How Allergies Work
What Happens During a Histamine Reaction?
Why can some people eat peanuts while others may die from the smallest amount? Why are bee stings a minor annoyance for some yet a death sentence for others? It all comes down to your immune system. While the immune system can be likened to a fortified castle filled with knights, archers, and weaponry, occasionally these knights mistake a harmless villager for an enemy spy and wage an unnecessary war.
There are four types of allergies but type 1 is what usually comes to mind when allergies are considered. Type 1 allergic reactions are also named IgE immune responses. IgE, or immunoglobulin E, is a protein that the body makes when triggered by an allergen. The IgE molecules bind to the allergen molecules, then signal the body to release other chemicals including histamine. Histamine is what causes you to be miserable by actively working to get the allergen out of the body. For airborne allergens, this is typically done through sneezing, coughing, runny nose, and watery eyes. For ingested allergies, the digestive tract may work to expel the allergen either by vomiting it back up or making it pass through the body abnormally quickly (with many trips to the bathroom).
As we explore the type 1 allergies more, let’s apply it to something we all know: bee stings. In any given person, a bee sting will hurt, itch, and swell. This is temporary, inconvenient, and essentially harmless. However, if you were to develop a bee allergy, this would be a different story. The first time you got stung, you might not have much reaction beyond the norm. However, that first sting will cause a sensitizing reaction. When the bee venom enters your body, your B cells (a type of white blood cell that makes antibodies) kicks into gear making IgE specifically targeting the bee sting venom. Those IgE antibodies travel throughout your body and bind to mast cells. Mast cells are like the armory of the castle, just with histamines and other inflammatory chemicals instead of arrows and swords. When an IgE antibody binds to that mast cell, it prepares for a fast reaction the next time the new allergen (bee venom) enters the body.
With a primed armory (your mast cells), your body is ready to launch an all-out war with the next bee sting you receive. When the bee venom is detected, your mast cells dump out the entire armory of histamine, cytokines, and plenty more. Histamine causes inflammation. This triggers small blood vessels to leak, causing swelling. It makes mucus membranes produce more mucus. It even stimulates a special type of nerve whose sole purpose is to make us feel itchy. It may cause smooth muscle to contract, such as bronchial muscles tightening in the throat. Mast cells are found most in the areas where you feel reactions: skin, respiratory tract, digestive tract, near blood vessels and lymphatic vessels, and around nerves.
We may not realize, but these allergic reactions come in two phases, and I have only described the first, or immediate phase. The second phase occurs several hours later when white blood cells are brought to the affected area causing swelling, pain, warmth, and redness. In the lungs it increases the production of mucus. This phase takes a few days to end.
Anaphylactic shock, or anaphylaxis, is a dangerous reaction that causes your airways to narrow and blood pressure to drop rapidly. This is also due to the mast cell mass ejection of chemicals, but throughout the entire body rather than localized. With blood vessels throughout the body leaking into the surrounding tissues, up to 50% of your blood may leave the blood vessels. This is the cause of both the blood pressure drop and the severe swelling. When throat tissues swell rapidly, it can be very difficult to breathe, not to mention the potential spasms in the airway. With low blood pressure and now less oxygen entering the body, the brain becomes starved for oxygen. When suffering from anaphylaxis, a shot of epinephrine (adrenaline) can relax the airways and blood vessels, but hospital care is still necessary afterwards.
When it comes to allergy severity, “mild” allergies do not exist. You are either allergic or you aren’t. It is the reaction that ranges from mild to severe. Allergy reactions are unpredictable. Having a mild reaction one time doesn’t guarantee a mild reaction next time and vice versa with having a severe reaction. Many factors affect the severity of the reaction including how much allergen you are exposed to, if you are taking certain medications, have alcohol in your system, or if you have recently exercised. An allergic reaction that is severe or occurs in multiple body parts or systems is more likely to become anaphylaxis.
We do not fully understand why some people develop allergies, but we do know that they have a genetic component and run in families. This is also true of the other types of allergens. Type 2 allergies are caused by IgG and IgM antibodies targeting certain cells of the body. This can cause some conditions such as Graves’ disease (thyroid-stimulating hormone), immune thrombocytopenia (white blood cells), and autoimmune hemolytic anemia (red blood cells). It can even be observed in blood transfusions if the ABO blood types are not compatible, with the immune cells of the person receiving the transfusion attacking the new red blood cells en masse.
Type 3 allergies happen when excess antigen is not cleared from the body and bind up antibodies forming small immune complexes. White blood cells have difficulty getting rid of these small complexes, allowing them to insert themselves into small blood vessels, joints, and other areas causing damage and inflammation. This reaction can take hours, days, or weeks to develop conditions such as Rheumatoid arthritis, Systemic lupus erythematosus, serum sickness, or reactive arthritis.
Type 4 allergies are delayed reactions caused after at least 24 hours of exposure to the allergen. It is within the cell rather than antibody mediated. This could be an allergy to certain metals. It is also seen in tuberculosis and some fungal infections.
Roughly half of the population of the United States has at least one allergy. Hay fever alone affects 10-30% of adults. The percentage of allergies has been increasing significantly in the past few decades. As wonderful as our bodies are, they do make mistakes and allergic reactions are one of them.
Allergies Statistics and Facts. (2012, May 4). Retrieved from Healthline: https://www.healthline.com/health/allergies/statistics#Age,-Gender-and-Other-Factors
Catherine Carver, M. (2017). Immune. Croydon: Bloomsbury Publishing.
Originally published in the February/March 2022 issue of Backyard Beekeeping and regularly vetted for accuracy.