This is the most common way to get head lice - Nazzy Pakpour

56,557 views ・ 2025-03-13

TED-Ed


Please double-click on the English subtitles below to play the video.

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The six-legged creature creeps down the canopy,
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extends its slender trunk, and pierces the ground.
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Up comes blood.
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This is no regular forest.
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Living where the scalp meets the hair,
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these nightmarish figures are, in fact, sesame seed-sized insects,
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otherwise known as head lice.
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The earliest archaeological evidence of humans’ close-knit relationship with lice
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is a fully preserved egg,
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discovered in the hair of a 10,000-year-old Brazilian mummy.
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And it seems that for as long as we’ve had lice,
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we’ve fought hard to get rid of them.
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Nit combs, the fine-tooth brushes used to remove lice
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and their sticky eggs
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have been found among the ancient remains of cultures across the globe.
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This battle continues today,
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as it's estimated we spend billions of dollars each year treating infestations.
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01:04
So, why are lice so difficult to get rid of?
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There are at are at least several thousand louse species,
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as nearly all mammals deal with these parasites.
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Humans are pestered by three different types,
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each specialized to roam its own unique bodily terrain.
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Pediculus humanus capitis live exclusively on heads
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and are equipped with hook-like claws that are perfectly fitted to human scalp hair.
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Pediculus humanus humanus, or body lice,
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spend most of their lives embedded in clothing and bedding,
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and crawling onto any nearby body part for their feedings.
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In order to thrive in these changing environments,
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body lice are more resilient to fluctuations in temperatures and humidity.
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Meanwhile, pubic lice, also known as crab lice,
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are an entirely different species.
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While they also live on hair,
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their claws are larger than head lice,
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as they’re fitted to grasp onto the thicker cuticles found in pubic areas.
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Among these three varieties, head lice are the most common.
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In the US alone, it’s estimated 6 to 12 million children
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deal with infestation each year.
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Contrary to popular fears about catching lice from hats or hairbrushes,
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most cases spread through direct head-to-head contact.
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You see, head lice can only survive about 24 hours without a host to feed on.
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They’re wingless and they can’t jump,
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so the only way they can infest a new head is to crawl.
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They can detect a new host by using their antenna to home in on body heat
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and other chemical compounds that naturally emanate from the scalp.
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Once they arrive on a new head, they're ready to eat.
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A louse pierces the scalp with a retractable tube-like mouth
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and releases a special saliva
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that contains factors that open up blood vessels and help prevent clotting.
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This chemical cocktail is also what makes the scalp feel itchy.
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Symbiotic bacteria living in louse’s gut complement this blood meal,
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by providing the additional vitamins and minerals that the louse needs to survive.
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The scalp is also where lice mate.
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Once mated, female lice can lay up to 8 eggs, called nits, per day.
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She deposits each egg on the hair,
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just a few millimeters above the scalp, and coats it with a sticky nit sheath,
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which provides hydration and other factors the egg needs to survive.
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This sheath hardens,
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tightly cementing the nit to the hair until it hatches 8 to 9 days later.
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You can’t get rid of a lice infestation
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without taking care of this sticky egg problem.
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While insecticide shampoos kill hatched lice,
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they’re ineffective against eggs.
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And nit sheaths are strong, waterproof, and resistant to chemical breakdown.
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Scientists hope to bring some new tools to this old battle
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by identifying treatments that can dismantle individual components
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in the nit sheath,
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like those that hydrate the egg and keep it alive.
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But until then, there’s only one tool that’s been shown
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to effectively remove eggs,
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and it’s the same one that was used by ancient cultures:
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a fine-toothed nit comb.
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Lice are certainly stubborn survivors,
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but perhaps one day, with the help of science,
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these ancient parasites will haunt our nightmares— and scalps— no more.
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