My son attends a preschool, and we just found out that head lice are going around. This was a source of some concern for my son, because what he knows about it starts with “bugs in hair, bugs in hair!” and ends with “they make you itch!” So, naturally, he’s had some questions about them. Lots of questions. And, to tell the truth, so do I. Because I remember distinctly that, when I grew up, there was a social stigma associated with having lice. Not just because you had bugs in your hair, but because it meant you were perceived as filthy and dirty.
That’s hardly a fair assumption, of course. My son’s daycare and preschool is a wonderful place and they take hygene seriously. But it’s hard to shake beliefs that get ingrained during childhood. Also, it turns out that I know next to nothing about head lice. Beyond “bugs in hair, bugs in hair!”
What are head lice?
That picture up there? That’s a head louse – Pediculus humanus capitis – an obligate ectoparasite of humans, which is a fancy way of saying it’s a parasite that lives on human skin and needs to exploit a host as part of its life cycle. Pediculus humanus capitis feeds by biting the skin and injecting an anti-coagulant in order to suck blood (producing a dark red poop when digested), and generally colonizes the scalp (particularly the nape of the neck and the back of the ears).
According to the CDC,
The life cycle of the head louse has three stages: egg, nymph, and adult.
Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the scalp. They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.
Nymphs: The egg hatches to release a nymph. The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts and become adults about 7 days after hatching.
Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white The number 5. In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.[/quote]
Wikipedia expands on the definition of “nit” a little, stating that “the term nit refers to an egg without embryo or a dead egg”.
Pediculus humanus capitis requires anywhere from 8 to 24 days to mature from a newly-hatched nymph to a sexually mature adult, depending on temperature and access to blood. Once mature, a female can lay 3-4 eggs per day for pretty much rest of her life (which can be up to 30 days from hatching). This is under optimal conditions of course.
Ick. So, how does it spread?
Turning to the Centers for Disease Control once more,
Head lice are mainly spread by direct contact with the hair of an infested person. The most common way to get head lice is by head-to-head contact with a person who already has head lice. Such contact can be common among children during play at:
- home, and
- elsewhere (e.g., sports activities, playgrounds, camp, and slumber parties).
Uncommonly, transmission may occur by:
- wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person;
- using infested combs, brushes or towels; or
- lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person.
Reliable data on how many people get head lice each year in the United States are not available; however, an estimated 6 million to 12 million infestations occur each year in the United States among children 3 to 11 years of age. Some studies suggest that girls get head lice more often than boys, probably due to more frequent head-to-head contact.
Interestingly, they note that (in the United States, at least) African-Americans are less likely to have an infestation than other races. They don’t quite know why, but speculate that the most common head louse in the United States is not well adapted to grasping the shape and width of some types of hair. Sadly, if you’re African-American and reading this, you can’t simply assume that you’re immune to head lice infestations. After all, “less likely” is not the same thing as “can’t get it”.
The CDC also states the following: “Head lice move by crawling; they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. Spread by contact with clothing (such as hats, scarves, coats) or other personal items (such as combs, brushes, or towels) used by an infested person is uncommon. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.” To be safe, you probably still don’t want to share hats or combs or the like. But you should really avoid headbutting.
How do I know if I (or someone else) has lice?
Unsurprisingly, the CDC has a lot to say about this. Symptoms include:
- Tickling feeling of something moving in the hair.
- Itching, caused by an allergic reaction to the bites of the head louse.
- Irritability and difficulty sleeping; head lice are most active in the dark.
- Sores on the head caused by scratching. These sores can sometimes become infected with bacteria found on the person’s skin.
However, they also note that “Misdiagnosis of head lice infestation is common. The diagnosis of head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person…. If crawling lice are not seen, finding nits attached firmly within ¼ inch of the base of hair shafts suggests, but does not confirm, the person is infested. Nits frequently are seen on hair behind the ears and near the back of the neck. Nits that are attached more than ¼ inch from the base of the hair shaft are almost always non-viable (hatched or dead). Head lice and nits can be visible with the naked eye, although use of a magnifying lens may be necessary to find crawling lice or to identify a developing nymph inside a viable nit. Nits are often confused with other particles found in hair such as dandruff, hair spray droplets, and dirt particles.”
Yeah, that’s distinctly a bug. Now what?
Are you shocked to learn that the CDC has information on this as well? No? Me neither. The first thing that they recommend is, after confirming that someone in the household has an active infestation, you should check everyone else in the same household. It’s most likely to spread within a family, after all, as family members have the greatest odds of coming into head-to-head contact.
Pharmacologically speaking, you can use an over-the-counter or prescription medicine to kill the lice and nits. Be sure to follow the directions and, if the infested individual has long hair, consider more than one treatment. The CDC also recommends not re-washing hair for one to two days after treatment, to allow the residue of the medicine to continue to work. After treatment, comb the infested individual’s hair thoroughly to remove lice and nits and then check them around 8-12 hours after treatment. A few live but sluggish lice found during that time generally doesn’t mean that the treatment failed (some are more resistant than others), and you probably won’t need to retreat. If the lice are still active,, however, you may wish to use a different medicine and/or consult with a health care professional. Also, even after the lice appear gone, you should comb the hair with a nit comb every two to three days for the next two to three weeks to ensure the infestation is gone. Also, if the specific medicine you are using has different instructions, follow them.
Any clothing, bed linens, plush animals, etc that the infested individual came into contact with should be washed on hot (130 degrees F or higher) and then dried on the high heat cycle. Items that are not machine washable can be dry-cleaned instead, or sealed in plastic bags for two weeks. Vacuuming furniture and carpets can remove any lice that have fallen from the infested person, but they generally do not survive long off a human (since they are human-exclusive parasites that need human blood to live) so you don’t have to go to extreme measures to sterilize your home.
Kill it. Kill it with fire!
Generally speaking, you don’t actually kill head lice with fire. Not that it wouldn’t work, mind. But they’re living on your skin, so you don’t really want to apply fire. Instead, you apply neurotoxins.
The most common over-the-counter medicines for head lice are pyrethrins, which kill by “targeting the nervous systems of insects”. Specifically, “pyrethrins delay the closure of voltage-gated sodium ion channels in the nerve cells of insects, resulting in repeated and extended nerve firings. This hyperexcitation causes the death of the insect due to loss of motor coordination and paralysis.” So, yes. You’re consigning the little bugs to a slow and agonizing death. But it also functions as an insect repellent, driving survivors from the treated area – sort of the over-the-counter version of displaying your enemies’ heads on pike, I guess.
Note that pyrethrins can affect humans, in sufficient doses. The EPA recommends different daily oral exposure limits for pyrethroids of anywhere from 0.005 to 0.05 mg per kg per day (depending on the specific pyrethroid), and OSHA has set an occupational exposure limit for a standard work day of 5 mg per cubic meter. Note, however, that most lice treatment shampoos run around 0.33% pyrethrins by weight. What does that mean?
well, I weigh 133.35 kg, meaning that my safe limit for daily oral exposure to pyrethroids ranges from 0.66675 mg to 6.6675 mg per day, depending on the specific pyrethroid. Assuming the specific pyrethroid in the medicine is the one in the 0.005 mg per kg limit, I could drink 202 mg of the medicine and generally be all right. (Note: do not do this!) That’s not a whole lot, though, which is why these medications fall under the category of “safe when used as directed“.
Head lice medication cocktails are not a use as directed.