Lice are the crawling insects; nits are the eggs they glue to hair close to the scalp, and knowing which one you are looking at decides what happens next. The CDC says finding a live nymph or adult louse on the scalp or hair is the best way to diagnose head lice. Eggs on their own can be old. What you do next depends on which one you see, and how far it sits from the scalp.
Lice, Nits and Nymphs: One Insect, Three Stages
Those three words describe the same insect at different ages. Head lice are parasitic insects that usually live on the scalp and feed on small amounts of blood from it. The CDC puts an adult louse at roughly 2 to 3 mm long, about the size of a sesame seed, and says an adult female can lay about six eggs each day. Those eggs are the nits. They take about a week to hatch into nymphs, which look like adult lice but are about the size of a pinhead and need about seven days to mature. An adult louse can live on a person’s head for about 30 days.
Is That Speck a Nit or Dandruff?
Attachment is the difference. The AAP says nits are firmly attached to hair, while dandruff, dirt or other particles are not. The eggs are oval, 0.8 mm long and 0.3 mm wide, and usually yellow to white. The CDC says misdiagnosis of head lice infestation is common. If you want a closer look before you decide, see what lice eggs look like in a child’s hair.
| What you find | How it behaves | What the CDC says it means |
|---|---|---|
| A live nymph or adult louse | Moves quickly, avoids light | The best way to diagnose head lice |
| Nits within 1/4 inch of the base of the hair shaft | Firmly attached by a sticky substance | Where to look for nits |
| Nits more than 1/4 inch from the scalp | Still stuck to the hair | Almost always hatched or dead; with no nymphs or adults, probably an old infestation that does not need treatment |
Finding nits but no live lice is a specific situation with its own answer.
How the AAP Describes a Head Check
A head check is bright light, wet hair, small sections and a fine-tooth comb. The AAP says to seat your child in a brightly lit room, part the hair, and look for crawling lice and nits one section at a time. The CDC says live lice are hard to spot because they move quickly and avoid light, and that a magnifying lens may help.
- Wet the hair, then comb it in small sections with a fine-tooth louse or nit comb.
- Wipe the comb on a wet paper towel after each pass and examine the scalp, the comb and the towel; it helps to know what lice and nits look like on a comb.
- Start at the hairline at the back of the neck or behind the ears, where the AAP says they are easiest to find.
Why Itching Is a Late Signal
Itching can start weeks after lice arrive, and a person can have no symptoms at all. The CDC says itching is the most common symptom and is caused by an allergic reaction to louse bites, but that it may take four to six weeks for itching to appear the first time a person has head lice. The CDC also lists a tickling feeling in the hair, irritability, sleeplessness, and sores from scratching. It says people may have no symptoms at all, particularly with a first infestation or when an infestation is light. The AAP says itching can last for weeks even after the lice are gone.
Treatment and Retreatment: What the CDC and the AAP Say
Treatment is for an active infestation, and the whole household gets checked. The CDC’s treatment guidance says to check all household members and other close contacts, and to treat everyone who is infested, plus anyone they share a bed with, at the same time. The AAP says the most effective way to treat head lice is with head lice medicine, and to check with your child’s doctor before beginning any head lice treatment.
Whether a second round is needed depends on the medicine. The CDC says some medicines kill lice and eggs, so retreatment is usually not required for those, while others kill lice but not eggs, which means treating again about a week later, 7 to 9 days depending on the drug.
The CDC’s guidance is to use the medicine as directed on the box or label, and not to use a combination shampoo/conditioner, or conditioner, before it. A few lice still moving slowly 8 to 12 hours afterward is not a reason to reapply, because it takes time to kill all the lice. There is no scientific evidence, the CDC says, that suffocating head lice with mayonnaise, olive oil or similar substances works.
After each treatment, the CDC and the AAP both describe combing out nits and lice every 2 to 3 days for the next 2 to 3 weeks; removing dead lice and nits from hair is part of that stretch. Extra household measures are usually not necessary, the CDC says, but it does list a few:
- Machine wash and dry clothing, towels and bed linens used in the two days before treatment, with hot water at 130 degrees Fahrenheit and high heat drying.
- Seal anything you cannot wash or dry clean in a plastic bag for two weeks.
- Soak combs and brushes in hot water, at least 130 degrees Fahrenheit, for 5 to 10 minutes.
- Skip fumigant sprays and fogs, which the CDC says are not necessary and can be toxic if inhaled or absorbed through the skin.
Frequently Asked Questions
Can head lice jump or fly?
No. The CDC says head lice move by crawling and cannot hop or fly. The AAP says the main way they spread is close, prolonged head-to-head contact, and that there is a very small chance of spread by sharing combs, brushes, hats and sports helmets.
Does finding nits after treatment mean it failed?
Not by itself. The CDC says nits may stay in hair after treatment, but that successful treatment will kill crawling lice. It lists misdiagnosis, conditioner applied before the medicine, instructions not followed, resistance and reinfestation among the reasons a treatment fails, and says a provider may suggest a different medicine.
Can my child catch lice at the pool?
Swimming is not the worry. The CDC says chlorine levels in pool water do not kill head lice, and that lice can survive under water for several hours but are unlikely to spread in a swimming pool. MedlinePlus points instead to shared headphones, hair ties and helmets.
Can we get head lice from the dog or cat?
No. The CDC says animals do not get or spread head lice, and that head lice feed on human blood. On the treatment side, the AAP says never to use medicines made for use on animals, and never to use gasoline or kerosene.
Does getting lice mean our home is not clean?
No. The CDC says getting head lice is not related to cleanliness of you or your environment, and MedlinePlus says personal hygiene and cleanliness have nothing to do with it. The AAP says lice attach to anyone’s hair, clean or dirty, and that anyone can get head lice.
How Lice Lifters of Mercer County Can Help
When you would rather not be the one squinting at a hair shaft, that is a reasonable place to stop. At Lice Lifters of Mercer County we check the whole family, which is the part that is hardest to do well yourself at the end of a long day. Our professional lice treatment is non-toxic and done in one visit, and we hold same-day appointments for families who found something this morning. Our 30 Day Guarantee applies when the whole family is checked. If you are unsure what you are looking at, you can book a head check and hand the comb, the light and the small sections to someone else.
