Everything You Ever Wanted to Know About Head Lice

Contemporary ClinicOctober 2016
Volume 2
Issue 5

Head lice are 6-legged insects about the size of a sesame seed that cling to the scalp and neck and survive by feeding on human blood.

What Are Head Lice?

They are 6-legged insects about the size of a sesame seed that cling to the scalp and neck and survive by feeding on human blood. Lice that are found on the head are calledpediculus humanus capititis(head louse).

How Are Head Lice Transmitted?

They spread most commonly by close human-to-human contact. Head lice move by crawling; they cannot hop or fly, and they are not transmitted by dogs, cats, or other pets. An infestation of head lice most often affects children as a result of direct transfer from the hair of one child to another.1A head lice infestation is NOT a sign of poor personal hygiene or unclean living environment, and they do not carry bacterial or viral infectious diseases.2

What Are the Symptoms of Head Lice?

Itching on the scalp, neck, and ears is the most common symptom, which is an allergic reaction to louse saliva. Lice may be visible, but they are small, move quickly, and avoid light, so they are difficult to spot. Head lice are about 3 mm long and attach their eggs, also called nits, to the base of the hair shaft. The nits stick to the hair shafts and are tiny and camouflaged to match hair color, so they also can be difficult to see; however, they are easiest to see around the ears and hairline of the neck. Empty nits are easier to spot because they are lighter in color and have moved up further from the scalp.

How Are Head Lice Diagnosed?

The gold standard for diagnosing an active head lice infestation is the identification of a live nymph or adult louse. This is done by examining wet hair with lubrication from conditioner. The hair can be combed with a fine-toothed nit comb from scalp to end of hair, and nits will collect in the comb, which verifies an infestation. In addition, your health care provider can look for nits in your child’s hair and may use a specialized light that causes nits to appear bluish.

How Are Head Lice Treated?

Before considering treatment, it is recommended that you or your child visit your health care provider. Studies have shown that children have been treated for head lice with OTC medication when they do not, in fact, have an active head lice infestation. It is possible to mistake the following for an active infestation: dead or empty nits from a previous head lice infestation, dandruff, residue from hair products, bead of dead hair tissue on hair shaft, scab tissue, dirt or other debris, or other small insects in the hair.2

Your health care provider will likely recommend an OTC medication that kills lice and some of the eggs; however, these medications might not kill recently laid eggs. Therefore, a second treatment is usually recommended 9 days after the first treatment to kill nymphs after they hatch and before they become adult lice.

OTC lice treatments contain pyrethrin, which is a chemical compound extracted from the chrysanthemum flower that is toxic to lice. Wash your child’s hair with shampoo and no conditioner to prepare for treatment. A white vinegar rinse before washing may help dissolve glue that holds the nits to the hair shafts. Be sure to follow package directions that explain how to use the medication and how long to leave it in the hair. OTC medications include permethrin (Nix) or pyrethrin with additives (Rid, A-200 Lice Killing). Caution: do not use these products if your child is allergic to chrysanthemum or ragweed.

A prescription treatment may be recommended if the OTC treatment has failed or if there is known resistance to the OTC medications. The prescription medications include:

  • Benzyl alcohol (Ulesfia), which deprives lice of oxygen and is not indicated for children younger than 6 months;
  • Malathion (Ovide) shampoo for ages 6 and older; and
  • Lindane shampoo, which is not recommended for children, pregnant or breastfeeding women, anyone with a history of seizures, or HIV-infected individuals.

Are There Any Nonmedication Treatments?

If you would prefer not to use a medication for treating a head lice infestation, there are some alternative home treatments to consider. Keep in mind that there is little to no clinical evidence of the effectiveness of these treatments:

  • Combing wet hair with a fine-toothed nit comb may remove lice and some nits. This should be repeated every 3 to 4 days for several weeks.
  • Some small clinical studies have suggested that some natural plant oils may have a toxic effect on lice and eggs. These include tea tree oil, anise oil, ylang ylang oil, and nerolidol (found in many plant oils).
  • Household products such as mayonnaise, olive oil, butter, and petroleum jelly can be used to smother the lice and nits. Apply the product to the hair, cover with a shower cap, and leave on overnight.

How Can I Prevent a Lice Infestation?

Lice do not live past 1 day without feeding from a scalp, and eggs cannot survive if they are not incubated at the temperature near the scalp. So, the chance of lice surviving on household items is small; however, they can survive for a short period on clothing or other personal items. Therefore, wash bedding and clothing in hot water. If your child has a favorite stuffed animal, put it in a hot dryer for 30 minutes. Hang clean garments on separate hooks from other children’s garments, and do not share combs, brushes, hats, and scarves.

Dr. Janet Gilbreath is a licensed and board-certified family nurse practitioner,adjunct faculty member, and visiting professor. She has a broad health care background in convenient care, cardiology, primary care, and quality management.


  1. Parasites: lice. 2013. CDC website. cdc.gov/parasites/lice/. Updated September 24, 2013. Accessed August 9, 2016.
  2. Mayo Clinic Staff. Diseases and conditions: head lice. Mayo Clinic website. mayoclinic.org/diseases-conditions/head-lice/basics/con-20030792. Published June 18, 2014. Accessed August 9, 2016.
  3. Head lice slideshow: what parents should know. Web MD website. webmd.com/children/ss/slideshow-lice-overview. Accessed August 9, 2016.

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