Structural and Public Health Pests: Head Lice

Pest Management In and Around Structures October 13, 2009 Print Friendly and PDF



In the US, there are between 6 to 12 million cases each year, most commonly among children three to twelve years of age. Head lice (Pediculosis capitis) are not a sign of uncleanliness and do not vector disease organisms. However, scratching can lead to secondary bacterial skin infections. The most common symptoms are itching and sleeplessness. Head lice cases can result in extreme anxiety, embarrassment, unnecessary days lost from school and pesticide exposure. Millions of dollars are spent on remedies annually.

The adult louse is 2 to 3 mm long (the size of a sesame seed); color varies. The female lives for 3 to 4 weeks and lays approximately 10 eggs (nits) a day. The eggs are firmly attached to the hair shaft close to the scalp. Viable nits are camouflaged with pigment to match the hair color of the infested person. They are most easily seen at the hairline at the back of the neck. Empty egg casings are easier to see, appearing white against the hair.

Eggs are incubated by body heat and hatch in 10 to 14 days. After hatch, nymphs leave the shell casing and grow for about nine to twelve days before reaching the adult stage. If left untreated, the life cycle may repeat every three weeks.

Lice feed by injecting small amounts of saliva and removing tiny amounts of blood from the scalp every few hours. The saliva may create an itchy irritation. The first case of head lice an individual has may not result in itching for four to six weeks. Once sensitized, subsequent infestations cause itching almost immediately.

Head lice usually survive for less than two days if away from the scalp at normal room temperature. Eggs cannot hatch at an ambient temperature lower than that near the scalp. Laundering and drying clothing and bedding at 130oF will kill all stages.

Monitoring and inspection for head lice

Screening for head lice in schools is a very useful role for the school nurse. Active infestations need to be addressed individually. Providing information to families on the diagnosis, treatment and prevention of head lice extends benefits beyond the school environment.

An adult louse can move six to 30 cm per minute. They are hard to see and very difficult to remove. Nits are easier to spot, especially at the nape of the neck or behind the ears. Unhatched eggs will be within 1 cm of the scalp. In general, nits found more than 1 cm from the scalp are unlikely to be viable, but in warmer climates viable nits can occur farther from the scalp. However, screening for nits is not an accurate way of predicting which children will become infested. Only approximately 18% of children with nits alone will convert to an active infestation (Williams et al. 2001). Children with 5 or more nits within 1 cm2 of the scalp are significantly more likely to develop an infestation, still only 1/3 of these higher-risk children convert. Generally, around 30% of school children with nits will also have adult lice.

The presence of active lice on a child‘s head is the only definitive indication of an infestation that should trigger a head treatment. If an active infestation is noted, the child‘s parent or guardian should be notified immediately. Treatment options may be suggested. Other members of the family should inspect each other along with children who regularly sleep-over or share hair apparel (hair clips, head-sets, hats, etc.). Parents and school nurses should be encouraged to recheck the student‘s head for lice after treatments have occurred if the child is still symptomatic.

The American Academy of Pediatrics and the National Association of School Nurses ( discourage no nit policies in schools. There is no need to send students home.

Cultural and physical options for head lice

Due to the short time period that head lice can survice off the head, transmission may occur most commonly with head-to-head contact which should be avoided. To further reduce potential for transmission, discourage sharing of combs, brushes, headbands, barettes, pillows, hats, scarves, coats, backpacks or other objects that may come in contact with the head. Where possible, place hats, scarves and coats on hooks or in separate lockers or cubbies to avoid contact. If hooks are shared or clustered, have children place their coats and hats in sealed plastic bags, especially if head lice are present. Hats and scarves can also be stored inside backpacks.

Manual removal of nits close to the head is always recommended. Fine-toothed "nit combs" are helpful. Combing and brushing wet hair damages lice and eggs significantly. Additionally, use of a hair dryer further injures adults, nymphs and nits.

Manual removal steps:

  1. Comb and divide hair into sections, use a metal fine toothed louse comb to remove nits and lice. After combing each section dip the comb in a container of hot soapy water to remove lice and nits.
  2. Repeat if nits are still attached within 1 cm of the scalp.
  3. Repeat until all the sections of hair have been systematically combed.
  4. Clean nit removal comb, clips, brushes, headphones, hats, etc. with hot soapy water.

Lice treatment kits often include nit removal aids. These are often lotions or sprays that are designed to help loosen the attachment of the egg on the hair shaft. Unfortunately, there is no independent scientific data indicating a benefit. For example, vinegar or vinegar-based products (e.g., Clear Lice Egg Remover Gel) can be applied to the hair for three minutes before combing out the nits. No clinical benefit has been demonstrated.

Occlusive substances including a "petrolatum shampoo" consisting of 30 to 40 g of standard petroleum jelly can be massaged onto the entire surface of the hair and scalp and left on overnight with a shower cap has been suggested. Diligent shampooing is usually necessary for at least the next 7 to 10 days to remove the residue. Other occlusive substances have been suggested (mayonnaise, tub margarine, herbal oils, olive oil) but benefits have not been demonstrated.

