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.
If a person does not have enough lactase, the body cannot digest the lactose present in most milk products. Instead, the lactose is used by bacteria, gas is formed and the person develops bloating, abdominal pain and sometimes diarrhea. The foods that people react to are those that are eaten more frequently. In Japan, for example, rice allergy is more frequent, while in Italy, allergy to tomato is common. What's scary about food allergy is that even a tiny amount of food can trigger a severe reaction.