Head Lice

Head Lice

What do we know?

Head lice are tiny parasites.  Their formal name is Pediculus humanus capitis.

Their perfect living conditions are at the base of the hair shaft on the head, eyebrows and eyelashes of humans.  From there, a louse feeds on blood from the scalp several times a day.

This location also provides an ideal temperature for eggs, or nits, to incubate.  A nit hatches into a nymph after about a week.  The nymph grows into an adult louse in another 9-10 days.  Adult lice then live for 3-4 weeks.

Nits can be hard to remove because the female louse attaches the nit to the hair with a sticky substance, about 4-5 mm from the base of the shaft.

How common are head lice?

The simple answer is, very common.  One study done in Atlanta screened 1729 school children for head lice.  1.6% had lice, and 3.6% had nits without lice.  The good news is that, of those with nits, only 18% converted into lice.

Overall, however, this adds up to more than 6 million school children a year in the USA.  That suggests about 700,000 Canadian school children are infected each year.

Who gets lice, and how do they get it?

Lice are most common in three groups:

  1. Pre-school children attending daycare.
  2. School age children up to 11 years old.
  3. Family members living in the same house as someone with lice.

Other important facts:

  • Lice pass from child to child by direct head-to-head contact.  They do not jump or fly.
  • Infection is not caused by poor hygiene or an unclean home or school environment.
  • Children can still swim.  Lice cling tightly to the hair and it is very unusual for them to pass in the water.
  • Lice are not spread from pets, including dogs and cats.
  • Occasionally, they can be passed by clothing, bedding and linens, although this is not as common.

What are the symptoms of lice?

Itchiness is the most common symptom at all ages.

  • Itchiness occurs behind the ears and at the base of the neck as well as on the scalp.
  • Some children also experience poor sleep, because head lice are most active in the dark.
  • A tickling feeling on the scalp may occur as well, as the lice move about.

Are there any complications of head lice?

A louse does not pass infections along.  They are annoying, but they are not a medical or public health hazard.

Scratching can cause secondary infection if the scratching breaks the skin and allows bacteria under the skin.

How are head lice diagnosed?

Diagnosis occurs when nits are found on the hair shaft, usually about 5 mm from the scalp.

Adult lice are very active, and avoid light.  Some suggest dampening the hair before inspecting, to slow the adults down and make them easier to see.

Use a bright light and a fine comb.  Most often, the diagnosis is made by finding the nits.

How are lice treated?

Lice are treated with one percent permethrin lotion massaged into the hair, after removing nits with a comb.  Permethrin needs to be reapplied a second time, 7-10 days after the first treatment.

Because treatment products can be toxic, it is very important to follow directions on the package exactly.  More detailed treatment guidelines can be found here.

If you have any concerns about diagnosis or treatment, you should see your doctor or nurse practitioner.

Can children with lice continue to attend school?

Yes! Head lice do not transmit infection, and effective treatment is available.

Healthy children with head lice should not be excluded from school, and do not need to be nit-free to attend school.

Head lice are certainly inconvenient, but as we’ve learned more about lice in recent years, no-nit policies are no longer needed.

– Dr G Paul Dempsey

Photo credit: Howard County Library System


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