How Head Lice Is Diagnosed

Head lice are a common problem among school-age children and are diagnosed by spotting the live lice or their eggs, called nits, on the scalp or hair. You can learn how to recognize the lice and nits so you can screen your child and other family members. A special comb is often helpful in this process. The good news is that no known diseases are carried by common head lice. The bad news is that they can make you itch and can easily spread between children and their family members.

head lice diagnosis
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Self-Checks/At-Home Screening

The most common sites for lice are around and behind the ears and at the neckline on the back of the head. They can also appear on the eyelashes or eyebrows. Live head lice grow to be about the size of a grain of rice and are dark-colored. They will run from the light, so it's not that easy to see them.

To find live head lice, separate the hair all the way down to the scalp and look for movement. It is best to use a magnifying lens and a fine-toothed comb. If the lice are alive and moving, the infestation needs to be treated to prevent spreading to other people.

Nits are the eggs lice lay on the hair shaft and they are firmly attached with a cement-like substance. They may be shaped like a teardrop. They are 0.8 millimeters by 0.3 millimeters in size, which the CDC describes as being the size of a knot in a thread. They are yellow to white, but may sometimes be the same color as the hair.

Nits are like lice—it's the warmth of the scalp that keeps them alive. Finding nits isn't enough to determine if there's a current infestation. You only need to be concerned with nits that are within a quarter inch of the base of the hair shaft. Those that are farther from the scalp are likely to have already hatched or be non-viable, but they can remain attached for months. If nits haven't hatched by the time hair grows more than half an inch, they probably won't hatch at all.

Once an active infestation is treated, self-checks must continue to ensure the full removal of nits.

Labs and Tests

If you are unsure about whether or not you have found lice, set up an appointment with your family physician. A healthcare provider is likely to be familiar with the appearance and can take a look for both lice and nits, as well as lice feces. If unsure, the healthcare provider may place a piece of transparent tape over the suspected nits or lice in an effort to collect a sample that can be looked at under a microscope.

Your practitioner may use a Woods lamp to help search for nits. This lamp emits ultraviolet light and is also commonly used by dermatologists to look for bacterial and fungal infections, porphyria, and vitiligo.

The healthcare provider will set up a dark room, turn on the lamp, and hold it about four to five inches from the scalp. The skin and hair do not normally shine under ultraviolet light, but a variety of skin infections and infestations will glow, including lice nits.

To prepare for the test, it's best not to use any hair products, as some may have ingredients that also glow under the lamp. You should not look directly into the light since it can damage your eyes.

Head Lice Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Child

Differential Diagnoses

It is easy to confuse dandruff with nits. Dandruff differs from nits in a few ways:

  • Size: Dandruff particles are various sizes. Nits are fairly uniform in size.
  • Location: Dandruff flakes can be all over the head. Nits tend to be more concentrated in areas where head lice like to live (the base of the neck, behind the ears).
  • Staying power: While you may be brushing flakes of dandruff from your shoulders, nits don't fall off. Sometimes they are so stuck that you literally have to pull them off the hair with your fingernail during removal.

Hair casts, which are the remnants of the root of the hair follicle, may also be confused with nits. However, these move freely up and down and the hair shaft. You may also confuse hairspray, gel, and other hair product residue with nits. Some people may also have a psychological condition that leaves them convinced they have bugs crawling on them while they don't have any signs of lice.

Even when lice has been confirmed, you need to differentiate between an active infestation and leftover nits. Nits only tell you that head lice used to be there. They don't tell you if head lice are present now. The American Academy of Pediatrics notes that you should only treat active infestations.

Frequently Asked Questions

  • How can I check myself for head lice?

    You can examine your own scalp for lice in the same way you would check someone else's. Get your hair wet and run a fine-toothed comb or a nit comb through one section of hair from the scalp to the ends, then check the comb under a magnifying glass for lice or nits. Repeat until you've combed through all of your hair, and then repeat.

  • How should I clean my home after a lice diagnosis?

    Lice can't live longer than a couple of days once they fall off the scalp, so a few simple housekeeping measures should prevent a re-infestation:

    • Launder bedding, towels, and clothing used or worn within 48 hours before treatment for lice. Use hot water to wash and the hot setting to dry.
    • Dry clean clothing and other items that can't go into the washing machine.
    • Vacuum carpets, rugs, and upholstered furniture; if you have a child who uses a car seat, vacuum that, as well.
    • Put items such as pillows that can't be laundered into plastic bags and seal them for two weeks.
  • Are head lice caused by poor hygiene?

    Absolutely not. They are merely parasitic pests that spread easily from one person's scalp to another and have nothing to do with being dirty or sick. Nor do they cause any long-term problems as long as they're properly treated.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  11. UpToDate. Patient education: Head lice (Beyond the Basics).

Additional Reading

By Rod Brouhard, EMT-P
Rod Brouhard is an emergency medical technician paramedic (EMT-P), journalist, educator, and advocate for emergency medical service providers and patients.