact, so infestations are often associated withpromiscuity. It is possible that eggs on loose hairs lefton bedding and toilet seats may spread an infestationfrom one person to another.Figure 2. Eggs (nits) attached to hair.Figure 3. Crab louse.Preventing LiceThe best preventative is good hygiene.● Bathe daily. Thoroughly shampoo your hair several times each week.● Do not share hair brushes, combs, hats or headgear with others. Wash combs and brushesoften in hot, soapy water.● Machine wash bedding and clothing frequently.Or, have clothing dry cleaned.● Thick, long hair is ideal for head lice. If youhave long hair you can minimize head lice prob-lems by wearing your hair tightly braided andby thoroughly combing it each day.● Avoid close physical contact with anyone who is infested. Controlling LiceIf you know or suspect you have lice, seek help froma doctor, a school nurse, or the Texas Department ofHealth. Follow the advice and instructions youreceive. You will probably be advised to use a spe-cially medicated product (shampoo, lotion, hair rinseor mousse), as well as a fine-toothed louse comb, toremove lice. Such products are available over-the-counter and contain permethrin or pyrethrum plus piperonyl butoxide as the active ingredient. Otherproducts are available only by prescription.Head lice are sometimes hard to control, so be sureto follow the directions on the product label. Use thecorrect dose and apply it as directed. If a productdoes not seem to be working, switch to a productwith a different active ingredient. Also let your doc-tor and the Texas Department of Health know that atreatment product was not effective; it may be a signthat lice have developed resistance to the product.A second treatment must be made 7 to 10 days afterthe first to kill newly hatched lice. Without this sec-ond treatment, the infestation will continue.Shampoos containing coconut oil or olive oil are apopular alternative to insecticides. However, there isno research to show whether or not oils work, andremoving them from the hair can be difficult. Thereis no evidence that home remedies such as mayon-naise, margarine, Vaseline®, and food-grade oils areeffective. Never use dangerous products such asgasoline, kerosene, motor oil, household pesti-cides and pet shampoos.In addition to using a medicated product, it is a goodidea to remove lice and nits by hand. This can betime consuming. These tips will make the task easier.● Have the person sit under a bright light.● Brush the hair to remove tangles. ● Divide the hair into sections. Carefully examineeach section of hair for attached nits and lice.Using a fine-toothed lice comb, carefully workthrough each section from the scalp to the endsof the hair. Sections of hair not being workedshould be fastened aside.● Clean the lice comb frequently by dipping it inhot, soapy water. Use tape to remove nits anddebris from the comb.● Repeat the thorough examination every day for10 days, or until no more active lice or nits arefound.To control an infestation, you will need to wash bed-ding, clothing and towels in hot water (at least 125degrees F) for at least 10 minutes. For treating bed-ding and furniture that cannot be laundered or drycleaned, there are products labeled for such use.Thoroughly vacuum carpets, pillows and mattressesto remove fallen hairs with attached nits. Washbrushes and combs in hot (at least 125 degrees F),soapy water for about 20 minutes.Homes and schools should not be treated with insec-ticides. Lice do not hide in wall crevices and floorcracks like cockroaches and other household pests, sosuch treatments would be wasteful and ineffective.When a person has a louse infestation, it is criticalthat all family members and classmates be thorough-ly inspected and undergo simultaneous treatment ifnecessary. Almost all schools have a “no nit” policy,meaning that students who have infestations may notreturn to school until they are free of lice and nits.Parents should work closely with school nurses,teachers and administrators to handle infestations asdiscretely as possible so that children are not subject-ed to needless embarrassment.For further informationCaron, D. M. “Human Lice.” Publication No. HYG-42, Delaware Cooperative Extension Service. 1995.“Guidelines for the Treatment of ResistantPediculosis.” Publication No. OVD43899R,Harvard School of Public Health. 1999.The authors thank the following persons for their review of thismanuscript: Pat Morrison, Associate Department Head ofEntomology; Pete Teel, Professor of Entomology; and JohnJackman, Professor and Extension Entomologist; The Texas A&MUniversity System.Guillebeau, P. and G. A. Van De Mark. “Parent’sGuide to the ‘Nitty-Gritty’ about Head Lice.”Publication No. 851, University of GeorgiaCooperative Extension Service. 2000.Lyon. W. F. “Human Lice.” Publication No. HYG-2094, Ohio State University Extension Service.1996.Pollack, R. J. “Head Lice Information.” PublicationNo. 700K, Harvard School of Public Health. 2000.Shripat, T. K., D. L. Keith and W. L. Kramer. “HumanLice and Their Control.” Publication No. G86-789-A, Nebraska Cooperative Extension Service. 1993.Waldvogel, M. G. and C. S. Apperson. “Biology andControl of Human Lice.” Publication No. rsc-7,North Carolina Cooperative Extension Insect Note.1997.Produced by Agricultural Communications, The Texas A&M University SystemExtension publications can be found on the Web at: http://tcebookstore.orgVisit Texas Cooperative Extension at: http://texasextension.tamu.eduEducational programs of Texas Cooperative Extension are open to all people without regard to race, color, sex, disability, religion, age or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, andJune 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas Cooperative Extension, TheTexas A&M University System.Revision

