Tony Kiszewski and Richard Pollack of the Harvard School of Public Health answered a few questions for nationalgeographic.com.

ARE HEAD LICE FOUND PRETTY MUCH WHEREVER PEOPLE LIVE? ARE THERE ANY GEOGRAPHIC PATTERNS?

They are found far and wide; in every possible climatic or environmental situation from deserts to cities to rain forests. In the United States we get reports from virtually every state. Anecdotally we hear of higher infestations in warmer areas, but we don’t have any hard data to support this.

WHY DO LICE PROVOKE SUCH A REACTION IN PEOPLE? DO THEY POSE ANY HEALTH THREAT?

Insects provoke anxiety in many people. Some people are absolutely horrified when a moth invades their home or when an ant walks across their picnic table. Can you imagine how these people react when an insect invades their bodies? With some people, just talking about lice is enough to make them scratch and squirm. Some think that they are infested despite intensive examinations that reveal nothing.

There appears to be a primal fear associated with insects that relates perhaps to their alienness. We can’t say it’s because they’re not warm-blooded, fuzzy creatures like us, because that doesn’t explain why people react so badly to mice. This seems to be a cultural phenomenon. People from certain cultures, such as the Yanomami of Venezuela, actually consider louse infestations to be normal. Head lice and their eggs (nits) generally pose little direct health threat in the United States. Mild itching from the bites is the most frequent consequence. Greater harm may come from indirect effects: Overzealous insecticidal use may cause toxic reactions in patients.

WHAT ARE THE CHALLENGES INVOLVED IN GETTING PARENTS, SCHOOLS, AND COMMUNITIES TO STOP SEEING LICE AS A ’MORAL’ OR ’NEGLECT’ ISSUE?

One problem is the presumed association between head lice infestations and hygiene. There is no association. Hygiene has very little to do with the probability of acquiring infestations. The neglect issue comes from the perception that all louse infestations are readily treatable and that parents whose children have lice are not providing proper care.

It has been our experience that children who have been misdiagnosed or have insecticide-tolerant lice are being overtreated. It’s not the parents’ fault much of the time. Sometimes the only recourse is daily combing and nit-picking, and this may take some time to eliminate an infestation.

Another barrier is the lack of understanding about the modest communicability of these infestations. Having an infested child in a classroom does not necessarily mean that any of his or her classmates are destined to become infested. People seem to think that these things will crawl or even jump from one person to another and will lie in wait on stuffed animals or sofas for their victims to appear. It actually takes fairly close physical contact for transmission to occur—touching heads or perhaps sharing pillows, combs, or hats. Lice generally survive for less than a day away from a human host.

Another problem is knowing when an infestation is real. Many people have debris or dandruff that adheres to their hair shafts and can be mistaken for nits. Others despair at their inability to clear nits from their children when, in fact, the nits are but empty husks from a prior infestation.

HOW CAN SCHOOLS AVOID EXTREME REACTIONS WHILE STILL PROTECTING STUDENTS? WHAT SORT OF MESSAGE SHOULD SCHOOLS SEND HOME?

This is a difficult one. How do you manage a communal phobia? Schools should do only what is necessary to remove the risk of transmission to other children. Anything more, such as excluding from school children with dead nits in their hair, is catering to hysteria.

Perhaps some sort of presentation to parents on the biology and transmission of lice would help let them know that lice are not superbugs. You will never be able to convince everybody, though. Some parents won’t be happy with such a policy, but policies should be formed around reality, not illusion.

WHAT WOULD BE AN APPROPRIATE COMMUNITY RESPONSE TO AN OUTBREAK OF LICE?

Lice and their eggs should be examined by a competent person to confirm that an active infestation exists. The presence of old (dead or hatched) eggs should not be cause for treatment or exclusion from school. On the other hand, actively infested children should be sent home where lice and eggs can be removed manually. Parents may choose to augment (but not replace) manual louse removal with over-the-counter pediculicides. Children who have been treated pose little risk to others, and may return to school.

A single follow-up treatment about two weeks later should be conducted to target any newly hatched nits. Only those children with active lice in their hair after one or both of these treatments should be considered infested.

Active lice that are found after such treatments may suggest the presence of insecticide resistance.

It is not necessary to treat other family members unless they too have lice. Likewise no intensive campaigns of household cleaning are necessary.

The Harvard School of Public Health has more information about human lice and treatment options at http://www.hsph.harvard.edu/headlice.html.