Normally, your body's immune system defends against potentially harmful substances, such as bacteria, viruses, and toxins. In some people, an immune response is triggered by a substance that is generally harmless, such as a specific food.
The cause of food allergies is not fully understood, because they can produce such a variety of symptoms. Reactions to foods may vary from mild to fatal.
While many people have a food intolerance, food allergies are less common. In a true food allergy, the immune system produces antibodies and histamine in response to the specific food.
The symptoms may be confined mainly to the stomach and intestines, or may involve many parts of the body after the food is digested or absorbed. The symptoms usually begin immediately, seldom more than 2 hours after eating. Rarely, the symptoms may begin hours after eating the offending food.
Asthma, eczema, or other disorders may be triggered or worsened by food allergies.
Any food can cause an allergic reaction, but a few foods are the main culprits. In children, the most common food allergies are to:
- eggs
- peanuts
- milk
- soy
- tree nuts
- wheat
- shellfish (shrimp, crab, lobster, snails, clams)
Fortunately, many children will outgrow their allergy to milk, egg, wheat, and soy by the time they are five years old if they avoid the offending foods when they are young. Allergies to peanuts, tree nuts, and shellfish tend to be lifelong.
In older children and adults, the most common food allergies are:
- peanuts
- tree nuts
- shellfish
- fish
It is controversial whether food additives -- such as dyes, thickeners, and preservatives -- likely cause a true allergic reaction.
Many Americans believe they have food allergies, while in reality fewer than 1% have true allergies. Most people's symptoms are caused by intolerances to foods such as:
A food allergy frequently starts in childhood, but it can begin at any age.
