Monosodium glutamate (MSG) is a common food additive that enhances the flavor of food. MSG sensitivity is a reaction some people may experience from the additive, although the range and seriousness of symptoms are controversial.

MSG is considered safe by the U.S. Food and Drug Administration (FDA), but a number of people and non-governmental groups contend that MSG can cause serious reactions in some people. The additive is similar to an amino acid called glutamate, which naturally occurs in many foods, as well as in the body.

As an additive, MSG excites the nerves in the tongue and brain, which boost food flavors. In the past 30 years, there have been concerns that MSG, used as a food additive, may be potentially harmful. People reported a wide range of symptoms that they associated with MSG, including headache, sweating, flushing and facial tingling.

Reactions became known informally as Chinese restaurant syndrome, because MSG is often used in Asian cooking (as well as in canned vegetables, soups and processed meats). Some critics believe MSG contributes to Alzheimer’s disease or other long-term or chronic diseases affecting the nervous system or brain. However, studies have concluded that MSG is not connected to serious or long-term reactions, and that the additive does not contribute to Alzheimer’s disease or other chronic diseases.

Several studies have found that a reaction (called MSG Symptom Complex) may occur in some people who eat large amounts of MSG, especially on an empty stomach. Studies have also suggested that people with allergies or asthma may also experience reactions, including difficulty breathing. However, these reactions have not been scientifically confirmed.