No. Blood type plays no part in how the CDC, the AAP or the NIH’s MedlinePlus explain head lice. All three explain head lice the same way: they are insects that feed on human blood, and the main way a person gets them is head-to-head contact with someone who already has them. Anyone can get head lice. So when one person in a house keeps getting them, the thing to examine is how heads come together, not what is in anyone’s blood.
Head Lice Feed on Blood, But Feeding Is Not How They Find a Head
Head lice do feed on human blood, but feeding happens after a louse arrives, not before. The CDC’s overview of head lice describes them, or Pediculus humanus capitis, as parasitic insects that feed on human blood and usually live on your scalp, roughly 2 to 3 mm long, about the size of a sesame seed. The AAP’s guidance for parents says the same thing in plainer terms: head lice feed on small amounts of blood from the scalp. The CDC and the AAP both state that head lice move by crawling and cannot hop or fly, and the AAP notes that live lice are hard to find because they avoid light and move quickly. A louse lands when hair touches hair and stays because it can feed where it landed. The CDC says adult lice can live on a person’s head for about 30 days, and that they will die within two days if they fall off a person and cannot feed. Contact, then a meal: blood group has no place in that sequence.
What Does Change the Odds of Getting Head Lice
Age and contact are what change the odds, plus one note about hair. MedlinePlus says children ages 3 to 11 and their families get head lice most often, and gives the reason in the next line: young children often have head-to-head contact while playing together. The CDC attaches a number to the same age band, estimating 6 to 12 million infestations each year in the United States among children 3 to 11 years of age. It also reports that some studies suggest girls get head lice more often than boys, probably due to more frequent head-to-head contact. Behavior again, not biology.
Hair is the one physical feature the CDC raises. It reports that in the United States, infestation with head lice is much less common among African American persons than among persons of other races, and that lice may have claws that are better adapted for grasping the shape and width of some types of hair, but not others. That is hair shape, not blood, and it is not armor: the AAP says lice can attach to the hair of anyone’s head, and that anyone can get head lice. We take that question further in our look at whether lice are more common in certain hair types.
Cleanliness is not on the list at all. The CDC says getting head lice is not related to cleanliness of you or your environment, MedlinePlus says personal hygiene and cleanliness have nothing to do with it, and the AAP says it does not matter if the hair is clean or dirty. Families who arrive at our clinic braced for a lecture about housekeeping can let that go.
How Head Lice Get From One Head to Another
Hair touching hair is the route, and the rest are ranked below it. The CDC says head lice mainly spread by direct contact with the hair of a person infested with lice, and calls head-to-head contact the most common way to get head lice. The AAP describes the main way head lice spread as close, prolonged head-to-head contact. The other possibilities are worth knowing, if only to stop worrying about the ones that barely matter.
| Route | What the CDC, the AAP and MedlinePlus say |
|---|---|
| Head-to-head (hair-to-hair) contact | The most common way to get head lice (CDC); the main way they spread (AAP) |
| Hats, scarves, coats, sports uniforms, hair ribbons, barrettes | Possible, although not as common (CDC); a very small chance, and only if used within 2 days before head lice were found and treated (AAP) |
| Combs, brushes, towels | Possible (CDC); rarely (MedlinePlus) |
| Beds, couches, pillows, carpets or stuffed animals recently in contact with an infested person | Possible, although not as common (CDC); the risk from a louse that has fallen onto a rug, carpet or furniture is very small (CDC) |
| Swimming pool water | Lice can survive under water for several hours but are unlikely to spread in a pool, and chlorine levels in pool water do not kill them (CDC) |
| Wigs and hairpieces | Extremely unlikely, especially if not worn in the past 48 hours by a person with head lice (CDC) |
| Pets and other animals | Animals do not get or spread head lice (CDC) |
The prevention advice that follows is short. The CDC’s list: avoid hair-to-hair contact during play, do not share clothing such as hats, scarves, coats, sports uniforms, hair ribbons or barrettes, and do not share combs, brushes or towels. MedlinePlus adds the things children put on their heads, such as headphones, hair ties and helmets. The AAP’s contribution is a habit rather than a rule, saying regular checks are a good way to spot head lice before they have time to multiply.
Check the Scalp Instead of Guessing
The question gets settled on the scalp. The CDC says finding a live nymph, a baby louse, or an adult louse on the scalp or hair is the best way to diagnose a head lice infestation, and MedlinePlus says a diagnosis usually comes from seeing a louse or nit. That is harder than it sounds: the CDC says adult and nymph lice are very small, move quickly and avoid light, so a magnifying lens may help.
The AAP sets the check out as a comb-out:
- Seat your child in a brightly lit room and part their hair.
- Wet the hair.
- Comb through small sections with a fine-tooth louse or nit comb.
- After each pass, wipe the comb on a wet paper towel, then examine the scalp, the comb and the towel.
- Repeat until you have combed through all of the hair.
