Clinical Pediatric Associates

(214) 368-3659

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

RID-Pyrethin plus Piperonyl Butoxide-OTC

OVIDE-Malathion (0.5%)-by prescription

ULEFSIA-Benzyl Alcohol (5%)- by prescription

Lycelle-Cytanyl5 and other ingredients

Natroba-Spinosad 0.9% Suspension and Benzyl alcohol

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

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

Manual Removal

Pediculicide Resistance

Environmental Interventions

Management on the Day of Diagnosis