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

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

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

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

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

And, you can develop new allergies.

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

A shrimp can kill you.

How bizarre.

But like, what are allergies?

Why do our bodies flip the table on harmless stuff?

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

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

This is very upsetting and interesting.

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

We won't get into the disgusting details, but in a world where drinking water and our poo were close buddies, some species of worms found just the perfect cycle of life.

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

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

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

This caused all kinds of unpleasant health effects.

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

But how do you do that?

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

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

You really need to pack some punch to cause damage.

It takes an army to kill a worm.

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

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

We explain them in detail in this video.

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

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

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

An army of really scary cells called mast cells.

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

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

And then, they just lie and wait, angrily.

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

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

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

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

They release all of their dangerous chemicals all at once.

A few things now happen in rapid succession.

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

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

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

Other chemicals are like air raid sirens screaming loudly throughout your body for anti-parasite soldiers.

Eosinophils.

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

Not 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.

Sometimes, this will straight up kill the parasite.

Lastly, the anti-worm coordination cell arrives.

The basophil.

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

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

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

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

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

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

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

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

What is an allergy?

Parasitic 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.

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

They 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 everyday.

Our ancestors were basically unable to prevent regular worm infections.

So, as the worms adapted to us, our bodies had to adapt to them.

To 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.

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

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

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

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

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

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

It 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.

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

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

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

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

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

So 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.

Until one day, you eat another shrimp.

Your anti-parasite forces flip on like a switch.

Only, there is no kaiju to attack.

This is what you experience when you have an allergic reaction.

Extremely powerful weapons now target your own body.

Under your skin, your blood vessels suddenly turn leaky.

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

You immediately feel hot and unwell.

In your digestive system, the mast cells can cause nausea, cramps and sharp pain, as water floods into your intestines and triggers intense diarrhea and vomiting.

Your respiratory tract swells up, making breathing hard.

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

In the best case, you get a stuffy nose.

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

Mast cells all over your body unload their bombs all at once, causing an anaphylactic shock.

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

This alone is life-threatening.

In combination with the things going on in your lungs, anaphylaxis is a life-or-death emergency, often with just a small time window to do anything about it.

Allergic reactions truly are no joke.

Even the deadliest diseases like Ebola need days to kill you, but your immune system can kill you within a few minutes.

And this is why a shrimp can kill you.

Because on a fundamental level, an ingenious defense system, vital for our species' survival for millions of years, is fighting imaginary kaijus.

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

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

And we're not sure if the lack of worms is the main culprit, only that the cells that evolved to fight them are responsible for the symptoms of allergies.

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

Maybe it's just a combination of all of them.

But what we clearly see is that allergies and their more serious cousin autoimmune diseases have been rising massively in the last 100 years.

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

Hopefully, we'll figure it out and prevent allergies forever, because one thing's for sure, we don't want to get worms back.

That would really be like finding a spider and exploding a nuclear bomb.

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It took us 10 months to create this latest edition of our annual passion project.

The fact that we're finally able to share it with you is truly our highlight of this crazy year.

It's the 12,025 Human Era Calendar, and it's the best calendar we've ever made.

It all started back in January.

While we released the first video of the year, we were already brainstorming ideas for the 12,025 calendar.

For years, we'd wanted to tell the story of the great journey that took our ancestors from Africa to find new homes across the planet.

We dove headfirst into research.

We read about curious and unbelievably brave humans who ventured out into the unknown, paving the way for future generations.

But all of these incredible stories had to fit on paper, on 12 pages no less.

Weeks of sketching and revisions followed in February.

What was it like for those early pioneers?

Every new terrain they explored must have appeared to them like an alien planet, ruled by unfamiliar climates and filled with foreign creatures.

Meanwhile, we released our next videos, and in March were finally able to tell you about Starbirds, the video game we're working on with Tucana Interactive.

Then the calendar came to life.

We spent many weeks crafting epic illustrations worthy of representing 200,000 years of human history.

We had to get it right.

The adventures, the hardship, the incredible achievements.

We don't know what our ancestors set out to find, but when they settled all across the planet, they laid the foundation for human civilization.

Then, in May, Smoking is Awesome became our most successful video this year.

It had a huge impact and inspired many of you to quit smoking for good.

Nothing could make us happier.

Back in the studio, we created the final piece of the calendar, the cover.

As always, we wanted to represent the entirety of the human era by adding 10,000 years to the common era system.

Adding that one was the final touch, and our calendar was ready to be sent off to the printer.

On our YouTube channel, we continue to ask the big questions like, do you have free will?

And is AI humanity's final invention?

Then, in September, we finally held the first copy of the finished 12,025 calendar in our hands.

We are truly happy with the result.

It's not just the vibrant illustrations, the high-quality paper, or the shiny cover.

It's the fact that it represents such an important part of our shared human history.

And, for us, it holds all the memories of an exciting year at Kurzgesagt.

We think it's the best product we've ever made.

We may be a tiny bit biased, but you birbs seem to love it too.

It's absolutely incredible to see all your comments and messages.

For so many of you, getting the human era calendar has become a yearly tradition and a daily source of inspiration.

Make 12,025 truly special.

Get your piece of our shared human history and an essential part of Kurzgesagt.

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