“Dr. Roy, you’ve got to help me!”

The most heartfelt pleas I ever hear from parents are for three things:

• The three year old who won’t use the potty—so can’t register for school.
• The 15 month old who still isn’t sleeping through the night.
• The school-aged girl(s) with recurrent lice.

Parents hate the idea that their child has lice. They’re icky, they’re crawly, and even talking about them makes everyone in the room start scratching. But parents and schools need to keep this in perspective. Head lice do not transmit any human disease. They have nothing to do with poor parenting or unsanitary living conditions. In many parts of the world, lice are essentially considered normal things that normally live on just about everyone’s head.

Still. They ick me out, too.  So let’s figure out the best way to kill them, for good!

The enemy is the human head louse (multiple: lice, singular: louse), a creature about 3 mm long with six splindly legs that scoots around and between human hairs, right close to the scalp. Lice feed by sucking up tiny amounts of blood every few hours. The itching is part of an inflammatory reaction to the saliva deposited when a louse bites. Adult lice live for about three weeks, and females can lay about 10 eggs a day. Eggs are “glued” to hairs very close to the scalp, hatching about 7-12 days later (quicker in warmer climates.) Only eggs in the warmth found about ½” from a head are likely to hatch.

After an egg hatches, the egg casing remains glued to the hair shaft, moving further out as the hair grows. These little nubs, still glued firmly to a single hair, look a lot like a sesame seed. They can be pulled off with effort or with a nit comb—though in fact there’s no important reason to pull a nit off. If it’s more than ½ an inch from the scalp, it has either hatched or it’s dead. “No-nit” policies at schools are ill-advised, as even children well-treated for lice who are in no way contagious still have nits.

Transmission of lice from child to child occurs almost exclusively from head-to-head contact. Lice are far more common in girls because they spend more time playing with their heads together, and their longer hair probably helps sweep lice from head to head. Transmission on brushes, combs, hats, and other hair accessories is probably very rare—healthy, egg-laying lice do not readily leave their warm host. Lice found on floors, beds, combs, and other household surfaces are already dead or dying.

Lice are best diagnosed by a trained person finding live lice running around the scalp. Sometimes, running a lice comb through the hair and then examining the comb can also reveal the critters. For the examination, some people wet the hair with water, oil, or hair conditioner to slow down the lice, making them easier to spot. Lice can also be diagnosed by spotting egg casings less than ½ inch from the scalp, glued on to hair shafts. The best place to look for these is in the nape of the neck and behind the ears. In several studies, laymen and school nurses were unable to tell lice eggs from specks of dirt, dandruff, and flakes of skin—so a diagnosis made without actually spotting live lice is always suspect.

Treatment efforts should focus on the head of the affected children. There’s really no evidence that aggressive treatment of the household, bedding, couches, and other items  makes any difference. Most cases of failed treatment for lice occur because the treatment wasn’t applied correctly, or the child resumed playing with another infested child and was re-exposed.

First-line treatment for lice should start with permethrin 1%, marketed over-the-counter as the brand Nix in crème rinse form. It has very low potential toxicity to mammals, and is very effective when used correctly. A unique bonus: Nix leaves some residual anti-lice power behind, as long as a conditioning shampoo hasn’t been used. To use Nix, first wash the hair with an ordinary shampoo, and towel dry. Then apply, massage in, leave on for 10 minutes, and rinse with water. It’s a good idea to repeat the treatment in 7-10 days. Some experts feel repeating the treatment in 9 days is ideal; others recommend repeating the treatment twice, each a week apart. The idea behind repeat treatments is to kill any freshly-hatched, juvenile lice before they can mature and breed. No lice treatment is 100% effective at killing eggs.

There are several other over-the-counter (OTC) lice killers. Many contain pyrethrins, including Rid, A-200, R & C, Pronto, and Clear Lice System. These are compounds extracted from chrysanthemums. They’re very safe for human use, but probably not as effective as the ingredient in Nix. LiceMD contains no lice toxins at all, but claims to kill by suffocation. Many home remedies, including mayonnaise and other gooey liquids, might work the same way, but they can be difficult to remove. The limited published evidence shows that home and herbal remedies are less effective than Nix.

Two widely-used prescription products are FDA-approved for lice. Ovide contains malathion, a potent insecticide. It has a high alcohol content, creating a risk from fire—which is not recommended as a lice-removal strategy. Ovide is applied to dry hair, then left on for 8-12 hours before rinsing. The newest prescription for lice is Ulesfia, a non-toxic product that kills by suffocation. It is applied for only ten minutes, but can be quite expensive because several bottles are needed to thoroughly treat longer hair. These is no evidence that any prescription product is generally more effective than OTC lice preparations.

The most important step in using any lice treatment is to read and follow the directions carefully. Most treatment failures are either caused by a mis-diagnosis (that is, the child doesn’t really have an active lice infestation) or incorrect use of the lice treatment. It’s also important to follow the instructions for re-treatment 7-10 days later to ensure that freshly hatched juvenile lice are killed off, permanently interrupting the cycle of egg-laying.

Removal of nits and egg casings is not necessary after lice treatment. Only live lice can be transmitted and only live, mature lice can lay more eggs. Still, many families want to remove nits for aesthetic reasons and to avoid future calls from the school nurse. Nits can be picked off by hand, one-by-one, or combed out with patience and a fine-toothed (preferably metal) nit comb. Some people find that the glue holding the lice in place can be loosened by a spray of diluted vinegar.

All household members of a child with lice should be checked for lice, and treated if live lice are found or any egg casings are found on hairs less than ½” from the scalp. It’s also a good idea to treat children who share a bed with a child with lice. Many families decide to treat everyone in the household, and as long as the treatment is safe that’s a reasonable thing to do. It’s a good idea to clean bedding and hair-care items of the person with lice, but martyr-like efforts to super-vacuum and sanitize every item in the house are unnecessary.

After successful treatment, scalps remain itchy for up to a week. OTC anti-itch shampoos can help, as can treatment of limited areas of itchy scalp with OTC hydrocortisone cream. Oral Benadryl can help if the itching interferes with sleep.

Just about every mammalian species has their own variety of lice, and there’s no good way to completely avoid them. Fortunately, they don’t actually make anyone sick. Remember: there are effective, safe strategies to get rid of lice without shaving your child’s head– or pulling out your own hair!

Roy Benaroch is a pediatrician who blogs at The Pediatric Insider. He is also the author of Solving Health and Behavioral Problems from Birth through Preschool: A Parent’s Guide and A Guide to Getting the Best Health Care for Your Child.