Each year, 26 million Americans experience allergies, sometimes nicknamed hay fever.

When trees, weeds, and grasses want to mate, they release thousands of pollen grains into the air — which can end up entering your lungs, eyes, and nose.

Special antibodies attach to the grains and summon immune cells to the scene.

These release histamine chemicals, which irritate your nose, causing you to sneeze the pollen out. Histamine also causes you to produce more mucus, which helps flush out the grains.

Climate change is causing plants to release more pollen, for longer periods of time. So allergies are getting worse than ever.

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Following is the transcript of the video.

Narrator: When trees, weeds, and grasses mate, they make a mess. Thousands of pollen grains — their reproductive material — fly into the air. And anyone with allergies knows not to get too close, or else. But what is it about that fluffy stuff that sets off the summer sneezes, anyway?

Each year, 26 million Americans experience an allergic reaction sometimes nicknamed hay fever. The culprit? Pollen. And to help them get to where they need to go, the pollen grains are extremely light and sticky. The wind can carry them for thousands of kilometers across state lines and over mountains.

You can even find pollen over 600 kilometers out to sea, with no trees in sight. In other words, this sticky stuff gets everywhere. And sometimes it sticks to places it shouldn't. Like your clothes, car, and especially your eyes, nose, and lungs. That's when the trouble starts.

But here's the odd thing about pollen. On its own, it's harmless. It's not a virus or parasite that can give you a disease or damage your organs. It only becomes a problem when your body sees it as one.

Dr. Todd Mahr: "Our body reacts to that antigen—basically the protein in the pollen, and for some reason our body recognizes it as foreign."

Your immune system has a merciless procedure for dealing with intruders. The first line of defense are Y-shaped proteins called antibodies. They're like a built-in security system that guards your nose, eyes, and mouth, along with other tissues. When they bump into a grain of pollen, they sound the alarm.

Now, their main goal is to get that pollen out of your system. Which they do by sending a rush of white blood cells to the scene which then produce a chemical called histamine. Histamine has a few ways to get the job done: First, it irritates your nose, forcing you to sneeze.

Which blasts some of the pollen away! Second, it expands your blood vessels, opening tiny gaps between the cells that make up the wall. Opening the path for a squadron of immune cells to squeeze out and attack the pollen grains.

Finally, it tells your nose to make more mucus! Which traps the invader and flushes it out of your nasal passages. Mission accomplished. Histamine also flushes out your eyes in a similar way. It irritates your eyes, causing them to swell and tear up. And if pollen reaches your lungs, histamine irritates the lining, causing you to cough it out.

The end result? You're a snotty, miserable mess. And since different plants reproduce at different times in the spring and summer, the assault can last for months. But, hey, at least your system is pollen-free. Now, pollen isn't the only irritant that can cause this type of reaction.

Dr. Todd Mahr: "People react to foods, they react to pollens, they react to chemicals, they react to antibiotics, they react to bee stings. All of those are the same type of immune reaction."

However, pollen is one of the most common allergies, but scientists aren't entirely sure why. What they do know is that some people have more sensitive immune systems than others. And that's based on a bunch of factors, like genetics, when you were first exposed to pollen, and how much of it you were exposed to.

Dr. Todd Mahr: "All of that influences what your body's going to do and what kind of reaction it's going to have."

Regardless of how you ended up with allergies, one thing's clear: THEY SUCK.

Dr. Todd Mahr: "You're going to be really miserable. And some people are very, very uncomfortable, and it leads to lost work, to lost school."

Seasonal allergies cost the US $18 billion a year in lost work hours and medical bills. And there's bad news: Climate change is making them even worse. A recent series of studies showed that over the past 20 years as global temperatures have climbed, pollen counts have risen with them.

Plus, the earlier and longer periods of warm weather have stretched prime pollen season longer than ever.

Dr. Todd Mahr: "If it's warmer, which is what climate change is doing, you're going to have more of those pollinating species thriving."

The good news is, there are ways to keep the summer sneezes at bay. Like antihistamines. These meds grab on to those irritating histamine molecules, preventing them from working. Hence the name ANTI-histamine.

So as the skies cloud with yellow horror dust, and pollen counts skyrocket, grab a tissue, pop an antihistamine, and hope that winter returns soon.

EDITOR'S NOTE: This video was originally published in August 2019.