Human Lice

Texas A&M University

H
istorically, human lice have been associated
with wars, crowded living conditions, and
poverty. However, even in a peaceful, affluent
society people can have louse infestations. This is
particularly true of head lice, which are most com-
mon in preschool, kindergarten and elementary
school children. According to the National
Association of School Nurses, more than 6 million
Americans are infested with head lice annually. Head
lice are easily transferred between persons during
close contact or when people share items such as
hair brushes, combs, towels or hats. A person also
can become infested by storing personal items in
shared lockers or by using a head rest or high-back
seat previously used by an infested person.
Lice must have temperatures of 82 to 86 degrees F,
favorable humidity, and a ready food source. So, they
do not leave the host unless they are dislodged or the
host’s body temperature drastically changes. Lice die
if separated from the host for more than 2 to 4 days.  
The types of lice discussed here pierce the skin and
feed on blood. An infestation can cause persistent
skin irritation and itching, which results in restless-
ness and loss of sleep. The skin may become sensi-
tized to the saliva and feces produced by lice.
Scratching may open the skin and lead to secondary
infection.   
There are three kinds of human lice. Their common
names describe their preferred feeding sites: head
lice (Pediculus humanus capitis); body lice (Pediculus
humanus humanus); and pubic or crab lice (Pthirus
pubis). Human lice do not survive on pets or domes-
tic animals. 
Adult lice are small (1.5 to 3 mm. in length), flat,
wingless, greyish to brown insects. Their legs have
claws for clinging to hair shafts.      
Head Lice
The head louse adult is 2 to 3 mm long. The
abdomen is distinctly longer than it is wide. Color
varies from dirty-white to greyish-black, but head
lice usually blend in with the hair color of the host.
Lice infesting blond people tend to be paler than
those on people with black or brown hair.  
Head lice prefer to live on the hair of the head, and
are rarely found on other parts of the body. In a
severe infestation, secretions produced by lice may
cause the hair to become matted. The life cycle has
three stages: egg (nit); nymph; and adult. The female
lays four to six nits per day or 50 to 150 eggs during
her lifetime. Eggs are oval, light tan in color, and
about the size of a fine particle of sand. Nits are
glued to the base of hair shafts near the scalp, 
L-1315
07-06
HUMAN LICE
Glen C. Moore and J.K. Olson*
Extension Agent–IPM, The Texas A&M University System; and
Professor of Entomology, Texas A&M University. Figure 1. Head louse (body louse looks the same).
usually near the ears and on the back of the head.
Eggs hatch in about 5 to 7 days under normal condi-
tions.
Newly hatched nymphs are transparent. They must
take a blood meal within 24 hours to survive, and
may take two to three blood meals per day. Over the
course of about 9 days, immature lice pass through
three nymphal stages and become straw colored as
they mature. They look much like the adults. The life
cycle is completed in 15 to 21 days and adults may
live up to 30 days. 
The presence of nits does not always mean that a
person has a current infestation. Nits may be left
from a previous infestation. Because eggs are
attached to the hair shaft at the scalp, the position of
nits on the hair shaft can distinguish between past
and current infestations. In 1 week, the time it takes
for a louse egg to hatch, human hair grows about 1/4
inch, carrying the egg with it. Therefore, eggs more
than 1/4 inch from the scalp either have already
hatched or will never hatch. Empty or hatched nits
may remain attached to the hair shaft for months,
but play no role in the transmission of head lice.
They should be removed, however.
Head lice are not known to cause any serious med-
ical condition. Itching is the most common symptom.
