A person will need multiple treatments to eradicate head lice, and this can take around 2–3 weeks.

Head lice are around 2–3 millimeters (mm) long and are often visible to the naked eye. They live on human heads and lay eggs at the bottom of hair shafts. Lice mainly spread through head-to-head contact by crawling from one person’s head to another, as they cannot hop or fly.

Lice are common in children 3–11 years old and more frequent in girls than boys. Head lice are not a sign of poor hygiene or disease — anyone can get them, including adults. These lice do not live on pets.

A child can get lice any time they are playing with other children and have physical contact. Lice can also transmit through sharing items that have contact with the head, such as combs or hats.

The California Department of Public Health states that children are more likely to get lice at family events, sleepovers, or play dates than at school.

This article discusses how long it may take to get rid of lice, the life cycle of lice, and how to treat lice.

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Head lice can take some time to get rid of completely. For example, most treatments for lice only kill live lice and leave the eggs unaffected. This means multiple treatments may be necessary to kill all the lice from the eggs.

Lice eggs take around 1 week to hatch, so most treatment routines will last longer than a week.

The Centers for Disease Control and Prevention (CDC) state that most lice treatments require another treatment 9–10 days after the first treatment.

The CDC also suggests it will be necessary for people to check their hair for 2–3 weeks to ensure there are no more lice or eggs.

Learn more about how to get rid of lice.

The CDC states that adult lice can live up to 30 days on someone’s head, where they feed on blood. However, the lice will die within 2 days away from the head and their blood supply.

Lice follow three main life stages:

  1. Eggs: Head lice eggs or nits are small, yellow-white ovals that attach to the base of the hair. They may appear like dandruff, but a person may identify them more clearly with a magnifying glass. Adult head lice lay eggs that are usually around 0.8 by 0.3 mm and take around 1 week to hatch.
  2. Nymphs: Lice turn from eggs into nymphs. These are gray-white lice that are smaller than adult lice. Nymphs mature into adult lice after around 1 week after they hatch.
  3. Adults: Adult lice are about the size of a sesame seed and are gray-white to tan in color but may appear darker in people with dark hair. Female lice are larger than males and can lay multiple eggs per day.

Learn more about the life cycle of lice.

There are several methods for treating lice. The first step is identifying the issue, for which people commonly use a bright light and fine comb. Identifying lice involves:

  1. Wetting the hair to make the lice easier to see and harder for them to get away.
  2. Sitting under a bright light.
  3. Separating the hair into sections from the scalp and slowly combing outward.
  4. Looking for eggs, nymphs, and adult lice while combing through the hair.

Lice may also cause symptoms that include:

A person should check for lice in household members or other people in close contact with someone who has lice. People can begin treatment after identifying that lice are present.

People with lice typically require over-the-counter (OTC) or prescription medications to kill the lice.

OTC medications may include pyrethrins combined with piperonyl butoxide, which only kill live lice and require multiple treatments to eradicate newly hatched lice. They may also include permethrin lotion 1%, which also only kills live lice without affecting eggs.

Prescription medications require a doctor’s approval and include:

  • benzyl alcohol lotion 5%, which kills live lice but not eggs
  • ivermectin lotion 0.5%, which kills nymphs and adult lice
  • malathion lotion 0.5%, which kills live lice and some eggs
  • spinosad 0.9% topical suspension, which kills live lice and eggs

A healthcare professional can identify the most appropriate treatment for each individual.

Some people may also use a lice comb alongside these treatments to help remove eggs and lice from the hair.

Lice live on a person’s head, laying eggs at the roots of hairs. They are common in children and can easily transmit with close physical contact. They are not a sign of poor hygiene or related to pets.

Treatments for lice typically involve OTC or prescription medications. These treatments typically kill live lice but do not affect the eggs. This means it may take several treatments over 2–3 weeks to eradicate head lice.

People can speak with a healthcare professional for further information about treating lice.