Delousing Head Lice

By Ashli Collins, M.D.

For anyone with a preschool through high school aged child, you have certainly received the dreaded “head lice identified in a classmate” letter.  This letter usually instills fear and parents start digging thru their children’s hair immediately.  This article will hopefully help you understand head lice, its lifecycle, the symptoms it can cause and its treatment.  I will also hope to dispel a few common myths that continue to be heard.


Just to raise the anxiety a little more, head lice causes6 to 12million infestations each year.  It is extremely common, especially in kids ages 3-12 and thankfully does not spread disease or pose a health hazard.  It also is NOT a sign of uncleanliness, but just an outcome from sharing a hat, comb, pillow or close acquaintance with someone who has an infestation.


The tiny louse grows to a length of 2-3mm and usually appears like a grey or brown sesame seed.  The female lives only 3-4 weeks but in that time lays between 5-10 eggs, or nits a day.  These eggs are essentially glued to the hair shaft near the scalp.  The most common place to visualize the nits is behind the ears and at the neckline as temperature and humidity are more suitable there.  The eggs hatch around 10-14 days later and leave behind a white casing on the hair shaft.  The nymphs then grow for 9-12 days, mate and then the females begin laying eggs.  If the hair is not treated, this cycle will then restart every 3 weeks.


The louse lives by injecting small amounts of saliva and taking small amounts of blood from the scalp of its human host every few hours.  Many believe that it is the saliva that causes the intense itching commonly seen with an infestation of head lice.  A louse cannot live off of its human host for more than 24-36 hours as it needs human blood to survive.  It also does not jump, fly, parachute or hop to get to another host; the louse does not have wings and has legs only built to grasp hairs.  Head lice does not live on pets, it requires a human host.


Head lice are spread by close contact with a person with an infestation.  Brushes, combs, hats, pillows, helmets and hair accessories have been theorized to cause spread but actual head to head contact is the most common.  Many children will bring lice home and then share it with the family.


The main symptom with head lice is itching.  Schools/teachers are taught to watch for children who are constantly scratching their head.  Secondary infections from the itching may occur such as impetigo or swollen lymph nodes.


Diagnosing head lice is not always easy.  Retrieving a live louse is the most definitive tool but an adult louse can climb 6 to 30 cm per minute making them hard to catch.  Nits are usually found by the school nurse, pediatrician or parent but these are easily confused with dandruff, hairspray residue and hair casts.  If the presumed nits are not within an inch of the scalp they are less likely lice.  One suggestion to try and find lice is to have the child hold their head over a white towel and brush the child’s hair from the scalp towards the towel to see if any lice are dislodged.


Once lice are identified, treatment needs to take place and notification of the school and other close contacts should be given.  Several over the counter (OTC) and prescription treatments are available.  Rid (pyrethrin) is OTC and is made from chrysanthemums, thus people with an allergy to that should avoid it.  This shampoo is applied to dry hair, let sit for 10 minutes and then rinsed out.  Shampoo treatments should always be performed over a sink with cool water to minimize contact and absorption to the rest of the skin.  Pyrethrins are not 100% effective against lice with 20-30% of the eggs remaining viable after the treatment, thus reapplication in 7-10 days to kill any newly emerged nymphs.


Another common OTC treatment is Nix (permethrin 1%).  It works well and has fewer allergic problems than pyrethrins.  It is applied to shampooed (with non-conditioning shampoo), towel-dried hair.  It is left on for 10 minutes and then rinsed off.  Again, this treatment is not 100% ovicidal and should be repeated in 7-10 days to work against any new nymphs.


Other medicines such as ovide, kwell, elemite are also available but carry more side effects and should be discussed with your health care provider.  Antibiotics, ivermectin and some natural products have also been used with limited scientific studies to back them.  Some parents have asked me about olive oil, mayonnaise and petrolatum (Vaseline or aquaphor) as possible agents to use.  There aren’t any studies to demonstrate effectiveness of these but the residue left behind can be problematic.


Removal of the nits is arguable.  Most schools still want children to be “nit free” although that is not a guideline supported by theAmericanAcademyof Pediatrics.  From a practical standpoint, most feel that removal of nits found within a centimeter of the scalp, after treatment with a pediculicide is appropriate.  This is tedious and time-consuming but often results in a quicker return to school.  It is easiest to remove them while the hair is damp.  Nit combs are available but manual removal by fingernails or tweezers is often more effective.


All household contacts should be checked and those with live lice or nits should be treated.  If another person shares a bed with the infected child, that person should be treated.  It is wise to clean all bedding, brushes, towels, and other personal items in water >120 degrees.  Clothing, furniture, carpets, etc that have been in contact with the infected person in the 24-48 hours before treatment should be cleaned/vacuumed remembering that the louse cannot live away from its human host more than 24-36 hours.  Items which can’t be washed can be placed in a plastic bag for two weeks.


Return to school is based on your school’s policy.  The AAP maintains that after initial treatment, a child may return.  However, many schools remain “nit free” and thus, manual removal of all nits must be done.

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Ashli Colins, MD.  Dr. Collins is a pediatrician with Oldham County Pediatrics, PLLC.  They have offices in LaGrange and in Louisville near the Summit.  Dr. Collins is the mother to twins, Sarah and P.J.  For more information call 502-225-6277 or




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