The immune system reacts against nontoxic substances, such as foods, as if they were toxic invaders. Antibodies, programmed to react to some foods, unleash a cascade of immune substances, including histamines. This can inflame tissue and cause severe symptoms of throat closure, shortness of breath, chest tightness, vomiting, itching and hives. These symptoms usually occur immediately after eating the allergenic food or as much as one hour afterward. Massive release of histamine throughout the body can be life threatening.
Many people think they are allergic but, in fact, have food intolerance.
The body's immune system is not involved. Some people develop abdominal discomfort after eating food that has been contaminated by bacteria. Another cause of food intolerance is lactase deficiency. This is a very common condition. Lactase is an enzyme in the gut that degrades lactose, which is found in milk.