Lice are insects that feed on human blood. They live on the human head, body and pubic area. You get lice by coming into contact either with lice or their eggs.

For head lice, female lice make a sticky substance that holds each egg to the base of a hair shaft. Eggs hatch in 6 to 9 days. Body lice most often lay eggs in clothing seams.

The most common way to get pubic lice is through having sex. Pubic lice on children may be a sign of sexual abuse.

Transmission

Lice crawl, but they can't jump or fly. They can live 1 to 2 days off the body. Head and body lice spread through:

• Head-to-head or body-to-body contact. This often happens within families or among children who have close contact with each other at school or play.
• Clothes stored together. Storing clothes that have lice on them close together with other clothes in closets, lockers or on side-by-side hooks can spread lice. Lice also can spread from stored items such as pillows, blankets, combs and stuffed toys.
• Shared items. These may include clothing, headphones, brushes, combs, towels, blankets, pillows and stuffed toys.
• Contact with furniture that has lice on it. Lying on a bed or sitting on cloth-covered furniture that someone with lice recently sat on can spread them.

Head lice

Head lice spread mainly by direct head-to-head contact. So the risk of spreading head lice is greatest among children who play or go to school together.

Body lice

People who are at higher risk of body lice tend to live in crowded, unclean conditions. These include refugee camps, shelters and homeless camps.

Pubic lice

Having sex with a person who has lice raises the risk of pubic lice.

It's hard to keep head lice from spreading among children in schools or places that provide child care. Policies that prevent hair and head contact between people can help. The chance of spreading head lice from items that come in contact with the hair or head is small. But you can lower your risk of getting head lice by not sharing hair items, such as brushes or things that touch the head, such as hats or scarves.

To prevent body lice, don't have close physical contact or share bedding or clothing with anyone who has lice. Regular bathing and changing into clean clothing at least once a week also may help prevent body lice.

To prevent pubic lice, don't have sex or share bedding or clothing with anyone who has these lice. If you are being treated for pubic lice, your sexual partners also must be treated.

During an exam, you or a healthcare professional may use a magnifying lens and a fine-toothed comb to look for lice.

Head lice

You or a healthcare professional may diagnose head lice after finding live lice in the person's hair or on the scalp. The healthcare professional also looks for lice eggs, called nits, by combing the hair with a special comb called a nit comb. But finding nits does not confirm the diagnosis of live lice.

Body lice

A healthcare professional may diagnose body lice after seeing eggs or crawling lice on clothing seams. You might see eggs or crawling lice on clothing or bedding. You can see body lice on skin when they crawl there to feed.

Pubic lice

A healthcare professional may diagnose pubic lice after seeing moving lice or nits on hair in the pubic area or on other areas of coarse hair, such as chest hair, eyebrows or eyelashes.

To kill head lice and lice eggs, you can use a few methods. Wet combing, smothering or dehydrating are ways to kill head lice. Or you can use medicine available with or without a prescription.

Treatment for any type of lice may involve permethrin or products that have pyrethrin that you put on the affected areas. Both are available without a prescription.

Permethrin is for people 2 months and older. Pyrethrin is for people 2 years and older. For head and pubic lice, use one of these treatments by following package directions. Then remove nits with the comb that's in the package. For the next 2 to 3 weeks, comb out the nits every 2 to 3 days. Repeat the treatment on day nine or 10.

If you have body lice, first bathe with soap and water. That and washing clothes and bedding in hot water may be all the treatment needed.

If you need to treat body lice with medicine, put it on the affected areas at bedtime. Don't put medicine on the face. Rinse it off in the morning. Repeat the treatment on day nine.

What to do when treatments don't work

In some parts of the world, medicines available without a prescription no longer kill lice. Also, these medicines can fail if you don't use them correctly or repeat them as instructed. If these treatments don't work for head lice, your healthcare professional might suggest other medicines.

• Spinosad. Spinosad is a prescription medicine for adults and children age 6 months and older. Apply to dry hair. Leave on for 10 minutes. Rinse with warm water over a sink to keep the lotion from getting on the skin. Don't shampoo hair for 24 to 48 hours. Repeat in seven days if you see lice.
• Malathion. Malathion is a prescription medicine for adults and children age 6 years and older. Put the lotion on dry hair and leave it on for 8 to 12 hours. Then rinse it out using warm water over a sink to keep it from getting on the skin. Don't shampoo hair for 24 to 48 hours. Repeat in seven days if you see lice. This medicine is flammable, which means it catches fire easily. Don't use it with a hair dryer or curling iron or near an open flame.
• Ivermectin. This is a prescription medicine that you take by mouth for head or body lice if other treatments don't get rid of the lice. You can give it to children who weigh more than 33 pounds (15 kilograms). You can repeat it in 7 to 10 days if needed. Don't take this medicine if you are pregnant or breastfeeding. There's also an ivermectin lotion (Sklice) you can get without a prescription. If you use this treatment, don't repeat it without talking to a healthcare professional.

These steps may help you get rid of lice:

• Check other people who live with you for lice and nits. Treat anyone who has signs of lice.
• Comb wet hair. For hair lice, use a fine-toothed comb to remove the lice from wet hair. Repeat every 3 to 4 days for at least two weeks. You can use this method with other treatments. It's often the first treatment for infants younger than 2 months.
• Wash items. Wash bedding, stuffed animals, clothing and hats with hot, soapy water that's at least 130 degrees Fahrenheit (54 degrees Celsius). Dry them at high heat for at least 20 minutes.
• Seal items in plastic bags if you can't wash them. Put items in an airtight bag and seal it for two weeks.
• Vacuum. Vacuum floors and furniture well.
• Wash combs and brushes. Use hot, soapy water of at least 130 degrees Fahrenheit (54 degrees Celsius). Or soak combs and brushes in rubbing alcohol for an hour.

Household pets, such as dogs and cats, don't spread head lice. So you don't need to treat them.

Many people use home products like olive oil to treat head lice. But there's little to no proof that they work.

Most people who have lice don't need to see a healthcare professional. If you're not sure that what you see are lice, call your healthcare professional. For pubic lice, make an appointment with your healthcare professional to check for other sexually transmitted infections.

Here's some information to help you get ready for your appointment.

What you can do

Before your appointment, make a list of:

• The symptoms and when they began.
• All medicines, vitamins and other supplements you or your child takes, including the dosages.
• Questions to ask your healthcare professional.

Basic questions to ask about lice include:

• What's causing the symptoms?
• What else might cause the symptoms?
• How can you tell if there are lice?
• What's the best treatment?
• What happens if the treatment doesn't work?

Be sure to ask all the questions you have.

What to expect from your doctor

Your healthcare professional is likely to ask you questions such as:

• When did your symptoms begin?
• How bad are your symptoms?
• What, if anything, have you tried to ease the symptoms?

What you can do in the meantime

The person with lice should not have close contact with anyone.