What Is a Food Allergy?
You cannot be allergic to a substance your body hasn't been exposed to. So the first time you eat a food your body decides to attack, you won't have a reaction. This is called sensitizing.
Allergens and Antigens
When the protein, also called an antigen, of the allergenic food meets some of the cells in your body, the cells produce an antibody specifically created to bind to the antigen in the food. These antibodies, also known as Immunoglobulin E (IgE), attach themselves to large cells called mast cells and basophils, forming a complex that is now ready to defend your body.
The next time you come in contact with that food antigen, it fits into the antibody like a key into a lock, releasing chemicals from the mast cells that provoke your body into a response. Those chemicals include histamines, which cause swelling of tissue, itching, hives, breathing problems, and irregular heartbeat. No one knows why this overreaction occurs. Scientists have various theories they are currently studying, but there is no one answer.
Food-allergy symptoms include:
Swelling of the lips, tongue, and mouth
Stuffy nose and congestion
Gastrointestinal (GI) problems (vomiting, diarrhea)
TH1 and TH2 Cells
I never had allergies as a child; why am I allergic now?
You can develop allergies to any substance at any time of your life. Scientists aren't sure why these allergies develop, just that they can. Any time you experience any of the symptoms in the allergy-symptom list, get to a doctor or emergency room for medications that may help prevent a life-threatening reaction.
Your immune system has two main branches of white blood cells that respond to real and perceived attacks on the body. One is called TH1, which is responsible for corralling and neutralizing bacteria and viruses. The other is called TH2 and will respond to substances like protein molecules in food.
These two branches are joined by regulatory cells, which track, monitor, and regulate the TH1 and TH2 cells. It may be that if your immune system isn't stimulated by bacteria and viruses at an early age, the regulatory or helper cells don't learn how to control the TH1 and TH2 cells, and they will overreact. Autoimmune diseases like celiac disease and Multiple Sclerosis can result from overactive TH1 cells. And food allergies result from overactive TH2 cells.