Facts of Lice

What are lice?

Lice are wingless parasites that live off human blood. They do not jump or fly! They are usually 1-3 mm in size and are sesame shaped. They are gray in color but after feeding they look reddish brown. It has one pair of antennae on the head and three pairs of legs on the thorax near the head.  Each leg ends with a single claw that helps the louse cling to hair. Lice inject saliva into the scalp after biting, which can cause a mild local allergic reaction. Lice cannot survive without human blood for more than 72 hours.
A louse can lay 3 to 6 eggs daily and between 50 to 150 eggs during its lifespan, which is usually around a month. The term nits refers to a louse egg regardless of whether it contains a viable embryo or not.  A nit can also refer to a leftover shell.
Louse eggs are generally laid within 1 cm of the scalp as they need warmth to develop and hatch. Nits are beige to brown in color and are oval shaped (about 0.8mm). The louse will glue each egg to the hair shaft at an angle, thus when detached nits appear to be tear drop shaped. The glue serves as a protective shell for the developing embryo. Nits will appear darker as long as it contains the embryo, afterward they will appear clear to white.  Eggs take around 7 to 10 days to develop into a nymph, which will then emerge from the protective shell. It will then start feeding on its human host in order to survive and develop. The nymph goes through three stages before it reaches adulthood. It takes about ten days for a nymph to reach adulthood. Once it reaches adulthood it will mate and begin to lay eggs which begin the cycle all over again.  Imagine what happens when lice are left untreated!!


How are lice spread?

Lice are normally spread through close head-to-head contact because they cannot jump or fly. However, sharing items of an infested individual such as brushes, hats, beds and clothing which may contain lice on them can also be a mode of transmission. Reports estimate that 6-12 million people are treated annually for head lice. Head lice are most common among school aged children. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.


Can you catch head lice when swimming in a pool or lake?

Lice grasp the hair very firmly while in water and sort of hold their breath in order to survive. This is why when a person showers the lice do not just fall off and go down the drain. Therefore, swimming with someone who has lice does not put you at a greater risk of catching head lice when compared to other activities.


What are the signs and symptoms of head lice?

The most common symptom is itching which is caused by the local allergic reaction from the bites. Many times the bites will get infected from children scratching their heads with dirty fingernails. Head lice are most active during the night so many people will have a hard time sleeping. Occasionally people will see a bug crawl across their forehead or notice one on their brush.

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How can I tell the difference between nits and dandruff?

Nits are firmly attached to the hair shaft and will not move when rubbing your finger over it. Nits are more beige to brown in color and have a glossy appearance, whereas dandruff is more white and opaque. Nits are always the same oval shape and attached to the hair at an angle. Dandruff will vary in shape and size. Protein is commonly mistaken for nits because it will not move when you blow at it. However, it is usually more white, linear and wrapped around the hair shaft.

Can my pets get head lice?

NO! Lice are human parasites and are not spread through pets.

Do lice carry any diseases?

No! Lice are parasites that do not carry diseases. However, infection can occur if a child is scratching the bites with dirty fingernails.

Can a nit hatch off your head?

A nit really needs human warmth in order to incubate and hatch (takes around 7-10 days). If the environment is the right temperature, it can hatch and become a tiny nymph, but most likely would not survive because it needs human blood immediately. Someone would have to be real close by for it to find a human host and continue living.

How long can a louse survive without human blood?

Usually not more than 48 hours but some studies have shown up to 72 hours.

Who should be checked if a case of head lice is discovered?

All close contacts should be checked so that re-infestation does not occur. This includes parents, siblings, babysitters, classmates and neighbors. Close contacts are very likely to have head lice especially if it is a severe infestation. I recommend that if a case of lice is discovered in the family all family members should be thoroughly combed. Very often another family member can have just a few nits or one louse which can easily be missed when checking without a comb. Although at the time it is mild, within a few weeks it can become a full blown infestation.

What needs to be done in the house in order to prevent re-infestation?

Items in the house that come in close contact with your hair should be put away for two weeks or washed on a normal temperature setting. This includes linen, towels, hats, hair accessories, brushes, and clothing that were recently worn.  Couches or other fabric covered furniture should be vacuumed. Lice are really human parasites and need human blood in order to survive; however, if an individual was sitting on the couch and a louse came off their head, the next person to sit down may be the new host! Spraying furniture with pesticides is a health hazard that is costly and unnecessary; vacuuming does the trick.

What steps should be taken in a classroom when a case of head lice is discovered?

The entire class should be checked by a professional to see if anyone else has lice to prevent further infestations. Many times children get head lice from school and if the class is not checked your child may come home with it again. Items in the classroom that are fabric and come in close contact with hair should be vacuumed or put away for two weeks. Coats should not hang close to each other when on hooks, it is best to put coats in separate shopping bags and then onto the hooks.

