Getting Nit-Picky About Head Lice Control
 

BIOLOGY AND LIFE CYCLE

All lice are wingless insects that go through simple metamorphosis (egg, nymph, adult).  Lice do not have jumping legs like fleas and cannot jump from host to host.  They have specialized claws for clinging onto hair.  Some lice feed by sucking (head lice) and some by chewing.  Sucking lice are blood feeders and have a narrow head with piercing-sucking mouthparts, and must have a living host on which to feed and reproduce.  These kinds of lice are host specific and rarely survive more than 48 hours away from their host.  Head lice, Pediculus humanus capitis (order Phthiraptera) prefer to live and feed on the human head and are the most common human-infesting species in the U.S. Adults are 2-3.5 mm long.

There can be 10 to 12 overlapping generations per year, depending on the temperature and access to blood meals.  A mated female can lay about 5 to 10 eggs (or nits) per day for 4 to 5 weeks. Individual eggs are glued onto hair shafts close to the scalp.   Eggs hatch into nymphs after incubating for 10 to 14 days and begin feeding immediately. Nymphs go through 3 instars before becoming adults in 10 to 12 days.

MEDICAL IMPORTANCE

Head lice feed on blood from the scalp several times a day.  While feeding, the lice inject saliva that can cause the skin to become itchy and irritated.   A newly infested person may not develop an irritation for 4-6 weeks, because it takes time to become sensitive to the saliva.  Constantly scratching the scalp can lead to secondary infections.  A scabby crust may form from long term lice exposure, and in some cases the skin can become thickened and discolored.   Head lice will rarely, if ever, transmit diseases to humans.

INSPECTION

Periodically checking for head lice can prevent advanced infestations.  This is especially true if you or a family member is in close contact with others on a regular basis.   Shampoo hair without a conditioner, and comb.  Divide hair into sections and look for eggs and adults.   Head lice are most commonly found within 0.5 inch of the scalp.   If any lice are found, it is important to check all family members.

CONTROL

Launder clothes and bedding on the highest heat settings or have them dry-cleaned.  Non-washable items should be sequestered in plastic zip top bags for 2 weeks or frozen for 2 days (a good option for earphones).  Vacuum, sweep, and dust to remove shed hair with eggs attached.

Medicated shampoos are the most common treatment for head lice infestations.  Products containing permethrin (Nix) or pyrethrins with piperonyl butoxide (A200, Rid, Pronto Plus) are usually effective.  Prescription products, like Ovide, are also available.  Multiple applications are often necessary to kill eggs and nymphs.

Non-medicated shampoos, like TLC Lice shampoo or Lice Killer shampoo, are also available, and safe on sensitive skin.  They should be used where strains of head lice have become resistant to conventional medicated shampoos.  They must be used every day for 2 weeks, along with blow drying and brushing to destroy all life stages.  Alternatively, wash hair every 3 days for 3 weeks with a gentle cleanser, like Cetaphil, and blow dry with hot air for 20 minutes.  Because no lice shampoo is 100% effective, the use of “nit combs” is highly recommended.  Fine-toothed combs, such as LiceMeister should be used every other day for 2 weeks.  Continuously dip the comb in hot, soapy water as it is worked through each section of hair.

Head lice can be an embarrassing problem for you and your family.  Unfortunately, pediculosis is often stereotyped with dirty people.  The truth about lice is that they are a nuisance, but can be controlled with thorough inspection and sanitation.  For more information, see the Human Lice Fact Sheet.

-Erin Hodgson, Extension Entomologist