It is estimated that about twelve million Americans suffer from food allergies.Any food can cause an allergy, but there are eight foods that account for 90 percent all allergic reactions. The "Big Eight" are milk eggs, peanuts, tree nuts, fish, shellfish, soy, and wheat. The most common food allergies for children are different from those for adults.Milk is the most common food allergy in childhood. About 2.5 percent of children under the age of three are allergic to milk, and nearly all of them develop the allergy within their first year. However, most children will outgrow this allergy by the age of six.For adults, shellfish is the most common food allergy. Shellfish allergies often happen later in life, unlike many other food allergies. The most common kinds of shellfish that adults are allergic to are shrimp, crab, and lobster.People get food allergies when their immune system mistakes a food as harmful. The body reacts by creating antibodies. Symptoms develop when the antibodies fight the offending food. For some people who are very sensitive, even consuming a tiny amount of a food can trigger a reaction. In some cases, people do not even have to eat the food. For example, someone who is severely allergic to peanuts can have a reaction just by sitting next to a person who is eating them.Allergic symptoms and reactions can range from annoying to deadly. Some people may experience nothing more than slight itching. However, some people immediately feel their throat start to close and are unable to breath. That is why people with serious allergies should always have medication on hand in case of an emergency.