Table 1
Commonly used products for physical, cultural or mechanical management of head lice and uses.

Type Example Products Uses
combs LiceMeister® Comb NitFree Terminator™ Removes lice and nits.
botanical-based removal aid Lice-B-Gone® Eases removal by combing.

Pediculicide options for head lice

Most treatments for lice are shampoos left on the head for no more than 10 minutes. Most will not kill eggs so a second treatment is suggested. Removing nits close to the head is usually included in the treatment instructions. Most products warn against using the products on broken skin which is practically impossible given that lice-related itching usually leads to excoriation of the scalp which may be severe. If repeated treatments fail, some physicians will prescribe higher levels of permethrin (5%) or resort to scabies treatments (e.g. crotamiton, sulfamethoxazole, trimethoprim, ivermectin, etc.). These are extremely hazardous to children and not recommended.

Table 2 Commonly used pediculicide products for head lice.

Botanical formulations

Active ingredient Example Products Uses
Anise oil, coconut oil, and ylang ylang oil in an isopropyl alcohol carrier. Hair-Clean-1-2-3® Over the counter botanical reported to have a similar level of efficacy to Nix®. It has a very strong licorice smell and should be used with caution because of the high alcohol content making it highly flammable. The product is sprayed onto dry hair and left for 15 minutes. Then, lice and nits are removed with a metal nit comb (which comes with the product). A second application is suggested seven to ten days after the first. This product is most likely to be found in health food stores.

Formulations with greater potential hazards. Use less hazardous options.

Active ingredient Example Products Uses
permethrin (1%) Nix® Over the counter head louse treatment kits, including nit comb, etc. Currently the recommended treatment of choice by pediatricians. It has a lower mammalian toxicity than pyrethrins and does not cause allergic reactions in individuals with plant allergies. The product is a cream rinse applied to hair that is first shampooed with a non-conditioning shampoo, and then towel dried. It is left on for ten minutes and then rinsed off, and it leaves a residue on the hair that is designed to kill nymphs emerging. 20% to 30% of eggs are not killed with the first application. It is suggested that the application be repeated if live lice are seen seven to ten days later. Permethrin is a possible carcinogen according to US EPA.

Formulations with greater potential for acute toxicity. Use less toxic options (see above).

Active ingredient Example Products Uses
malathion (0.5%) Ovide® Prescription only organophosphate (cholinesterase inhibitor) lotion that is applied to the hair, left to air dry, then washed off after eight to twelve hours. Malathion has high ovicidal activity. Product directions suggest reapplication if live lice are seen in seven to ten days. The product has a high alcohol content making it highly flammable. There is an associated risk of severe respiratory depression.
lindane (1%) Kwell® 9160-3 Prescription only organochlorine that has central nervous system toxicity in humans; several cases of severe seizures in children using lindane have been reported. The shampoo should be left on for no more than 10 minutes; a repeat application is suggested after seven to ten days. Low ovicidal activity (30% to 50% of eggs are not killed).

Emerging issues, new strategies and priorities for head lice

Resistance has been reported to lindane, pyrethrins and permethrin. None of the currently available pediculicides are adequately effective against the egg stage.

Priorities for head lice.

  • Research
  • Efficacy of botanical pesticide products on head lice.
  • Thresholds for pesticidal treatment.
  • Effective, least-toxic ovicides.
  • Education
Support materials for schools offering reduced-risk treatment advice.
Effective head lice screening guidance, i.e. an emphasis should be placed on screening for nymph and adult head lice, not just nits. The threshold for pesticidal treatment should be the presence of nymphs and adults, or a specified number of nits per square cm of scalp.
  • Regulatory
Lindane is significantly more hazardous and significantly less effective than the over the counter alternatives. In 2003, the Food and Drug Administration (FDA) issued a Public Health Advisory concerning the use of topical formulations of lindane lotion and lindane shampoo for the treatment of scabies and lice. The warning states that lindane lotions and shampoos are to be used with caution in patients who weigh less than approximately 110 pounds (50 kilograms).
  • Management
Sound response strategies: stop all no-nit policies, pesticidal treatments of school environments (classrooms, dormitories, busses, etc.).

Additional resources for head lice management

  • Arizona Cooperative Extension. 2005. Head Lice. Pest Press. (PDF)
  • Center for Disease Control. 2008. Head Lice.
  • Frankowski, B.L., and L.B. Weiner. 2002. Head Lice. Pediatrics Vol. 110(3): 638-643.
  • Pollack, R.J. 2007. Harvard School of Public Health. Head Lice Information. Comprehensive website that answers many questions about and related to head lice including removal methods.
  • The American Academy of Pediatrics and the National Association of School Nurses

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.