Update on Head Lice for Medical Providers

This article originally appeared in the Disease Control Newsletter Volume 26, Number 3; April 1999

Head lice (Pediculus humanus capitis) infestations are a major public concern in Minnesota and across the United States. While head lice are not known to be vectors of disease, the public looks to medical providers and public health workers for effective treatment options against these small insects. Currently, significant public health resources at state and local levels are used to address this problem.

Head lice are obligate parasites of humans that are found primarily on the scalp (especially occipital and postauricular areas). The adult female louse lives 3-5 weeks and lays between 5-10 eggs (nits) per day. Nits are attached near the bases of hair shafts, and most viable nits will be found within 1/4 inch of the scalp. Nymphal head lice emerge from the nits after 6-10 days and feed daily on human blood. After about 10 days (and three molts) the nymphs become sexually mature adult head lice.

Head lice are transmitted primarily through direct head to head contact between people (especially children). Transmission from fomites occurs but is thought to be less important. Shared objects such as combs, brushes, hats, towels, and bedding have been suspected in many infestations. However, most head lice die of starvation or desiccation within two days off of the host.

Several over-the-counter head lice treatment options are available. Products containing permethrin and pyrethrin are the current treatments of choice. Both have been shown to be effective against head lice. However in recent years there has been widespread suspicion that head lice may have increasing levels of resistance to these materials. This apparent resistance has not been well studied or documented yet. Many providers prescribe Lindane for patients with chronic infestations of head lice. While these treatments are often effective, Lindane is more toxic to humans, and some populations of head lice have been shown to be resistant to this pesticide.

Many alternatives to the over-the-counter or prescription head lice treatments have become more popular in recent years. Some of the more widely used products include petroleum jelly (Vaseline), mayonnaise, and various oils (e.g., olive, vegetable). In theory, when applied to the hair and scalp, these treatments either suffocate or create a habitat unfavorable to the head lice. While there is anecdotal evidence that many of these treatments may work, there are little if any carefully collected efficacy data for most of these products.

Mechanical removal of live lice and potentially viable nits (those within 1/4 inch of the scalp) is an important supplement to all head lice treatments. None of the treatments are 100% effective against live lice and are even less efficacious on the nits. Many of the permethrin and pyrethrin head lice treatments recommend a follow up treatment 7-10 days after the first treatment to eliminate freshly hatched head lice nymphs, and lice that survived the initial treatment. Regular grooming with a louse comb or finger nails will remove many of these lice and potentially viable nits. These regular checks also help the patient monitor the status of their infestation. If remaining nits are greater than ½ inch out on the hair shafts, and no live lice have been seen for two weeks, the infestation is likely gone. As overuse of the over-the-counter products appears to be a common practice, these checks will help to reduce unnecessary treatments.

Many apparent chronic infestations of head lice are actually reinfestations. If the infestation returns after being gone for two or more weeks, the patient has probably been reinfested. Children are often exposed to the same child that gave them their infestation initially. While reducing transmission is difficult, parents should be encouraged to speak with their children about reducing direct head-to-head contact with other children, and avoiding shared objects such as brushes and combs. Parents should also be encouraged to communicate with the parents of children that may have been exposed to their infested child.

This was originally printed as part of the Minnesota Department of Health Disease Control Newsletter, Jan-Apr 1999

Updated Tuesday, November 16, 2010 at 12:21PM