The substances that set off an allergic reaction are called triggers or allergens. An allergic reaction involves two features of the human immune response. One is the production of immunoglobulin E (IgE), a type of protein called an antibody that circulates through the blood. The other is the mast cell, a specific cell that occurs in all body tissues but is especially common in areas of the body that are typical sites of allergic reactions, including the nose and throat, lungs, skin and gastrointestinal tract.
Before an allergic reaction can occur, a person who is predisposed to form IgE to the trigger first has to be exposed to it. As this trigger is encountered, it causes certain cells to produce specific IgE in large amounts. The IgE is then released and attaches to the surface of mast cells. The next time the person comes in contact with that trigger, it interacts with specific IgE on the surface of the mast cells and tells the cells to release chemicals such as histamine. Depending upon the tissue in which they are released, these chemicals will cause a person to have various symptoms. If the mast cells release chemicals in the ears, nose and throat, a person may feel an itching in the mouth and may have trouble breathing or swallowing. If the affected mast cells are in the gastrointestinal tract, the person may have abdominal pain or diarrhea. The chemicals released by skin mast cells, in contrast, can prompt hives.
The ability of a given individual to form IgE against something as benign as food is considered to be an inherited predisposition. generally, allergic people come from families in which allergies are common. Those allergies can be to just about anything - food, pollen, dander or other substances that can cause reactions. Someone with two allergic parents is more likely to develop allergies than someone with one allergic parent.
If you develop severe allergic symptoms (breathing or swallowing difficulties, hives, dizziness or lightheadedness) you should immediately go to the emergency room. These symptoms can be treated with medications such as adrenaline, corticosteroids, antihistamines and intravenous fluids.
If you have a history of severe allergic reactions, (most commonly to bee stings or certain foods) your healthcare provider can prescribe an auto-injector. Auto-injectors are pre-filled syringes that automatically inject epinephrine. They often look like a pen.