The head louse, infests 10-12 million people each year in the United States. Click here to learn about the biology of the head louse and the steps that you can take to prevent it's invasion of your home or school.

Adult Louse

Introduction

The head louse, Pediculus capitis DeGeer (Figure 1), infests 10-12 million people each year in the United States. Pediculosis or "lousiness" is one of the most prevalent communicable conditions in this country. Lice are primarily transferred from person to person by direct head to head contact or by several people using the same combs, brushes, hats, costumes, athletic equipment, towels, or bedding. Head lice are not found on animals or household pets and are not transmitted from pets to humans. Because of children’s play activity and close contact, head louse infestations are usually found on children, but can also be spread to adults. The head louse is not considered to be a serious vector of disease in the United States although severe infestations may cause irritation, scratching, and subsequent invasion of secondary infection from germs and lice feces. Itching from large numbers of bites may make the infested individual feel tired, irritable and feverish, thus the term “feeling lousy.”

CREDITS: James Castner, University of Florida Figure 1. Head louse, Pediculus capitis DeGeer.

Biology

Lice have three pairs of legs which makes them true insects. Lice do not have wings or powerful jumping legs so they move about by clinging to hairs with claw-like legs. Head lice prefer to live on the hair of the head although they have been known to wander to other parts of the body. Head lice feed every 4 to 6 hours so must remain in close contact with the host. While a louse may fall onto other surfaces, they cannot live there for more than 24 hours. Therefore, they do not normally live within rugs, carpet, furniture or school buses.

The eggs of lice are called nits. They are oval white cylinders (1/16 inch long). The eggs of head lice are glued to hairs of the head near the scalp. To protect the eggs from extremes in light and temperature, the female will commonly glue the eggs behind the ears and along the nape of the neck. Under normal conditions, the eggs will hatch in 7-10 days. The young lice which escape from the egg must feed within a few hours or they will die. Newly hatched lice will periodically take blood meals and molt three times before becoming sexually mature adults. A young louse will develop in 10-12 days to an adult (1/8 inch in length). Depending on climate and color of the host’s hair, adult lice range in color from white to brown to dark gray.

Female lice lay 6-7 eggs (nits) per day. She may lay up to 140 eggs during her 30 day lifetime. Adults cannot survive more than about 24 hours without a blood meal. The nymphs and adults all have piercing-sucking mouthparts which pierce the skin for a blood meal.

The reaction of individuals to louse bites can vary considerably. Persons previously unexposed to lice experience little irritation from their first bite. After a short time, up to a few weeks, individuals may become sensitized to the bites and react with a general allergic reaction including reddening of the skin, itching, and overall inflammation. Subsequent infestations usually cause itching and redness within 24-48 hours. Some individuals never exhibit symptoms.

Prevention of Head Lice

Head lice spread principally from person to person, like any contagious disease. Therefore, good hygienic practices can help prevent or lessen the duration of head louse outbreaks. Children, for example, should be encouraged not to share combs, hats, and other personal belongings. It is important to remember, however, that head lice are not necessarily associated with uncleanliness.

Periodic inspections aids in early detection of head lice. Early detection will prevent advanced infestations which are much more difficult to control. Children are best inspected during the early weeks of school (August - November) since outbreaks are most common during this time. For this reason, September is "National Head Lice Prevention Month".

Treatment of Head Lice

During outbreaks of head lice, in addition to stressing the preventative measures mentioned above, it is also be useful for students to bag their hats and coats between use, or keep them in personal lockers or at their chairs. Though head lice do not survive long away from their human host, they can crawl short distances, say, from one hat to another on a hat rack. Bean bag chairs or other stuffed furniture that children share should be removed temporarily from classrooms during outbreaks. Sharing of sports helmets and audio headphones can also contribute to the spread of head lice among students. Pesticides applied to classrooms, lockers or buses are generally ineffective for head louse control and should not be used.

Because of the biology of the head louse and its increasing resistance to available lice-killing (pediculicide) shampoos, relying on these products alone is not likely to be effective. An integrated approach, including the preventative measures mentioned above, regular head inspections by school nurses, advisories encouraging parents to do nightly head checks, manual removal with special louse and nit combs, and the judicious use of pediculicides is the best approach to managing infestations. Note that efforts to educate both kids and their parents about these pests and their control is a crucial part of a good IPM program for head lice.

Best Inspection Practices include:

• Use good lighting during your inspection. A lamp or good natural light from a window will work well.
• Use a hand lens or magnifying glass (10x). Magnification may help detect nits and lice.
• Shampoo hair. Do not use a product with conditioners in it if you are going to use a lice treatment product following your inspection and nit removal. See product label for more specific details.
• Remove tangles with a comb or hairbrush.
• Divide the hair in sections and fasten the hair that is not being worked on.
• If lice or nits are discovered, all family members and other contacts (babysitters, cousins, playmates, Sunday school teachers, etc.) should be inspected.
• Proceed to Best Nit Removal Practices (see below).
• Ideally, inspections and nit removal should be done daily for at least two weeks.