What lice treatment options are available and which ones are successful?

Manual removal with a very fine tooth comb is the most effective way of eradicating head lice. As of now there is no lice shampoo that in 100% ovicidal (able to kill nits). Some shampoos may kill the lice but from overuse/misuse there is major resistance to them and very often live lice are seen even after treatments.  Additionally, since shampoos do not kill nits, the nits hatch 7 – 10 days later and the cycle starts again. Not every nit hatches the same day so even with retreatment a week later, chances are you will see live lice again over the next week or two. The shampoos also recommend combing to remove the nits, so if you will have to comb anyways then why put toxic shampoos on your child’s head? (Lice are easier to remove than nits since they are larger, and they will come out when you comb.) There are a number of home remedies that people have tried such as sleeping in olive oil for two weeks or putting margarine in the hair. These methods are not only uncomfortable, but there isn’t a high success rate and there are no studies to prove that these methods work. The worst thing you can do is put your child to bed with plastic wrapped around their head.  Many shampoos have side effects and are contraindicated for certain people so one must read the instructions and warnings carefully if they choose to use a shampoo before combing.

Do you recommend using a lice shampoo?

I DO NOT recommend the use of any shampoo prior to coming to us since our combing technique is 100% successful without it and much safer.

What are the different types of lice shampoos and their side effects?

Over the counter shampoos:
Pyrethrins: (RID, A-200, Pronto, R & C, and Triple X)
Since Pyrethrins are a naturally occurring pyrethroid extract derived from chrysanthemum flower, if one is allergic to chrysanthemum or ragweed they should not use it. It can only kill live lice and retreatment is recommended in 9 -10 days to kill new hatched lice before they lay new eggs. According to the Center for Disease Control and American Academy of Pediatrics treatment failures can be common depending on the lice resistance in the patient’s geographic location.
Permethrin lotion 1%: (Nix)
Permethrin is a synthetic pyrethroid and should not be used in children under two. It can only kill live lice and retreatment is recommended in 9 -10 days to kill new hatched lice before they lay new eggs. It may continue to work for several days after treatment but a second treatment is often necessary.  According to the Center for Disease Control and American Academy of Pediatrics treatment failures can be common depending on the lice resistance in the patient’s geographic location.
Prescriptions shampoos:
Malathion lotion 0.5%: (Ovide)
Malathion is an organophosphate. It is pediculicidal (kills live lice) and is partially ovicidal (kills nits). A second treatment is recommended if live lice are seen after 7 -9 days. Malathion should only be used for people over 6 years of age. It is flammable (high alcohol content) and should not be used near hair dryers, electrical heat sources and one should not smoke while it is in their hair.  A major risk of accidental indigestion is respiratory depression.
Lindane 1%: (Kwell)
Lindane is an organochlorid. Lindane is FDA approved but should not be used as a first line of treatment because of its side effects. It can be toxic to the brain and nervous system and cases of seizures in children have been reported.  It should not be used in infants, people with a seizure disorder, pregnant or breastfeeding women or in people who have irritated skin or sores. Resistance has been reported worldwide for many years.
Permethrin 5%: (Elimite)
It is usually used to treat scabies and no case-control studies have reported efficacy to date. However, one study did suggest that lice resistant to permethrin 1 % will not die from higher concentrations such as permethrin 5%.
Benzyl Alcohol: (Ulesfia)
It kills live lice by closing their respiratory spiracles but it does not have ovicidal activity (does not affect nits). It may cause skin and eye irritation. It should not be used in premature infants because intravenous use of benzyl alcohol has been associated with neonatal gasping syndrome. It is approved for infants 6 months and up.
Ivermectin lotion: (Sklice)
This shampoo affects the ability of the lice to feed so they end up dying from starvation. It does not directly kill the nits however; once a nit hatches the nymph may have a hard time feeding if exposed to ivermectin.  This product is new to the market so there is not much data available yet and most insurance companies will not cover it.
Prescription oral agents:
Sulfamethoxazole/Trimethoprin: (Bactrim, Septra)
One study showed that using this antibiotic along with permethrin 1% may have had increased effectiveness but is not currently approved by the FDA for head lice treatment.

How can I prevent re-infestation?

Make sure all close contacts are checked carefully. It is best for all family members to be combed. Make sure to clean the house properly. You can check out our tips on cleaning the house (add link) for a full list of items to clean. The most important thing in preventing re-infestation is to comb every few days for the next two weeks and to have a recheck one week after initial treatment. We give our patients a complimentary recheck a week later to ensure that treatment was successful.

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