Sometimes head lice are called nits, even though the word "nits" really means the shells of their eggs.

You might be repulsed at the thought of having head lice, but they are basically harmless and fairly easy to treat. Having head lice is nothing to be ashamed of. It does not mean you don't keep yourself clean. Head lice can't tell the difference between clean hair and dirty hair. They just want to survive, and to do that they need a head to live and breed on.

But since many children are not allowed to go to school if they have head lice, parents need to know how to deal with them quickly if someone in their household gets them.

Many schools have a no-nits policy. School nurses send thousands of children home each year because they think they have spotted nits in their hair. Nits are the shells, or casings, of the head lice eggs, and they get left behind after a head louse hatches. You cannot say for sure that a person has head lice by spotting a nit.

One big problem with head lice is that there are many things said about them that are not proven. In the United States, for example, doctors recommend washing all hats, clothes and bed linens to get rid of them.

 

 

 

 

 

Source:
Centers for Disease Control and Prevention.
Head lice: treatment.
October 2008. Available at http://www.cdc.gov/lice/head/treatment.html (accessed on 22 January 2009).

 

 

 

 

 

² But there isn't any evidence that doing this is helpful.

The truth is that head lice are firmly attached to the hair. They never willingly leave one head unless there is another one nearby to climb onto. The chance of you catching head lice from a pillow or hat is very small. Also, head lice can't live very long once they are separated from a person's head.

See how much you know about head lice by taking our head lice quiz.

To understand how you catch head lice and how to get rid of them, you need to know something about what head lice look like and how they breed.

There are three stages in the life of a louse: the egg, the nymph and the adult louse.

Head lice lay their eggs onto separate strands of your hair. Each female louse lays about five or six eggs a day. The shells of these eggs are called nits. Nits are oval and a bit smaller than a pinhead. The young, unhatched eggs are nearly colorless and blend in with the hair and scalp, making them difficult to see.

These eggshells are hard and extremely tough. They can stay in the hair for months or even years after hatching. To remove a nit, you have to pull it along to the end of the hair. You can't usually just pick them off the hair.

Head lice usually lay eggs near the scalp and stick the eggs to the hair with a kind of glue they make. They place the eggs near the base of the hairs because it is warmer and more

 

 

 

 

 

humidity
Humidity is the amount of moisture in the air. For example, a tropical rainforest has very high humidity, while a desert has very low humidity.

 

 

 

 

 

humid there.

You may find it difficult to spot louse eggs, although once an egg hatches, the shell (or nit) becomes easier to see. It looks white and stays attached to the strand of hair. However, nits are easily confused with other white specks in the hair, especially debris from the hair follicle (the cells that surround the root of the hair), dandruff or even droplets of hairspray.

After seven days, baby head lice (which are known as nymphs) hatch from the louse eggs. Nymphs start to feed on your blood almost immediately. They feed through a tube called a haustellum, which comes out of their head and is used to pierce your skin and burst a blood vessel. You can't usually feel these tiny bites.

Just like all growing insects, head lice need to shed their skin (molt) every few days. The nymph becomes a fully grown louse after it has molted three times. Normally, this takes nine to 10 days. The main differences between nymphs and adult head lice is that nymphs are smaller and they can't mate or lay eggs.

An adult louse can live for up to about 30 days, provided it has a source of food and moisture nearby. To stay alive, the louse needs to feed on human blood every three hours or so. That means it will bite you between four and eight times a day.

If head lice fall out of the hair, they die within about a day. However, they're unlikely to fall out of the hair if they're healthy, because their grip is strong.

Within about a day of becoming adults, male and female head lice will mate, and the female will lay eggs. In her lifetime, a female louse can lay up to 100 eggs, although most head lice don't lay quite so many.

If there is any disturbance to the hair (for example, if it touches someone else's head), the louse will start to crawl outward along the strand of hair. This is when it may make the journey from one head to another.

A fully grown head louse is about the size of a sesame seed. It looks grayish brown, although its color can vary. It is flat and does not have wings.

A head louse has three pairs of legs with powerful claws that it uses to firmly grip the hair. This is why head lice are so difficult to remove. Head lice almost never lose their footing, but they can be dislodged with a very fine-toothed comb.

On its head, the louse has two feelers (antennae). They feel changes in the louse's surroundings. For example, they register the temperature, humidity and chemicals in the air around them.

Head lice spread by crawling from one person's hair to another's. Here's a look at how you can (and can't) catch head lice.

To learn more, take our head lice quiz.

The only sure way to know you have head lice is to find a live louse in your hair. Finding a louse egg or nit (the shell of a louse egg) does not prove that you have head lice.

In one study, out of 50 children found to have louse eggs and nits, only nine went on to get head lice.

 

 

 

 

 

Source:
Williams LK, Reichert A, MacKenzie WR, et al.
Lice, nits, and school policy.
Pediatrics. 2001; 107: 1011-1015.

 

 

 

 

 

⁵ This was because:

It's also very easy to mistake pieces of dandruff or droplets of hairspray for louse eggs and nits. You can also easily mistake debris from the hair follicle (the cells that surround the root of the hair) for nits.

To learn how to spot head lice, see How do I check for head lice?

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