If you are a health care professional, screening many children for head lice, a magnifier lamp may be helpful. The magnifier and lamp are integrated into one unit and are usually circular or rectangular. They can be purchased from suppliers of scientific equipment, office furniture, art and quilting supply stores. You will also want to use disposable gloves and wooden screening sticks to maintain proper hygiene from head to head.

While we have no data to substantiate the effectiveness of products that claim to highlight nits so inspection is easier, we feel it is important to note that they are included in treatment kits. For example, "Neon Nits" (makers of Clear Lice System, Care Technologies, Inc.) claims to turn nits neon pink after application for easier inspection.

Cleaning the Environment

Once an infestation is detected through inspection, all clothes should be washed in hot soapy water (150F). Pillow cases, sheets, blankets and other bedding material should also be washed and placed in the clothes dryer on the "high heat" cycle for at least 20 minutes to kill the lice and their eggs. Carpets, furniture, car seats and any non-washable items such as children's toys should be thoroughly vacuumed and the vacuum bag immediately discarded outside of the home. Anything that cannot be vacuumed may be tightly sealed in plastic bags for at least 7-10 days to kill all stages of lice.

Best Nit Removal Practices

• After removing tangles and dividing hair into manageable portions, use a lice comb to remove nits and lice. Using a regular comb will not remove nits. Removing nits is a careful process where the hair is combed from root to tip with a special fine-toothed louse comb. Plastic combs are not as good as metal louse combs.
• Comb from scalp to the end of the hair.
• Dip comb in a container of hot soapy water to drown lice and remove nits.
• Look through that same section of hair for remaining nits and lice and repeat combing section, if necessary.
• Repeat all steps until all hair is systematically combed through.
• Clean nit removal comb, clips, brushes and other tools used with hot soapy water or if using a metal comb, rubbing alcohol. An old toothbrush may help dislodge hair, nits and lice that may be caught in the teeth of the comb. Plastic combs and toothbrushes should be sealed in a plastic bag and discarded after use.
• Areas around the nit combing area should be vacuumed and the vacuum bag immediately discarded.
• Nit removal is key to controlling head lice because 20 to 80% of nits can still be alive after shampooing with pyrethrin or permethrin based products.

Nits are difficult to remove because they are cemented onto the hair. There are several products available that claim to loosen nits. Many products are included in lice treatment kits. Again, we do not have data to substantiate claims of effectiveness, but thought it was important to address them.

• RID products include an "egg and nit comb-out gel."
• Clear Lice Elimination System also sells a "natural lice egg remover" in the form of a "vegetable-derived enzyme mousse."
• Vinegar and water mixed in a 1 to 1 ratio is commonly applied to the head and allowed to soak for 30 to 60 minutes.
• Although difficult to wash out, alternative treatments using vegetable oil, mayonnaise or petroleum jelly are also reported to make combing nits out easier.

Chemical Control

Pediculicides available in the United States include prescription lindane and malathion and over the counter (OTC) pyrethrins and permethrin. Note that lindane is an organochlorine that will accumulate in human tissue and if misused, may be toxic to the nervous system. Even if lice are not managed after the prescribed application of lindane, prescriptions should not be refilled. Malathion is an organophosphate which has an 8-12 hour application time. The carrier is highly flammable, so care must be taken during application. Caution must be exercised when using these prescription products and the label should be followed exactly. The OTC pyrethrins include generic products as well as those listed in Table 1. Many insecticides, including some pediculicides will degrade over time and excess material should not be stored, but discarded after application.

Best Head Lice Treatment Practices:

Table 1 lists some over-the-counter products available for head louse control. Please read the product labels carefully. Pay careful attention to warnings and disclaimers.

Table 2 lists some prescription products available for head louse control.

Prescription only products containing 1% lindane come in topical shampoos, creams, and lotions under the names of Kwell, Kildane, and Scabene to name a few. These products have the potential to adversely affect the human central nervous system if used incorrectly. These products do not kill nits effectively and there have been worldwide reports of resistance.

Several other products such as Elimite (5% permethrin; Allergan, Irvine, CA) and Eurax (10% crotamiton; Westwood-Squibb Pharmaceuticals, Buffalo, NY) have been listed on some websites as possible treatments for head lice. However, these products are not approved by the FDA at this time for lice control.

Suffocant Treatment as an Alternative

Suffocants such as oil, mayonnaise or petroleum jelly have been applied to the hair in an effort to suffocate head lice. There is little scientific evidence to support the effectiveness of suffocant treatments. However, people turn to alternative treatments when they feel conventional treatments do not work, when they have toxicity concerns with conventional treatments or they cannot afford conventional treatments. While we do not have data to substantiate claims of effectiveness for suffocants, we feel it is important to address them. In general, suffocants are used by:

• Applying generously to the hair.
• Covering the hair with a shower cap for several hours. Do not use this method of covering the hair overnight, as it is a suffocation hazard to the person being treated.
• Shampooing hair to remove most of the suffocant.
• Removing nits and lice as discussed in Best Inspection Practices and Best Nit Removal Practices.
• Washing hair thoroughly with shampoo to remove remaining suffocant.

