The Facts About Food Allergy

For someone with a food allergy, eating or swallowing even a tiny amount of a particular food can cause symptoms such as skin rash, nausea, vomiting, cramping, and diarrhea.

Because the body is reacting to something that is otherwise harmless, this type of allergic reaction is often called a hypersensitivity reaction. Rarely, a severe allergic reaction can cause a life-threatening set of symptoms called anaphylaxis, or anaphylactic shock.

Although about 25% of people believe they have a food allergy, only about 2.5% of adults and about 6-8% of children, mainly younger than 6 years, have true food allergies. The rest have what is known as food intolerance an undesirable reaction to a food that does not involve the immune system.

It is easy to confuse food intolerance with food allergy because they can have similar symptoms. With food intolerance, however, you usually get only mild symptoms such as an upset stomach.

A common example of food intolerance is lactose intolerance a condition in which a person is missing a certain enzyme necessary to digest dairy proteins. The result is loose stools, gas, and nausea after consuming dairy products such as milk or cheese.

Another example of food intolerance is reaction to MSG. MSG, or monosodium glutamate, is a white-colored additive used to enhance the flavor of food. It is a fermented mixture of glutamic acid, sodium, and water and is used mainly in Asian cooking. Over the last 30 years, side effects from MSG have been related to its use in Chinese food and referred to as the Chinese restaurant syndrome.

In this syndrome, MSG was suggested as the cause of the symptoms following a Chinese meal. In 1995, a new term was coined, the MSG symptom complex, to include all the reactions that were reported to be related to MSG. These reactions are not a true food allergy, and the exact cause of the reactions is unknown.

An allergic reaction occurs when the body's immune system overreacts to an allergen, in this case a food protein.

The white blood cells produce an antibody to this allergen, called immunoglobulin E or IgE. When this antibody comes in contact with the particular food protein, it promotes production and release of certain chemicals called "mediators." Histamine is an example of a mediator. These mediators act on various parts of the body, mainly the skin, throat, airways, intestines, and heart.

The effects of the mediators on organs and other cells cause the symptoms of the allergic reaction. Any food has the potential to trigger an allergic reaction, but a few foods account for most food allergies.

Generally, people who have allergies react to only a few foods. Occasionally a person who is allergic to one food also may be allergic to other related foods. This is called cross-reaction. People who have a history of other allergies, such as eczema or asthma, are particularly prone to having a reaction to a food. They are also more likely to have a more severe reaction.