Why Are Allergies So Common?

Hey there, everyone. Welcome back to Seeker Plus, where we go in-depth on the topics that fascinate, bemuse, and amuse us. I'm your host, Julian, and where I am in North America, spring is here. The birds are chirping, the flowers are blooming, the seasonal allergy sufferers are miserable. About seven to eight percent of people in the U.S. suffer from hay fever, and for many of them, right about now is the start of the bad times. They're bracing for an onslaught of symptoms like constantly runny noses, red itchy eyes, fatigue, and sneeze after sneeze after sneeze. Who knew that plants could be practically murderous? Aside from Mark Wahlberg in that one weird M. Night Shyamalan movie, The Happening, you know the one I mean? Still, hay fever is just one variety of allergies. People can be allergic to certain foods, or medicines, or insect stings, or animals. Some allergic reactions can do more than make the sufferer for the sweet embrace of death. It can actually kill them. So, be careful what you wish for. In this Seeker Plus, we wanted to take a look at allergies. What's happening in the body that causes this reaction? Why do some people have allergies, while others get to live blissfully clear-headed lives? And how do allergy treatments work? When looking at the variety of things that cause allergic reactions, and how wildly different the reactions can be, I started to wonder why they all fit under the umbrella of allergies. Well, it turns out it's because the definition of an allergy is pretty broad. Allergic reactions happen when the body's immune system overreacts to something that's normally harmless. These substances are called allergens. For people with allergies, their first exposure to an allergen may be harmless. On the inside, their body is ringing alarm bells and gearing up for future invaders. Days or even years can pass between the first exposure and the first allergic response. Really, you never know if you have an allergy and just don't know it yet. Which is something that we'll talk about later. Some people may seem as though their bodies are reacting the very first time they're exposed to an allergen, but they may have unknowingly encountered it before, through their skin, or when they were babies being breastfed, or even in the womb. But for their immune system to respond, it must have had a run-in with this perceived threat before. After that initial encounter, a person with allergies will start producing more of a specific antibody inside their body. Now, to be clear, antibodies are incredibly useful parts of your immune system. They're little Y-shaped proteins that are part of your body's adaptive immune system, which can learn to recognize new threats and destroy them. Antibodies are also known as immunoglobulins, and humans have five varieties, IgG, IgA, IgM, IgD, and IgE. While they all have that Y-shape in some arrangement or another, their exact structures differ, and they're found in different parts of the body and have different roles and functions. IgG are the smallest and most common, making up about 75% of your antibodies. They help fight viruses and bacteria, and they can give developing fetuses an immune boost from their birthing parent while in the womb. IgA are found in serum, as well as spit, sweat, and tears, and they're also in the gastrointestinal, respiratory, and genitourinary tracts. IgM are the first antibodies made when an infection is detected, and we're not totally sure what IgD do. Finally, there's IgE, and these are the jerks responsible for a lot of allergic reactions. Now, normally, when something harmful enters your body, it's detected by a type of white blood cell known as B-cells. You have about a trillion B-cells in your body, and because of genetic shuffling, each one has a different IgM antibody on its surface that reacts to a specific intruder. If a B-cell's antibodies bind to something, the B-cell starts dividing and creating a clone army, much like Count Dooku. There can be millions of cloned B-cells, which transform into plasma cells that pump out antibodies at a prodigious rate. Each plasma cell can produce as many as 10,000 antibodies every second. These antibodies swarm invaders and can either neutralize them directly or tell other cells in the immune system to come take out the trash. Anything that makes your immune system generate antibodies is called an antigen. Get it? An-tee-gen? For people with allergies, the trouble starts when B-cells that are supposed to make IgM antibodies start making IgE antibodies instead. Certain antigens, and certain ways antigens make contact with the immune system, increase the likelihood of switching to IgE production. These IgE antibodies are still sensitive to that antigen, and on top of that they bind to other cells, like mast cells and basophils. When IgE binds to both an antigen and these other cells, it can trigger the creation of even more IgE from B-cells. Mast cells and basophils can also release inflammatory mediators, including histamine, and this is the last domino to fall in this long sequence of cascading misery. Histamine increases blood flow to wherever the allergen is, and then dock with receptors that cause symptoms allergy sufferers know all too well. In the nose, it causes mucus production, it leads to itchy red eyes. In your skin, it can cause hives or eczema. In the gut, it can cause vomiting and diarrhea. All of these symptoms really have the same goal. Get whatever the IgE is reacting to out of your body. If histamine has to make you blow your nose, or scratch like mad, or retch up your lunch, so be it. Histamine, along with other substances released by mast cells and basophils, can cause more than just discomfort. In some cases, the effects can combine dropping blood pressure, speeding up heart rate, and constricting airways. This full body rapid meltdown is known as anaphylaxis, and if not treated quickly, the results can be deadly. So, what gives, IgE? What exactly was your whole plan here? Well, like many things that lead to horrible consequences, it all started with good intentions. IgE antibodies are specialized at fighting parasites. They came in handy back in the early days of humanity, when we encountered parasites regularly. In fact, they were probably necessary for our survival, and still are for people who live where parasites are more common. But without a serious foe, IgE antibodies are like that high-strung dude at a bar who's just looking for an excuse to fight anybody. Sometimes, that happens to be cat dander. I mean, you could count cats as parasites. They do eat your food, and they give you almost nothing in return. I'm kidding, cat owners. I have a cat who I love, even though I am allergic to cats. If that's not love, I don't know what is. And besides, people are allergic to dogs, too. So, why is that? Why are some people allergic to certain animals or foods, while others aren't? We'll get into that in our next episode. For now, I hope you enjoyed this topic, especially if you're an allergy sufferer like me, who wishes they could just explain to their immune system that everything's chill. You don't need to go so hard. Let me know if you're in the puffy-eyed gang, or if you're not, and you think you're just so much better than us, because I have news for you. You might be joining us at some point. Yeah. Yeah. Who's laughing now? And sneezing. And rubbing their eyes. All right. That's it for me. I'll see you on the next episode of Seeker Plus.