The Real Reason Why You Have Allergies

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Transcript

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00:31An allergy is like finding a spider in your bedroom and exploding a nuclear bomb.

00:36Sure, spiders are upsetting and now dead, but so are all of your neighbors and your dog.

00:42You can be allergic to an incredibly diverse and weird amount of stuff.

00:46Pollen, dust, insect stings, animal hair, any kind of food, latex and even your own sweat.

00:53One of the wildest things about allergies is how fast they are, breaking out suddenly and violently.

00:59And you can develop new allergies.

01:01One moment you're enjoying a shellfish you ate thousands of times before, and the next moment you wake up in an ambulance.

01:07A shrimp can kill you. How bizarre.

01:10But like, what are allergies? Why do our bodies flip the table on harmless stuff?

01:16There's a wild and interesting idea we want to share with you.

01:19Humans might have created allergies by accident, by getting rid of worms.

01:25This is very upsetting and interesting.

01:28For your ancestors, being infected by worms was a reality of life.

01:32We won't get into the disgusting details, but in a world where drinking water and our poo were close buddies,

01:39some species of worms found just the perfect cycle of life.

01:43They enter your bodies with the water and make themselves at home, sometimes for decades.

01:48And then release their eggs or larvae with your poo, which used to go back to the water we drank.

01:54So, until recently, in evolutionary terms, our ancestors had to deal with frequent or permanent worm infections.

02:00This caused all kinds of unpleasant health effects.

02:04Our immune systems had to find weapons to get rid of them.

02:07But how do you do that?

02:09From the perspective of a cell, worms are city-scale kaijus, reaching beyond the horizon.

02:15Worse, instead of skin, parasitic worms have an elastic protective layer that withstands even stomach acid.

02:22You really need to pack some punch to cause damage. It takes an army to kill a worm.

02:27We're simplifying, but basically, when a worm enters your body for the first time, intelligent cells notice their presence.

02:34They move to your lymph nodes and activate specialized antibody factories called B-cells.

02:38We explain them in detail in this video.

02:41These B-cells are told that they need to fight parasites and start producing a special class of weapons, IgE antibodies.

02:49Tiny protein craps with two pincers that connect to worms like magnets to metal.

02:54IgE floods your entire body and basically begin arming a nuclear bomb.

02:59An army of really scary cells called mast cells.

03:03Mast cells are huge, bloated fellows filled to the brink with histamine and other nasty chemicals.

03:09They pick up the IgE floating around and cover themselves with them like angry hedgehog grenades without their safety pins.

03:16And then, they just lie and wait, angrily.

03:20So now, you have millions of bombs in your skin, lungs, or gut.

03:25Until the day the mast cells meet a worm trying to enter your body.

03:30There's not much time to get rid of it, so things escalate rapidly.

03:34The mast cells with their IgE spikes grab onto the worm particles and kind of explode.

03:40They release all of their dangerous chemicals all at once.

03:43A few things now happen in rapid succession.

03:46First, some of the mast cell chemicals wound the worms, ripping wounds into them and making them really unhappy.

03:52Then, emergency chemicals like histamine cause massive and rapid inflammation, ordering your blood vessels to flood the battlefield with water to flush the worms out.

04:01They also order your cells that make mucus to go into overdrive and cover the worms in sticky slime.

04:07Other chemicals are like air raid sirens screaming loudly throughout your body for anti-parasite soldiers, eosinophils.

04:14First thousands, then hundreds of thousands hear the alarm and leave your blood vessels to where the mast cells are causing inflammation.

04:22Not only do they make the inflammation worse, they carry extremely toxic chemicals that they vomit at the worm, ripping open its defensive layers and causing horrible injuries.

04:32Sometimes, this will straight up kill the parasite.

04:36Lastly, the anti-worm coordination cell arrives, the basophil.

04:40It makes sure that the immune system doesn't slow down, but keeps attacking with violence.

04:45It keeps the inflammation going and alerts more and more attack cells to the site of battle.

04:50Zooming out, we see that the chemicals from your anti-parasite forces make your smooth muscles contract rapidly, pushing everything that's inside outside.

04:59In your intestines, combined with all the water, you notice this as diarrhea, as your body tries to expel the stressed parasite.

05:06In your respiratory tract, loads of mucus and water flood outside, trying to take the worm with them.

