Diagnosing Head Lice


I think my child has head lice. I keep my house clean, but I'm embarrassed and afraid other people will think it's my fault. How can I check without going to the doctor?

Dr. Greene's Answer

Lice have been a nuisance to humans since ancient times. They have thrived almost wherever humans have been in prolonged close contact with each other. One notable exception to this has been in areas where the pesticide DDT is in widespread use. In the United States, for a period of about 30 years, lice outbreaks were uncommon. Since DDT was banned in 1973, the number of cases of lice has risen steadily. Today, there are about 12 million cases per year in the United States alone. Each year, many day care centers, schools, neighborhoods, extended families, and small family units face problems with lice. You are not alone.

Two myths:

Myth: Head lice restrict their activities to unclean houses, unclean heads, and unsavory sorts of folks.
Fact: Having head lice is not a sign of poverty or poor hygiene.

Myth: All heads of hair are equally attractive to lice.
Fact: Lice seem to prefer children to adults, long hair to short hair, and they particularly like the hair of females. Interestingly, lice only rarely afflict African Americans living in North America. The lice in Africa and South America have adapted, however, and cases are common in every group on those continents. Cases of lice are most common in children 3 and 10 years old, but can occur at any age.

Adult lice are six-legged, wingless insects 2-4 mm long. They have translucent grayish-white bodies, and look a bit like a grain of rice with six legs. Their heads have two tiny eyes (too small to be seen without magnification) and two small antennae (usually visible). Six pairs of hooks surround the mouth parts, by which they attach themselves to the skin of the scalp for feeding. The mouth contains two retractable, needle-like tubes that pierce the scalp. Salivary juices are injected into the scalp to prevent blood from clotting, and then the lice feed happily, sucking blood through these same tubes. Their translucent bodies turn reddish brown when engorged with blood. Lice completely depend on the blood extracted from humans for existence, and thus will starve to death after 55 hours without blood.

Adult lice can freely move around a head of hair and travel to another person, clothing, plastic combs or brushes, or upholstered furniture. Adult lice usually live for about a month on a human host. During this time, the females generally lay from three to 10 eggs per day (although some female lice have been known to lay up to 5,000 eggs in their lives when in an environment to their liking).

Lice eggs are called nits. These white, translucent, pinpoint-sized eggs are laid near the base of hair shafts, and move outward as the hair grows (nits found near the tips of long hairs suggest a longstanding infestation). Nits are glued tightly to the side of the hair shafts, and cannot be moved along the shafts or knocked off with fingers. The eggs hatch between ten to fourteen days after they are laid. The empty eggs remain attached to the hair shaft. The newborn larvae must feed on human blood within 24 hours, or they will starve to death. The larvae become sexually mature adult lice within about one week.

During this whole life cycle, larvae and adult lice deposit their feces in the scalp, which eventually causes itching as the person develops an allergic reaction to the lice stool. The hallmark symptom of head lice is itching, but a person may have lice for months before the itching begins. For me, just thinking about lice makes my head itch.

Now, a moment of silence to be grateful that lice can’t fly…

Lice spread from person to person when heads touch. Because they can live independent of a person for up to 55 hours, they are also commonly spread via stuffed animals, hats, headphones, combs, brushes, towels, clothing, car seats, sofa cushions, and bedding.

The best way to diagnose head lice is to inspect the head of anyone who might have been exposed to them using a bright light (full sun or the brightest lights in your home during daylight hours work well). A magnifying glass can make the job easier. Part the hair all the way down to the scalp in very small swaths, looking both for moving insects and nits. The entire head must be inspected to make sure there is no problem. Careful attention should be given to the nape of the neck and around the ears, the most common locations for nits. Even one nit in the hair should be treated. The egg might be empty, or contain a dead larva but — then again, it might not!

Frequently, people find “pseudo-nits” and panic unnecessarily. Bits of hair spray, dead skin scales, or loose debris may be seen on hair shafts. These move with pressure from the fingers — nits do not. Also, live nits glow when exposed to a black light (we use black lights in pediatric offices for inspection) and dead nits and empty nits do not.

Historically, the main method for getting rid of lice has been mechanical — physically removing the nits, or “nit picking,” such as apes do for each other during their daily grooming routine. About 30 years ago, powerful pesticides were introduced as lice treatments. For a time, they made treating lice much easier. Over the last several years, however, the lice have become increasingly resistant to these medicines. The resistance is growing. Now, once again, mechanical nit removal is the cornerstone of lice treatment, although the medicines can still be a real help.

Treatment for head lice can be effective, but it is not simple, easy, or inexpensive. A key to success is making sure that ALL individuals who may be potentially affected by the outbreak complete a radical eradication. If 99.99% of the lice are killed, but .01% are not, you already have the makings of another outbreak!

So, you can check easily for lice without going to the doctor, but you do not need to feel embarrassed or ashamed. Your doctor will understand and I do too — from personal experience.

Last medical review on: April 06, 2009
About the Author
Photo of Alan Greene MD
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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