Where you look matters. The AAP says the easiest place to find them is at the hairline at the back of the neck or behind the ears, and the CDC says you will often see nits on hair behind the ears and near the back of the neck. Nits look like small white or yellow-brown specks attached firmly to the hair near the scalp, and the AAP’s test is simple: nits stay stuck, while dandruff, dirt and hair spray droplets do not. The CDC says misdiagnosis of head lice infestation is common, and adds a distance rule, that nits attached more than 1/4 inch from the base of the hair shaft are almost always hatched or dead.
Do not judge by itching alone. The CDC says it may take four to six weeks for itching to appear the first time a person has head lice, and that people may have no symptoms, particularly with a first or light infestation. If you are not sure, the CDC’s advice is to see your healthcare provider.
What the Guidance Says About Treating a Whole Household
The AAP’s first instruction is to call the child’s doctor before beginning any head lice treatment. It also says head lice medicine should be used only when it is certain that your child has living head lice, that medicine should be applied by an adult and never by a child, and that package directions should be followed exactly as written. The CDC’s treatment page says to treat an active infestation, to check all household members and other close contacts, and to treat infested household members, close contacts and the people they share a bed with at the same time. Reinfestation after successful treatment sits on the CDC’s own list of reasons treatment fails.
Whether a second round is needed depends on the medicine, which makes it a question for the label and the prescriber. The CDC says some medicines kill lice and eggs, with retreatment usually not required for those, while others kill lice but not eggs, so retreatment is recommended, and it says to talk to your healthcare provider before re-treating. The AAP notes that over-the-counter treatments sometimes are not the most effective, that lice can be resistant to their active ingredients in some communities, and that the likelihood of resistance varies across the country, so its advice is to call the pediatrician first.
Two things to avoid. The AAP says not to use home remedies such as petroleum jelly, mayonnaise, tub margarine, essential oils or olive oil, because no studies prove they work, and the CDC says it has no scientific evidence that suffocating head lice with mayonnaise, olive oil, margarine, butter or similar substances works. The AAP is blunter about the dangerous end of the shelf: never use gasoline or kerosene, or medicines made for use on animals. The CDC says not to use fumigant sprays or fogs, which are not necessary and can be toxic if inhaled or absorbed through the skin.
Frequently Asked Questions
Is there a blood type that head lice avoid?
No, and none attracts them either. The guidance from the CDC, the AAP and MedlinePlus ties head lice risk to contact and age. MedlinePlus describes lice as parasites that need to feed on human blood to survive and says they spread by close person-to-person contact. The blood is food once a louse is already there, not a signal that draws it.
Why does one person with lice itch and another does not?
Itching is an allergic reaction to louse bites, and reactions vary. The CDC calls itching the most common symptom and lists irritability and sleeplessness with it; MedlinePlus explains the sleep trouble by noting that head lice are most active in the dark. The AAP says itching can last for weeks after the lice are gone, so an itchy scalp after treatment is not proof that treatment failed.
Can head lice spread in a swimming pool?
They are unlikely to. Chlorine does not kill head lice, the CDC says, and lice can survive under water for several hours, but a pool is not where they spread. A pool is neither a treatment nor much of an exposure. The shared towel afterward is the part of a pool trip worth watching.
Can our dog or cat give the family head lice?
No. Animals are neither hosts nor carriers, the CDC says. These insects live on human scalps and feed there, so a dog or cat is not a reservoir passing lice between family members and does not need anything done about it when a child has head lice. Treat the people, and leave the pets out of it.
Do head lice carry disease?
No. The CDC says head lice do not transmit any disease and are not considered a health hazard, and the AAP says they do not put your child at risk for any serious health problems. The one complication both name comes from scratching: sores on the head that can sometimes become infected with bacteria normally found on the skin.
How fast does one louse become an infestation?
A new generation reaches adulthood in about 12 to 14 days, by the AAP’s count. The CDC says an adult female can lay about six eggs each day, that nits take about a week, a range of 6 to 9 days, to hatch into nymphs, and that nymphs need about seven days to mature. The AAP adds that the cycle can repeat every 3 weeks if head lice are left untreated.
Do we have to clean the whole house?
Not the whole house. The CDC says spending much time and money on housecleaning is not necessary to avoid reinfestation. It does advise washing and drying the clothing, towels and bed linens used in the two days before treatment, on the hot water cycle at 130 degrees Fahrenheit with high heat drying, sealing what you cannot wash in a plastic bag for two weeks, and vacuuming where the person sat or lay.
How Lice Lifters of Ocean County Can Help
A head check ends the guessing. At Lice Lifters of Ocean County we check the whole family, not only the person who started scratching, because one missed head can bring a case back. When we find live lice, our professional lice treatment is non-toxic and finished in one visit, so you are not left managing a string of steps at home. Same-day appointments are available, which matters on the day a check turns up something you were not expecting. Our 30 Day Guarantee applies when the whole family is checked. If you would rather have an answer than another evening under a bright lamp with a comb, book a head check and bring everyone who shares a roof.
