Head Lice

The Organism

The adult head louse is 2-3 mm long (size of a sesame seed); has 6 legs and is tan to grayish- white in color.

The female lives up to 4 weeks and when mature lays up to 10 eggs/ day.

Eggs are attached to base of the hair shaft ~4 mm from scalp. Viable eggs camouflaged with pigment to match the hair color of the infested person are often most easily seen at the posterior hairline.

Empty egg casings (NITS) are easier to see as they appear white against the darker hair. The term “NIT” is used in some articles to mean both viable eggs and empty egg cases leading to potential confusion.

Eggs are incubated by body heat and typically hatch in 8-9 days, but can range from 7-12 days depending on the ambient climate being hot or cold. Upon hatching, the nymph undergoes developmental stages reaching adulthood within 9-12 days. The female louse can mate and begin to lay viable eggs within 1.5 days of becoming an adult. Untreated, this cycle may repeat ~ every 3 weeks.

The louse feeds by injecting small amounts of saliva with blood vessel dilating and anti-clotting properties and sucking tiny amounts of blood from the scalp. Itching results from an allergic reaction to components of the saliva. With a first case of head lice, itching may not occur for 4-6 weeks as it takes that long for the infested person to become sensitized and begin to have the allergic reaction.

Head lice cannot survive away from the scalp at room temperature for greater than 24 hours and their eggs cannot hatch at an ambient temperature lower than that near the scalp.

Head lice do not transmit any disease agent. Areas of the scalp that are scratched can get secondarily infected (impetigo) and this may prompt lymph-node enlargement in the upper posterior neck.


Head lice infestation is most common among pre-school and elementary school aged children, but all ages can be affected.

All Socioeconomic Groups Are Effected!

Infestation is not influenced by hair length or frequent brushing or shampooing. In cultures such as the U.S., where daily hair brushing is routine, infested individuals rarely have more than a dozen live lice.


Lice cannot hop or fly; they crawl. Transmission in most cases occurs by direct contact with head of an infested individual. Indirect spread through contact with the personal belongings of an infested individual (combs, brushes, hats) is much less likely, but may occur rarely. It has been shown that lice on combs are usually dead and that live lice are rarely found on potentially shared items such as pillow cases.

The major focus of control activities should be to reduce the number of lice on the head and to reduce head-to-head contact.


The Gold standard is finding a live louse on the head which can be difficult as lice avoid light and crawl quickly. Using a louse comb and water, oil or conditioner to slow the lice down may be helpful. The tiny eggs may be easier to see at the nape of the neck or behind the ears within 1 cm of the scalp.

It is important not to confuse eggs or nits with dandruff, hair casts, hairspray droplets, etc. Eggs found greater than 1 cm from the scalp are unlikely to be viable.



NIX-Permethrin (1%)-OTC

  • May occasionally cause minor local skin irritation
  • Apply to damp hair that has just been shampooed with a non-conditioning shampoo and towel dried. Rinse off after 10 minutes.
  • Repeat on day 9 or alternatively on days 0, 7, 13-15.
  • Resistance varies from area to area

RID-Pyrethin plus Piperonyl Butoxide-OTC

  • Remote possibility of allergic reaction in persons allergic to ragweed or chrysanthemums
  • Apply to dry hair and rinse out after 10 minutes.
  • Repeat on day 9 or alternatively on days 0, 7, 13-15
  • Resistance varies from area to area

OVIDE-Malathion (0.5%)-by prescription

  • Highly flammable; do not use hair drier, curling iron or smoke near child while hair is wet.
  • Not approved under age 6 years
  • Apply to dry hair and wash off after 8-12 hours
  • One application usually sufficient; repeat in 7-9 days if live lice seen
  • Resistance is currently rare

ULEFSIA-Benzyl Alcohol (5%)- by prescription

  • Approved for children older than 6 months
  • Apply to damp hair and rinse off after 10 minutes
  • Repeat day 9 or alternatively on days 0, 7, 13-15
  • Resistance is currently not documented

Lycelle-Cytanyl5 and other ingredients

  • Approved for 2 years and older
  • Apply to dry hair and saturate scalp and entire length of all hair.
  • Leave on for 10 minutes and then shampoo out
  • Kills lice and eggs
  • Repeat treatment 7-10 days to ensure cure
  • May need 2 bottles(100ML) for hair longer than shoulder length
  • Works by damaging waxy outer layer of lice and eggs
  • Resistance not currently documented
  • Kit comes with nit comb

Natroba-Spinosad 0.9% Suspension and Benzyl alcohol

  • Approved for children older than 4 years
  • Apply to dry hair for 10 minutes and then shampoo out
  • Saturate scalp and entire length of all hair
  • Repeat treatment in 7-10 days
  • May need 2nd bottle(120 ml) for hair longer than shoulder length

Kwell-Lindane( 1%)- by Prescription

Potential neurotoxin and no longer recommended except for patients who have not responded to or who cannot tolerate other routine treatments.

Removal of Pediculicides

  • Rinse over sink rather than shower or bath to limit skin exposure
  • Use warm water rather than hot to minimize absorption attributable to vasodilation

Topical Reactions

Itching or burning sensation of the scalp may be due to a reaction to the drug used and may persist for several days after the lice are killed. This should not be considered a reason for re-treatment. Oral anti-histamines and topical corticosteroids may be helpful for these symptoms.

“Natural” Products

Essentials oils and other plant extracts are marketed for treatment of head lice but their safety and efficacy are not regulated by the FDA and therefore, cannot be officially recommended.

Occlusive Agents

  • Petroleum jelly or mayonnaise liberally applied and left on overnight under a shower cap has been reported anecdotally to be effective in suffocating lice.
  • Cetaphil cleanser applied and then dried with a hair drier has been anecdotally reported as effective.

Manual Removal

  • Removal of nits immediately after treatment with a pediculicide is not necessary to prevent spread because only live lice cause an infestation.
  • Nit removal can be difficult and tedious even with special nit combs. Electric oscillating louse combs and products that claim to dissolve the “glue” that binds the nit to the shaft of the hair are all of unproven benefit or efficacy.

Pediculicide Resistance

  • No pediculicide is 100% effective in killing the eggs; resistance varies from area to area
  • Possible causes of incorrect diagnosis of resistance include: misdiagnosis, inadequate amount of product used, re-infestation from untreated classmate and failure to properly time re-treatments.

Environmental Interventions

  • If a person is identified with head lice, all family members should be checked and those found with live lice or nits within 1 cm of the scalp should be treated. It is prudent to treat family members who share a bed with the infested person even if no live lice are found.
  • While transmission on shared items is less likely than head-to-head contact, cleaning hair care items, pillow cases seems prudent.
  • Other items with potential head contact such as headgear, furniture, carpeting, rugs, car seats can be considered for cleaning/vacuuming.
  • Washing, soaking or drying items at 130 degrees F will kill nits/lice
  • Pediculicide sprays are not needed or recommended.
  • Items that cannot be washed can be bagged for 2 weeks.
  • Herculean cleaning measures are not needed!!!

Management on the Day of Diagnosis

  • Because a child with an active head lice infestation likely has had the infestation for a month or more by the time it is discovered and poses little additional risk to classmates, the child should remain in school. His parents should be discreetly notified and treatment initiated that afternoon or evening.
  • The child may return to school the day after effective treatment has been initiated.
  • The presence of nits greater than 1 cm from the scalp should NOT be a reason for school exclusion.