When you picture allergies, you may imagine someone sneezing, coughing, and itching on

a beautiful spring day.

Or perhaps you think of someone accidentally eating peanuts or shellfish and going into

anaphylactic shock.

Whatever the case may be, allergies are a serious problem for many millions of people.

But how and why do they develop?

And what's so different between allergies to pollen or dust and allergies to bee stings

or soy?

Well, let's start with what these different types of allergies have in common: your immune

system.

When an allergen makes contact with a surface on or in your body, nearby immune cells act

quickly to destroy the allergen.

The cell then covers itself in broken pieces of the allergen and moves to a site of some

lymph tissue.

When it gets there, it passes pieces of the allergen onto even more immune cells, so that

they can work together to form an antibody called immunoglobulin E.

If the body comes into contact with the allergen again, these antibodies—which are proteins

designed to attach to foreign substances and remove them from your body—will start a

reaction to fight against it.

First they activate a part of the immune system called a mast cell, which then expels a lot

of chemicals, like histamines.

When histamines are released, they make your capillaries—the smallest blood vessels in

your body—more permeable, which allows white blood cells to enter the capillaries and fight

the allergens.

However, increased permeability doesn't just let white blood cells in.

It also lets fluids out, causing the watery eyes and runny nose that you know and love.

And similarly, a congested nose is caused by the capillaries growing larger due to the

increased permeability.

So that covers how you get allergies.

But what about why?

Why would your body turn against itself like that?

And why are some allergies just annoying while others are deadly?

For many years the prevailing idea was that the immune system perceived allergens as being

similar to parasitic worms, and for that reason it would unleash the same attack on a peanut

as it would on a tapeworm.

Parasitic worms are a serious threat, but they are less prevalent than they were in

the lives of our ancestors, which explains why Immunoglobulin E would choose to attack

allergens in the absence of worms.

A similar theory says that allergens may have posed a real threat to us many years ago.

According to Dr. Kate Welch, a specialist in immunology and allergies, it's possible

that our ancestors were in serious danger when they encountered something like pollen.

Therefore, our immune systems are kicked into gear when they make contact with these allergens,

even though we evolved and pollen isn't a big threat anymore.

Welch claims that it's even possible that allergic reactions are important because they

may warn us to get out of a dangerous area, say, directly under a wasp nest.

Finally, another theory has come to light recently, and it claims that allergens are

actually more dangerous than we might have known.

Researchers Ruslan Medzhitov, Noah Palm, and Rachel Rosenstein are at the forefront of

allergy research, and they've embraced the new theory.

They conducted a study in which they injected mice with an allergen found in bee venom called

PLA2, which rips cell membranes apart.

They found that immunoglobulin E didn't react to the PLA2—until it started hurting

cells.

So when you cough or your nose runs, this study suggests that it's just because your

immune system is trying to get dangerous allergens out of your body!

And when it comes to life-threatening allergies, they're simply a more overactive version

of the same response.

So don't let your sneezing bother you too much!

Your immune system is doing you a big favor.

Make sure to come back every Monday for a brand new video.

As always, my name is Blocko and this has been Life Noggin.

Don't forget to keep on thinking!