It's Louse-y! How Long Do Lice Live?

how long do lice live

how long do lice live

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It's Louse-y! How Long Do Lice Live?

There are 3 types of lice: head lice, body lice, pubic crab lice. Head lice, with a lifespan of 40 days, live the longest among the 3, followed by body and pubic lice which live up to a month. Both head and pubic lice need a regular supply of human blood to survive (unlike body lice!) and can perish within 24 hours without a human host to "feed" from.

Dealing with head lice is a part of school life. Believe it or not, there are 6–12 million cases of head lice in the United States each year. It’s a great leveler, though, with children of all socioeconomic class suffering from it equally.1

But where do these lice come from? Not from thin air, of course. It’s believed that they existed from the beginning of the time. Dried up head lice and their eggs called nits have been found on the hair and scalps of Egyptian mummies.2

The cases of head lice are on the rise of late and if the latest headlines are anything to go by, there’s something called “super lice” that’s making it appearance on the Americans’ heads. Super lice are actually lice that have developed resistance to over-the-counter lice killer shampoos and potions like Pyrethroid products used for many decades to effectively treat lice.3 This has only added to the distress of the kids and their parents.

The interesting thing about these parasites is that they have their preferences for certain heads, too. Head lice found in the US have an affinity for hair that is round in cross-section and do not thrive on hair that is ovoid in cross section like that of African Americans’ with extremely curly hair. If you’re thinking Africans are really lucky to not have to deal with head lice at all, you’re wrong because Africans have their own brand of head lice with claws adapted for grasping oval hair shafts.4

So What Are Lice?

Lice are wingless insects that are parasites and survive on the host’s blood. They are specific to certain hosts. Interestingly, they are site specific, too, crawling around largely on one particular area.5

There are three kinds of lice found on humans:

Head Lice

Head lice are tiny insects; the size of an adult louse is about 1/8 inch in length. They are parasites and feed on human blood. They come in dirty white to grayish black and spend their entire life cycle in the hair. They are spread through close physical contact with a person who is infested or by using things like comb or clothing that belong to him/her.6

Body Lice

Evolved from head louse, body louse lives between the human skin and clothing. Largely found on parts of the body where the skin folds, the adult lice are 2-4mm in length and gray in color. Body lice are sensitive to body temperature and abandon a dead body instantly and do not stay on bodies with elevated temperature. They are spread through close body contact and also through bedding and furniture.7

Crab Lice

Also called adult pubic lice, crab lice inhabit the pubic hair on the human body. They are very small (about 2mm long) and are yellow-grey or dusky-red color and have six legs. Apart from the pubic hair, the lice are also found in the hair in underarms, legs, chest, abdomen, back and face. Pubic lice are often spread through sexual contact.8

There is a common misconception that lice are a sign of being dirty, which is not true. It has been found that most children in the US infested with head lice bathe regularly and wear clean clothing.9

How Long Do Lice Live?

Head Lice: The egg of a louse, also called nit, hatches in about 10 days from being laid. It takes 10-12 days for a nymph to become an adult louse. This adult louse can live up to 40 days.10

Body Lice: Body louse, too, lives up to a month and can lay about 200-300 eggs (6-9 eggs a day) before it perishes. They lay the egg on the fibers of the clothing or on the body hair close to the clothing. Eggs hatch in 5-10 days.11

Pubic Crab Lice: Pubic lice don’t live as long as other lice do; their lifespan is less than a month. An adult female louse lays around 30 nits in her lifetime. Each egg gets implanted to the shaft of the hair and is often hatched in 6-8 days.12

Can Lice Survive Outside Human Body?

Head lice and pubic crab lice live in close contact with the human body and need a constant source of blood to survive. For this reason, they cannot live beyond 24 hours if they fall off the human host. Nits of these lice may not hatch at all if they are removed from the human body and young ones, straight from the eggs, need to feed on blood immediately to survive.

But body lice is different. Maybe because they are used to staying on clothing and away from the human body, an adult louse can survive for 3-5 days away from the human host and without its blood meal.13 This makes getting rid of body lice far more complicated than the other two types.

How Do We Get Rid Of Lice?

Internet is abuzz with home remedies to get rid of head lice. Methods like applying various natural lice repellents like mayonnaise, olive oil, vinegar, petroleum jelly, etc on the hair are some of them. But studies have shown that head lice can survive all of these even when they are applied and left on the hair overnight. Even shampooing is found to be of very little use. Moreover, lice don’t drown easily. When immersed in water, they can survive for 14 hours at 86–98°F.14

Combing the hair while it is wet (or wet combing) is found to be useful in eliminating head lice en masse. Combs designed specifically for the purpose–with flat-faced teeth and 0.2-0.3mm space between them–are considered best for the purpose.15

If the head lice situation goes out of control, you need to consult a specialist who could suggest medicated shampoos or oil for the purpose and start the treatment soon. Since head lice and nits do not survive away from the scalp, the treatment needn’t be extended to household items or clothing. In a study conducted on head lice infestation, it is found that head lice do not spread through bed linen or pillows. Changing the pillow case after the treatment, however, will minimize the risk of infestation. The study suggests heating the pillowcase by immersing it in hot water or by putting them in a hot clothes dryer for 15 min is found to be effective in minimizing the risk of infestation.16

Pubic crab lice can also be taken care of in a similar way as head lice. If you are going for the treatment advised by a specialist, you should wear clean underwear after it and send all the used ones, including other clothing, bed linen, etc for a thorough wash in the hot water. Those items that cannot be laundered should be dry cleaned or stored in a covered bag for a few days just so the lice on them die. Even after the treatment, the nits might stay on the hair shaft; they need to be handpicked and destroyed.17

In the case of an acute infestation of body lice, treatment with insecticides may be necessary. In normal circumstances, getting rid of them is not that difficult. All you need to do is give your body a good scrub, change your clothing and do not use them for a couple of weeks, so the lice on them die. If the ambient temperature is raised, the lice (except nits) die within four days. The lice that hatch out of the eggs can be brushed away. These lice on the clothing can be eliminated by changing its temperature, either by heating or cooling them. A hot water wash or a few hours in the freezer would eliminate them. Body lice could also remain in bedding, so they need to be cleaned, too.18

Now that you know getting rid of lice is not such a big deal, start working on your strategy right away.

References   [ + ]

1, 14.Managing Head Lice, University of Nebraska-Lincoln.
2.Head Lice FAQs, NAP.
3, 5, 6, 9.Head Lice FAQs, Iowa State University.
4.Head Lice, UCIPM.
7, 11.Body Lice, Department of Medical Entomology.
8.Pubic Lice, NHS.
10.Head Lice, University of Florida.
12.Pubic Crab Lice, Department of Medical Entomology.
13.Human Lice, The University of Tennesse.
15.How To Get Rid Of Head Lice And Nits, NHS.
16.Speare, Rick, Christine Cahill, and Genelle Thomas. “Head lice on pillows, and strategies to make a small risk even less.” International journal of dermatology 42, no. 8 (2003): 626-629.
17.Pubic Crab Lice, CDC.
18.Facts About Lice, Norweigian Institute of Public Health.

Disclaimer: The content is purely informative and educational in nature and should not be construed as medical advice. Please use the content only in consultation with an appropriate certified medical or healthcare professional.

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