05:12If this happens under your skin, your tissue is red, hot and itchy, as your immune system is trying to commit murder.

05:19It takes a fierce army to kill a worm, and your anti-parasite forces have the license to act rapidly and with intense violence.

05:28Okay, this is nice and all, but what does all this have to do with killer shrimps?

05:33What is an allergy?

05:35Parasitic worms don't love being ripped apart by millions of bombs, and as all living things do, they adapt it to the deadly attacks on them.

05:43In a nutshell, worms release a plethora of chemicals to manipulate your immune system.

05:49They make it weaker and much less angry, like immune system weed, which is pretty bad for your survival because you have to fight off all sorts of intruders every day.

05:58Our ancestors were basically unable to prevent regular worm infections, so as the worms adapted to us, our bodies had to adapt to them.

06:07To balance out any weakening worm chemicals, one adaptation might have been to make our immune system more aggressive so it could still defend against other invaders.

06:16And then a hot second ago, in evolutionary terms, everything changed.

06:20We suddenly invented soap and hygiene, but most importantly, the separation of poop and drinking water.

06:27This destroyed the life cycles of parasitic worms, and the ones that remained were eradicated by modern medicine.

06:34Worms still infect up to 2 billion people, mostly in underdeveloped rural regions or slums with unsanitary conditions and dirty water.

06:42The people who escaped these conditions now face an interesting problem.

06:46An immune system without a major enemy that had kept it down for millions of years.

06:51It could very well be that our immune system still operates assuming that worms are making it weaker, and that it has to be overly aggressive because of that.

07:00And while IgE, mast cells, basophils and eosinophils also have other jobs, a major reason for their existence has now gone away.

07:10But they kind of act as if worms are around, only that they now attack other dangerous foes, like shrimps.

07:17This is exactly what happens when you have an allergic reaction to a shrimp.

07:21Your immune system picks up shrimp proteins and produces IgE antibodies against shrimps.

07:27The antibodies then are mast cells, turning them into bombs.

07:31So you have millions of bombs in your skin, your lungs or your gut, with a license to choose violence even when provoked a little bit.

07:39Until one day, you eat another shrimp.

07:42Your anti-parasite forces flip on like a switch.

07:45Only, there is no kaiju to attack.

07:48This is what you experience when you have an allergic reaction.

07:51Extremely powerful weapons now target your own body.

07:55Under your skin, your blood vessels suddenly turn leaky.

07:58Fluid streams into your tissue, your skin swells up and turns red, often in itchy hives.

08:04You immediately feel hot and unwell.

08:06In your digestive system, the mast cells can cause nausea, cramps and sharp pain,

08:11as water floods into your intestines and triggers intense diarrhea and vomiting.

08:15Your respiratory tract swells up, making breathing hard.

08:19Way more dangerously, histamine and other chemicals can cause the smooth muscles in your lungs to tense up.

08:25In the best case, you get a stuffy nose.

08:28In the worst case, you're suddenly fighting for your life.

08:32Mast cells all over your body unload their bonds all at once, causing an anaphylactic shock.

08:38Your blood loses so much water that your blood pressure drops to dangerous levels.

08:43This alone is life-threatening.

08:45In combination with the things going on in your lungs, anaphylaxis is a life-or-death emergency,

08:51often with just a small time window to do anything about it.

08:54Allergic reactions truly are no joke.

08:57Even the deadliest diseases like Ebola need days to kill you,

09:00but your immune system can kill you within a few minutes.

09:03And this is why a shrimp can kill you.

09:06Because on a fundamental level, an ingenious defense system,

09:09vital for our species' survival for millions of years, is fighting imaginary kaijus.

09:15Yet we still don't know why some people produce a lot of IgE antibodies against certain substances, and others don't.

09:22We don't know why some adults develop new allergies later in life, or why some allergies disappear over time.

09:28And we're not sure if the lack of worms is the main culprit,

09:32only that the cells that evolved to fight them are responsible for the symptoms of allergies.

09:37There are other ideas, like less diverse microbiomes or increased pollution.

09:42Maybe it's just a combination of all of them.

09:45But what we clearly see is that allergies and their more serious cousin, autoimmune diseases,

09:50have been rising massively in the last 100 years.

09:53Wherever, humans moved into more sanitary conditions and got rid of some of the horrible parasites hunting us.

09:59Hopefully, we'll figure it out and prevent allergies forever,

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