The greatest concern is the social stigma of having a
louse infestation.
Body Lice
The body louse looks much like the head louse, but
is slightly smaller. It is often referred to as the com-
mon clothing louse or “cootie.” Infestations of body
lice are more prevalent when a person’s hygiene is
poor and when clothes are worn continuously for up
to several weeks or shared with others. Body lice are
found on clothing, particularly where garments come
in close contact with the body, such as the crotch of
trousers, the waistline, and the armpits.
The body louse’s life cycle is somewhat similar to the
head louse, except that a female may lay 270 to 300
eggs during her lifetime or up to 10 eggs per day.
Body lice glue their eggs to coarse fibers and inner
seams of clothing, and occasionally to coarse hairs of
the body. Eggs hatch in about 1 week. The life cycle
is completed in about 27 days.
Body lice remain on clothing except when feeding on
the host. In underdeveloped countries, body lice are
known to transmit louse-borne typhus and relapsing
fever. Infestations are rare in developed countries.
Pubic or Crab Lice
Crab lice usually live in pubic hair, but may be
found on the chest, in the armpits, on eyelashes and
on beards. Crab lice are easily recognized by their
crab-like appearance. They vary in color from dark
grey to brown and measure about l.5 to 2.0 mm long.
The body is nearly as wide as it is long. The second
and third pairs of legs are stout.
Adults live 3 to 4 weeks. A single female will deposit
about 26 eggs. Eggs hatch in 6 to 8 days and nymphs
immediately feed on the host. The immatures pass
through three nymphal stages before becoming
adults. The life cycle is completed in 34 to 41 days.
Crab lice are not known to transmit any diseases.
Their bites produce bluish swellings on the skin.
Crab lice are spread mainly through intimate physi-
cal contact, so infestations are often associated with
promiscuity. It is possible that eggs on loose hairs left
on bedding and toilet seats may spread an infestation
from one person to another.
Figure 2. Eggs (nits) attached to hair.
Figure 3. Crab louse.
Preventing Lice
The best preventative is good hygiene.
● Bathe daily. Thoroughly shampoo your hair 
several times each week.
● Do not share hair brushes, combs, hats or head
gear with others. Wash combs and brushes
often in hot, soapy water.
● Machine wash bedding and clothing frequently.
Or, have clothing dry cleaned.
● Thick, long hair is ideal for head lice. If you
have long hair you can minimize head lice prob-
lems by wearing your hair tightly braided and
by thoroughly combing it each day.
● Avoid close physical contact with anyone who 
is infested. 
Controlling Lice
If you know or suspect you have lice, seek help from
a doctor, a school nurse, or the Texas Department of
Health. Follow the advice and instructions you
receive. You will probably be advised to use a spe-
cially medicated product (shampoo, lotion, hair rinse
or mousse), as well as a fine-toothed louse comb, to
remove lice. Such products are available over-the-
counter and contain permethrin or pyrethrum plus 
piperonyl butoxide as the active ingredient. Other
products are available only by prescription.
Head lice are sometimes hard to control, so be sure
to follow the directions on the product label. Use the
correct dose and apply it as directed. If a product
does not seem to be working, switch to a product
with a different active ingredient. Also let your doc-
tor and the Texas Department of Health know that a
treatment product was not effective; it may be a sign
that lice have developed resistance to the product.
A second treatment must be made 7 to 10 days after
the first to kill newly hatched lice. Without this sec-
ond treatment, the infestation will continue.
Shampoos containing coconut oil or olive oil are a
popular alternative to insecticides. However, there is
no research to show whether or not oils work, and
removing them from the hair can be difficult. There
is no evidence that home remedies such as mayon-