Caution: If you are planning to use a treatment containing a pesticide, it is NOT recommended that you use the suffocant method concurrently. Oils can increase the penetration of pesticide product through the skin over prolonged periods of time. One small study that we were able to find submerged lice in olive oil for one hour (6 lice) and two hours (6 lice). Survival was compared to lice that were not submerged (6 lice). All lice that were not submerged or were submerged for 1 hour survived. Two of the 6 lice submerged for 2 hours died. This is a very small test and the researchers cautioned against extrapolating the data to infestations on humans (Spielman 2000).

Over-the-counter products available for managing head lice

1. Kit can include comb for nit removal, gloves for washing hair, etc.
2. Most are shampoos that should be left in the hair for 10 minutes before rinsing. Rinse head over a sink with cool water to minimize product exposure. Rinsing in the shower increases exposure because shampoo is distributed as water runs down body. Hot water increases exposure because it may increase penetration through skin. May require a second treatment 7 to 10 days later because 20 to 30% of nits can survive the initial treatment. Use gloves while washing hair with these products. Proceed to nit removal.
3. Contains Coconut Oil, Anise Oil and Ylang Ylang Oil, Isopropyl Alcohol. Data cited in Meinking, T. A. 1999. Infestations. Curr. Probl. Dermatol. 11:73-120. These data indicate that HairClean 1-2-3 is as effective as Nix.
4. Wash hair with non-conditioning shampoo. Work creme rinse into hair and leave on for 10 minutes. Creme rinse residue is supposed to last in hair up to 10 days, thus killing emerging nymphs. Proceed to nit removal.

Prescription only products for management of head lice

1. Apply Ovide lotion to dry hair.
2. Allow hair to dry naturally. This product contains alcohol and it is flammable.
3. Shampoo hair after 8 to 12 hours or as directed by physician.
4. Proceed to nit removal.

Frequently Asked Questions

1. What's the difference between pyrethrins and permethrin? Pyrethrins are naturally occurring compounds extracted from chrysanthemum plants. Insects possess mechanisms to break down pyrethrins so a synergist, piperonyl butoxide, is usually added to the formula which inhibits the insect's ability to break down the pyrethrins. Permethrin has the same basic chemical make-up but is synthetically enhanced to be more effective. Permethrin has much longer residual activity and does not require the use of a synergist.
2. Can lice be transmitted from my dog or cat to my children? No. Head lice are specific to humans. They can only survive on a human host. If a head louse is removed from its host, it will die within a day or two.
3. How big are lice? An adult head louse is approximately 2.5-3.5 mm long. A louse egg, or "nit" is roughly 0.5-1.0 mm long.
4. I've heard that head lice are resistant to some of the lice treatments; is this true? In some locations there have been reports of potential resistance to several different pediculicides (lice killing agents). Experts are currently researching this issue and are trying to determine to what extent resistance exists. The best way to avoid this situation is to follow the directions on the product label closely. Improper application of pediculicides has significantly contributed to the presence of resistance in lice.
5. How long do lice live? A louse egg hatches about 10 days after being glued to a hair shaft. Upon hatching, a louse will molt three times over a 10-12 day period before molting into a mature adult. An adult louse can live up to 40 days.
6. How long after my child contracts lice will I be able to detect them? It only takes one adult female louse to begin an infestation. A female louse can lay several eggs each day. Within a couple of weeks a child may have dozens of immature lice living on his/her head. The more lice present, the more quickly the child will begin feeling an "itchy" scalp which would usually lead to an inspection by a parent or school official. Looking for one louse or one nit might be difficult but dozens should be readily apparent through close inspection.

References

Frankowski, B. L., L. B. Weiner. 2002. Head Lice. Pediatrics 110: 638-643. (A clinical report by the American Academy of Pediatrics, Committee on School Health and the Committee on Infectious Diseases, issued September 2002.)

Spielman, A. 2000. Head Lice Information. Harvard School of Public Health. http://www.hsph.harvard.edu/headlice.html

Footnotes

1. This document is ENY-296, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Originally authored by C. Scherer, P. G. Koehler and F. M. Oi. Publication date: August 1997. Revised: April 2007. Please visit the EDIS Website at http://edis.ifas.ufl.edu. Additional information on these organisms, including many color photographs, is available at the Entomology and Nematology Department Website located at http://entnemdept.ifas.ufl.edu.
2. R.W. Baldwin and F. M. Oi, assistant extension scientists, Entomology and Nematology Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

Original Content Authors: R.W. Baldwin and F. M. Oi