Allergy is a broad term to describe certain types of symptoms that people experience due to changes in their immune system. The body’s immune system is typically very good at figuring out what is foreign like viruses or bacteria so it can get rid of them. Also, the body is supposed to be able to allow non-harmful foreign molecules from foods, pollens, and other allergens and not react. However, sometimes the body senses these proteins and does react in people with allergies.
In an allergic reaction, parts of the immune system make and release histamine and other molecules. Generally, allergies in the nose and eye cause symptoms like congestion, itching, fluid production/swelling, and sneezing. In the skin, hives and swelling/edema can occur. In the stomach and gastrointestinal tract, people can have nausea, vomiting, diarrhea, and cramping. When allergy is in the lungs, patients report coughing, wheezing, and trouble breathing.