naise, margarine, Vaseline®, and food-grade oils are
effective. Never use dangerous products such as
gasoline, kerosene, motor oil, household pesti-
cides and pet shampoos.
In addition to using a medicated product, it is a good
idea to remove lice and nits by hand. This can be
time consuming. These tips will make the task easier.
● Have the person sit under a bright light.
● Brush the hair to remove tangles. 
● Divide the hair into sections. Carefully examine
each section of hair for attached nits and lice.
Using a fine-toothed lice comb, carefully work
through each section from the scalp to the ends
of the hair. Sections of hair not being worked
should be fastened aside.
● Clean the lice comb frequently by dipping it in
hot, soapy water. Use tape to remove nits and
debris from the comb.
● Repeat the thorough examination every day for
10 days, or until no more active lice or nits are
found.
To control an infestation, you will need to wash bed-
ding, clothing and towels in hot water (at least 125
degrees F) for at least 10 minutes. For treating bed-
ding and furniture that cannot be laundered or dry
cleaned, there are products labeled for such use.
Thoroughly vacuum carpets, pillows and mattresses
to remove fallen hairs with attached nits. Wash
brushes and combs in hot (at least 125 degrees F),
soapy water for about 20 minutes.
Homes and schools should not be treated with insec-
ticides. Lice do not hide in wall crevices and floor
cracks like cockroaches and other household pests, so
such treatments would be wasteful and ineffective.
When a person has a louse infestation, it is critical
that all family members and classmates be thorough-
ly inspected and undergo simultaneous treatment if
necessary. Almost all schools have a “no nit” policy,
meaning that students who have infestations may not
return to school until they are free of lice and nits.
Parents should work closely with school nurses,
teachers and administrators to handle infestations as
discretely as possible so that children are not subject-
ed to needless embarrassment.
For further information
Caron, D. M. “Human Lice.” Publication No. HYG-
42, Delaware Cooperative Extension Service. 1995.
“Guidelines for the Treatment of Resistant
Pediculosis.” Publication No. OVD43899R,
Harvard School of Public Health. 1999.
The authors thank the following persons for their review of this
manuscript: Pat Morrison, Associate Department Head of
Entomology; Pete Teel, Professor of Entomology; and John
Jackman, Professor and Extension Entomologist; The Texas A&M
University System.
Guillebeau, P. and G. A. Van De Mark. “Parent’s
Guide to the ‘Nitty-Gritty’ about Head Lice.”
Publication No. 851, University of Georgia
Cooperative Extension Service. 2000.
Lyon. W. F. “Human Lice.” Publication No. HYG-
2094, Ohio State University Extension Service.
1996.
Pollack, R. J. “Head Lice Information.” Publication
No. 700K, Harvard School of Public Health. 2000.
Shripat, T. K., D. L. Keith and W. L. Kramer. “Human
Lice and Their Control.” Publication No. G86-789-
A, Nebraska Cooperative Extension Service. 1993.
Waldvogel, M. G. and C. S. Apperson. “Biology and
Control of Human Lice.” Publication No. rsc-7,
North Carolina Cooperative Extension Insect Note.
1997.
Produced by Agricultural Communications, The Texas A&M University System
Extension publications can be found on the Web at: http://tcebookstore.org
Visit Texas Cooperative Extension at: http://texasextension.tamu.edu
Educational programs of Texas Cooperative Extension are open to all people without regard to race, color, sex, disability, religion, age or national 
origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and
June 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas Cooperative Extension, The
Texas A&M University System.
Revision


English

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Human Lice

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Human Lice

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