The Most Common Allergy In The World

The urushiol molecules in poison ivy have the ability to trigger a harmful immune response in most people because the immune system mistakenly labels them as a threat.

LEARN MORE
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To learn more about this topic, start your googling with these keywords:
- Allergy: A damaging immune response by the body to a substance.
- Allergen: The substance that causes the allergic reaction.
- Urushiol: The allergen in poison ivy and poison oak.
- Allergic Contact Dermatitis: An allergic response caused by contact with a substance that causes rash or lesions at the site of the exposure.
- Langerhans Cell: An immune sentinel that lives in the epidermis of the skin but can travel to nearby lymph nodes.
- Helper T Cell: A type of white blood cell that activates immune responses in the body.
- Thrush: A white skin rash caused by the fungus candida.
- Anaphylaxis: A whole body allergic reaction that can include throat swelling.

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CREDITS
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David Goldenberg | Script Writer, Narrator and Director
Sarah Berman | Illustration, Video Editing and Animation
Aldo de Vos, Know Art | Music

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REFERENCES
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Florian Winau (2021) Personal Communication. Department of Pediatrics, Harvard Medical School.

Tiffany Scharschmidt (2021) Personal Communication. Department of Dermatology, UCSF Medical School.

[Pyronaut_]

I was never told and never even considered that the reaction to Poison Ivy was an allegy, but it makes so much sense that it is.

[SupremeLeaderKimJong-un]

On a whim, I decided to roll around in some poison ivy.
It was a real rash decision.

[AnonymousFreakYT]

My wife has the same reaction to regular English Ivy as to poison ivy. It's super strange - and our kid didn't believe it when he was little. He thought it strange that she couldn't touch the leaf he could. He admitted as an adult that multiple times, he would wipe an English Ivy leaf on something my wife would touch to see if she would immediately break out in a rash.

Of course, her reaction wasn't instant - it took a couple days. So by the time she broke out in a rash, he had forgotten that he had done it. He only made the connection as an adult. And my wife instantly had an "AHA! That explains all the random rashes I had! I always thought it was that the dog had gotten into it without my knowledge!"

[korcommander]

You ever just roll around in poison ivy just to flex your lack of allergy?

[emmettturner]

Just knowing that the reaction was an allergy I had already guessed that Urushiol was the topic here. I did not realize that it was the most common allergy in the world but I did know that most people were allergic, hence one common plant-source being named “Poison Ivy.”

[SgtSupaman]

I always knew poison ivy was safe because I was one of the few not allergic to it. Unfortunately, I seem to have developed an allergy to it in more recent years. So what I really want to know is why people can become allergic to things over time. How is our body not tricked by harmless things, but then forgets how to handle them later?

[Curtistopsidae]

Worth mentioning that the type of allergy from urushiol is different than the classic food allergy. It's a type IV hypersensitivity reaction which tends to only cause symptoms after 12+ hr vs most food allergies which are type I hypersensitivity reactions and cause symptoms within the hour

[ABCD-rmvo]

Fun fact, urushiol can also be found in the skin of mango and the shells of pistachios and cashews.

[princetandukar]

I love how pickachu is eating poison ivy 2:11

[AverytheCubanAmerican]

When poison ivy isn't actually poisonous at all:
*So that was a F'ing lie*

[sciencenerd]

The summer before kindergarten I had a real bad interaction with poison oak. Later at school, when asked about allergies, I told kids that "I'm allergic to poison oak". Other kids said, no, you're dumb, that is not an allergy because everyone reacts to poison oak. Today I found out that I was right all along!

[emperium]

Huh, I always assumed everyone would be adversely affected by poison ivy. Interesting to know it has no effect on some people.

[ThatCatLover]

Urushiol affects more adults then children, because most people who are born without an allergie for urushiol develop it as they get older.

[yotammor]

I am happy that i understand allergys now

[scaboodle]

This video is a little misleading. At 1:22 you say this is the same phenomenon as other allergies. This isn't true as other allergies are IgE mediated (i.e. caused by antibodies and generally only in reaction to proteins!) and known as type I hypersensitivity. The process you have described for urushiol is a type IV hypersensitivity. Which is arguably not an allergy at all!

[johnsteinat]

I wonder if there could be a related benefit that we would lose if we lost that allergy. If it only affects the primates most closely related to us and the rate is so high, it seems like that's only possible if not having the allergy was detramental to the point of almost destroying the gene. Or maybe, because poison ivy grows in North America and Humans evolved in Africa, it's just coincidence, like lacking the ability to make vitamin C

[JesusMartinez-rrry]

I chuckled when you also included Bigfoot as one of humans' close relatives who are also allergic to the urushiol in "poison" ivy.

[cruros]

Ironically just learned about this type VI hypersensitivity in my immunology class a few weeks ago.

[Darknimbus]

Actually urushiol in high quantities, such as found in the cashew shell (cashew is in the poison ivy family btw), can be very toxic. It’s why you never see cashews with the shell on in the market, and why “raw cashews” aren’t actually raw (in the culinary sense).

[cinnamonsugarcourtney]

I'm not allergic to urushiol. :3 I've never had an outbreak due to it... but my brother and little sister are very allergic to it. I know because I was leading a walk with my sister and she walked after me and by the time our walk was over she had broken out due to poison ivy, but even though I was wearing shorter pants and things nothing happened to me. We were going the same path and she was right behind me, not next to or anything.