The life cycle of lice begins as an egg, or nit. From there, they can live up to 30 days on a human but no longer than 24 hours without a human host. Female lice can lay up to six eggs per day.
Head lice (singular “louse”) are a common health condition, especially in children. These stubborn insects may be difficult to remove from the hair and can be quite contagious.
Symptoms of head lice include visible detection of lice in the hair, and an itching, tingling, or tickling sensation on the scalp.
Lice are parasitic insects. They need a host to provide nourishment so they can live. They form a parasitic relationship with humans as their host, with blood from the scalp as their source of nourishment. Head lice live close to the scalp, and sometimes in the eyelashes and eyebrows.
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Lice have six claws designed to hold onto a single hair shaft. They also use their claws to crawl down toward your scalp when it’s time to feed. Head lice can’t fly, hop, or swim.
However, lice that are in water like in a bathtub or swimming pool are still tightly attached to the hair, and can survive underwater for up to eight hours. If the insects fall off their host into the water, they’ll die because they become separated from their food source.
The life cycle of a louse begins as an egg, also called a nit. The nit is a whitish-yellow speck that is about 1 millimeter in length. It attaches itself firmly to an individual hair strand close to the scalp.
After 7 to 10 days, the nit hatches and becomes what is known as a nymph, or a young louse. Nymphs are usually between 1.1 and 1.3 millimeters, and tan or white in color. Nymphs mature into adult lice within about 9 to 12 days.
Mature adults don’t tend to grow larger than 2 millimeters, and female lice are larger than males. Mature lice live for about three to four weeks.
Immediately after lice eggs hatch, the nymphs need food. Using their claws to crawl from the strands of hair to the scalp, young adult and mature lice feed on the host’s blood multiple times a day.
As long as there’s a food source readily available, an adult louse can live for as long as 30 days on a human. However, lice can continue to multiply. Female lice lay up to six eggs each day.
Although lice can spread on inanimate objects, they won’t spread between you and your pets. Even pets with hair, like dogs and cats, don’t spread lice.
Adult lice can’t live longer than 24 hours or so on nonhuman surfaces like carpets, hardwood floors, clothing, furniture, sports helmets, headphones, or hair accessories. However, if you have identified lice in your home, isolate and wash those items and areas within at least 72 hours.
Nits can’t live without a human host. They need the warmth of the scalp for incubation before they hatch. They need the nourishment they get from human blood as soon as they’ve hatched. Nits that are dislodged from a hair shaft will most likely die before they hatch.
Head lice don’t live very long without a human host, but can transfer from one person to another easily through close personal contact. It’s important to treat lice immediately and thoroughly to avoid an infestation.
Medicated shampoos are designed to kill adult lice and nits. Examples include NIX and RID. These and other brands may contain ingredients such as pyrethrins and pyrethroids. Unfortunately, shampoos that contain pyrethroid may no longer be effective in treating lice.
A doctor can also prescribe medicated shampoos, including malathion (Ovide), benzyl alcohol (Ulesfia), spinosad (Natroba), and ivermectin (Sklice).
You shouldn’t use medicated lice treatments on children younger than 2 months old. Talk to your doctor about alternative treatment methods.
Vacuuming carpets and upholstered furniture prevents lice from crawling onto a new host before they die. Wash bedding, clothing, and washable toys like stuffed animals in hot water. Tumble dry on high heat for at least 20 minutes to kill lice.
At home remedies for lice removal
Treating lice at home without medicated shampoos hasn’t been as widely studied. However, there are some methods that could be effective in treating lice at home. Some options include:
Essential oils haven’t been proven to always kill lice. However, some people have tried applying plant oils like tea tree, anise, or ylang ylang to the hair.
Applying compounds to the hair to smother lice is another natural approach. Examples of products that may be used to smother lice include:
- petroleum jelly
- olive oil
Wet combing involves applying conditioner to wet hair and using a very fine-tooth comb known as a nit comb to remove lice and nits from the hair. This should be repeated every three to four days until it’s been two weeks since you’ve seen any lice or nits.
How do I know if lice are gone?
Treating lice can be stressful. Ideally, your child should be lice- and nit-free about two weeks after initial treatments. Continue to check your child’s hair frequently for lice and nits.
If after two weeks your child still has lice present or their scalp appears inflamed or infected, call their pediatrician. Your child may need a prescription treatment.
If you aren’t sure if your child’s lice are gone, you can purchase a black light and shine it on your child’s hair and scalp. Live nits will glow when they’re exposed to black light.
Because young children often transmit lice, it can be difficult to take preventive measures. They may not understand the importance of preventing head-to-head contact. However, there are some steps you can take:
- Teach your child to avoid head-to-head contact with others, and refrain from playing with, or fixing other children’s hair.
- Teach your child to avoid sharing personal care items like brushes, combs, hats, scarves, and jackets.
- Examine your child’s hair every three to four days if lice have been reported at their day care or school.
To keep lice from coming back, take the following steps:
- Wash all bed linens, towels, and clothing in very hot water that is at least 130°F (54°C), followed by the hot cycle of your dryer for 20 minutes.
- Dry-clean any items you can’t wash. If this isn’t possible, you can place them in large, sealable bags for at least 72 hours so the lice can die.
- Thoroughly vacuum carpets and upholstered furniture. Carefully dispose of the vacuum cleaner bag afterward.
- Separate haircare products and items like ponytail holders, combs, hairbrushes, headbands, and barrettes, and soak them in rubbing alcohol or a medicated shampoo. You can also wash them in very hot water, such as in the dishwasher.
Getting rid of head lice can be time-consuming, but a case of head lice is not a health hazard. Lice don’t carry disease and don’t harm the head or scalp.
But you can prevent head lice by not sharing combs, hairbrushes, hair accessories, towels, bedding, hats, or scarves with a person who has head lice.