How Do Allergies Work?

Chances are, a good amount of the people reading this have had an allergic reaction to something on Earth. More than 50 million Americans suffer from allergies every year. But how do these allergies work and what makes them one of the most common chronic diseases? The simple answer is a confusion in the immune system but it is also much more complicated than that.

An IgE antibody

To start an allergic reaction, the person needs to come into contact with the allergen. It is possible to be allergic to just about anything, from medicine to foods and anything in between. Once the allergen is inhaled, ingested, or enters the body in any way the person's immune system sees this substance as dangerous and attacks it with immunoglobulin E (IgE) antibodies. IgE antibodies can only bind to one type of allergen. That means that there are a ton of variations and each one is made specifically for a certain allergen. That's why it is possible to be allergic to one type of pollen but not another. Every person's body only creates IgE antibodies for allergens that they are allergic to.

Allergens binding to antibodies to release histamines

The antibodies act as cell receptors so once they bind with the allergen they prompt the cell to release histamines across the body. Histamines are one of the human body's defense systems. They are organic molecules based on the structure of ammonia that bind to other receptors and other cells in order to trigger a response. Since the immune system sees the allergen as a dangerous substance, it is going to do all that it can to try to get it out of the body. Histamines are the direct cause of reactions like coughing, itching, and sneezing because they send the cells and tissues signals to perform that function after they bind to them. Coughing forces substances out of the mouth and sneezing forces substances out of the nose. The more histamines released, the worse the allergy symptoms get. Once there are no more allergens in the body, the antibodies do not get bound to and histamines stop being produced.

Signal transduction pathway of epinephrine

Anaphylaxis, or anaphylactic shock, is a severe allergic reaction. These can sometimes be life threatening and are usually caused by severe allergies to food or medication. In these cases the body overproduces a ton of histamines and other chemicals which create very drastic allergic reactions and symptoms. Some of the symptoms can compromise the respiratory system which leads to cardiovascular compromise and respiratory compromise which are fatal. The heart is also weakened and if it cannot pump enough blood throughout the body that can be fatal too. EpiPens are often used when anaphylactic shock occurs because they help reverse the negative effects. They release the hormone epinephrine which quickly relaxes muscles in the airways, stomach, intestines, and bladder. It also reverses the rapid decrease in blood pressure that anaphylactic shock usually creates. As shown above, the epinephrine that is injected binds to cells and goes through a signal transduction pathway that eventually leads to glucose being produced. One of the main effects that glucose can have is increased heart blood flow which can help combat anaphylaxis. 

Diagram showing how antihistamines block the histamine receptors

The way to treat less severe allergies is through antihistamine medication. Instead of stopping the symptoms, like EpiPens, they stop the cause of the symptoms. Antihistamines are designed to bind to the histamine receptors but when they bind they do not prompt any signals to be sent. Since the site is active and the antihistamine is physically bound to the receptor, the histamines that are released have nowhere to bind. This effectively stops the allergy symptoms from occurring.

Some popular antihistamine brands

I choose to write about allergies because I have seasonal allergies and wanted to know more about how they work. I found it interesting that one person's favorite food could be deadly to another person and it is all dictated and started by antibodies. Whether it's food, medication, or anything else, it is common to have some kind of allergy. Despite the effects that we get when we react to an allergen, allergens are not harmful by themselves. If the immune system didn't mislabel them as dangerous, they would be completely harmless. So instead of blaming the allergen the only thing we can blame is the immune system. And possibly your parents too as allergies can sometimes be hereditary. The good thing to take away from this is that it might not even matter in a while, since there is a decent chance that allergies can be outgrown. This claim is largely dependent on the allergy as studies have shown that allergies like tree nuts and shellfish are usually lifelong. Everybody's body is different though, and one way to loosely predict if an allergy can be outgrown is testing the level of IgE antibodies specific to that allergen that are present in the body. If the allergy is not outgrown it is not all bad, the best treatments are to avoid exposure to the allergen and seek medical help or take antihistamines you are exposed. That is well worth it to save yourself possible severe allergic reactions.