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Harvard Commentaries
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Medical Myths Medical Myths

Yikes, Lice!

October 23, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

I have to admit it. For the longest time, I bought into the myth that an infection with head lice was a clear sign of poor personal hygiene. I learned – or maybe I assumed – it was a problem limited to kids living in filthy and crowded conditions. Wrong!

Fact Versus Fiction

Misconceptions about head lice are common. Here are some facts about lice infections that may surprise you.

  1. Lice have been around for centuries. In fact, archeologists have discovered mummies with lice!
  2. They are found in all geographic areas throughout the United States and among all economic groups.
  3. Lice are not commonly spread by sharing combs, brushes or hats. Most spread is due to direct contact with infected hair among younger children who wrestle, hug or otherwise have close contact.
  4. An infection caused by lice is not a serious illness. It may itch, but it usually causes no symptoms. The emotional toll is probably its biggest impact, as nobody likes to think of a blood-sucking insect infesting their hair.
  5. Shaving a child's head is not the best way to treat lice. Although it works, it's rarely (if ever) necessary. And, of course, there is a cost — just ask your child how they feel about going bald for a while.

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Lice 101

The official name of head lice is Pediculus humanus capitis. Sometimes an infestation of head lice is called pediculosis. The lifespan of a single louse is just a few weeks. The female lays up to 100 eggs or "nits" at a time. She secretes a "glue" that attaches the nits onto strands of hair near the scalp. Eight days later, the eggs hatch. Within two weeks, they are adult size and, in their remaining days or weeks of life, they feed once or twice a day on human blood. Their six legs allow them to grab onto hairs and move from one to the next. They can move quickly, which makes them hard to see.

Although these parasitic insects like human blood, they are not crazy about dogs, cats or other pets. So let's expose another myth about lice: They spread from pets to kids. In fact, lice do not infect our pets. And, they can't live for more than a day or two without a meal of human blood. So extensive vacuuming, cleaning furniture and scrubbing floors may do little to prevent the spread of lice because they are not likely to be on these surfaces. (If they are, they're probably dead.)

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What Can You Do About Lice?

If you or your child becomes infected with head lice, don't panic. It may seem just awful, but it's not dangerous. Nor is it a reflection of your cleanliness or any other character flaw. And, by all means, do not go online or to medical textbooks to look at pictures of the parasite — it will only make things worse! (If you can't resist, however, check this out!)

Finding a live, crawling louse is important because it clinches the diagnosis. Only active, living lice should be treated. Don't take the advice of friends, family or strangers to shave your head, or to coat it in petroleum jelly, olive oil or other thick substances intended to suffocate the parasite. Shaving your head will work but it's rarely necessary. And suffocating head lice will probably prove harder than you thought. They are hardy and, rather than curing the infection, it's more likely you'll still have lice imbedded in your now greasy hair.

Instead, stick with the treatments that have been tested and proven to be effective. Common treatments include medications that contain pyrethrin (an extract of chrysanthemum), permethrin (the synthetic form), malathion, lindane, benzyl alcohol lotion and spinosad. Usually a second treatment in 7 to 10 days is recommended. Occasionally, lice are resistant, which may be increasing. In these cases, ivermectin may be recommended, but check with your doctor. Careful combing to eliminate nits from the hair can be helpful but is most useful for kids with short, straight hair.

While "industrial cleaning" of your furniture and carpets is not necessary, it's probably a good idea to wash sheets, pillowcases or clothing (using hot water and a heated dryer) that have come into contact with an infected person's head. Brushes, combs, hair accessories and hats should be washed in hot water each day until the infection is gone.

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Why Do Myths Persist?

One reason for these myths is that there is more than one type of lice. Body lice (official name: Pediculus humanus corporis) are more common in settings where people wear several layers of clothing and do not wash them regularly. For example, body lice are more common during war, after natural disasters, in poorly run nursing homes and among the poor and the homeless. Unlike head lice, body lice can spread serious illness, including typhus, trench fever and louse-borne relapsing fever. In the last few centuries alone, millions have died of these diseases. Perhaps it's those "other lice" — pubic lice, or "crabs" — that have people worried about head lice. They are similar to head lice except for their location and the fact that they are usually transmitted sexually.

But, mostly, I think it's the "gross out" factors of having a scalp and hair infection, and the spread of erroneous information passed from one generation to the next that has kept the myths alive.

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The Bottom Line

When it comes to lice, the spread of misinformation may be more of a problem than spread of the disease! If you or someone you know has head lice, talk to your doctor or your child's pediatrician about what to do. But, there's no need to pull you hair out over it. (Sorry, I couldn't resist.) It's an annoying but not serious condition. There is this one consolation about having head lice: It's likely you'll have plenty of company.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.


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