Food allergies can cause serious illness or death. The most common food allergies are to proteins in cow's milk, eggs, peanuts, wheat, soy, fish, shellfish, and tree nuts. In people with food allergies, even a tiny amount of the food can trigger an immune response. Peanuts and tree nuts are the leading causes of severe food allergic reactions. In the immune response, IgE antibodies cause mast cells (type of immune system cell) to release chemicals into the bloodstream. Histamine, one of these chemicals, causes many of the symptoms listed below. Anaphylaxis occurs when several of these symptoms occur simultaneously and may include decreased blood pressure, narrowed airways in the lungs, and tongue swelling.