Monosodium glutamate (MSG) is used as a flavor-enhancing food additive. It has a bad reputation because many believe it can cause allergy-like symptoms and side effects.

However, much of the evidence for this is anecdotal, and clinical studies on the subject are limited. So what’s the truth about MSG? Is it really as bad as it’s been made out to be?

Despite concerns, decades of research have mostly failed to demonstrate a relationship between MSG and serious reactions. People have reported reactions after eating foods with MSG, but until recently, researchers had been unable to scientifically prove the allergy.

In 2016, researchers found that any amount of MSG is genotoxic, meaning it is damaging to cells and genetic material, as well as to human lymphocytes, a type of white blood cell.

In 2015, it was published that chronic MSG consumption in animals leads to kidney damage.

Another animal study from 2014 revealed that consuming MSG can lead to depressive-like behavior due to changes in serotonin, a neurotransmitter in the brain that affects mood and emotions.

In 2014, Clinical Nutrition Research presented a link between MSG and allergy reactions in a small subset of people who experience chronic hives. The majority of these reports involve mild symptoms though, such as:

  • tingling skin
  • headache
  • a burning sensation in the chest

Larger doses of MSG have also been found to cause symptoms. But those portions are unlikely to be found in restaurant or in grocery store food. After reviewing the evidence in 1995, the U.S. Food and Drug Administration put MSG in the same “generally recognized as safe” category as salt and pepper. A 2009 review published in the journal Clinical & Experimental Allergy came to a similar conclusion.

The exception to the safety of MSG is in children. A 2011 study in Nutrition, Research, and Practice revealed a link between MSG and children with dermatitis. Nevertheless, further research is needed.

Those sensitive to MSG may experience:

  • headache
  • hives
  • runny nose or congestion
  • mild chest pain
  • flushing
  • numbness or burning, especially in and around the mouth
  • facial pressure or swelling
  • sweating
  • nausea
  • digestive upset
  • depression and mood swings
  • fatigue

More serious symptoms may include:

  • chest pain
  • heart palpitations
  • shortness of breath
  • swelling in the throat
  • anaphylaxis

Your doctor may ask if you’ve eaten any food containing MSG within the last two hours if they suspect you have a MSG allergy. A rapid heart rate, abnormal heart rhythm, or a reduction of airflow to the lungs may confirm an MSG allergy.

Most allergic reactions to MSG are mild and go away on their own. More serious symptoms, such as anaphylaxis, require emergency treatment in the form of a shot of epinephrine (adrenaline).

Call your doctor and go to the nearest emergency room immediately if you experience one of the following symptoms:

  • shortness of breath
  • swelling of the lips or throat
  • heart palpitations
  • chest pain

The best treatment for a food allergy is to avoid eating that food. However, according to the U.S. Department of Agriculture, MSG occurs naturally in virtually all food. It’s found in high doses in food that is high in protein, such as:

  • meat
  • poultry
  • cheese
  • fish

Labeling is only required when MSG is added as an ingredient. In those cases, it’s listed as monosodium glutamate.

People with an allergy or intolerance to MSG should avoid packaged and processed foods. Instead, opt for raw foods including fruits, vegetables, and organic meats. Other substances to avoid that are either secondary names or contain MSG include:

  • dried meats
  • meat extracts
  • poultry stocks
  • hydrolyzed protein, which may be used as binders, emulsifiers, or flavor enhancers
  • maltodextrin
  • modified food starch

Food labels may refer to these products as “dried beef,” “chicken stock,” “pork extract,” or “hydrolyzed wheat protein.”

It was previously thought that a very small portion of the population had a reaction to MSG. More recent research suggests that it may be more widespread. Try avoiding the foods listed above if you suspect an MSG allergy. There’s a good chance that you’ll experience only mild discomfort if you eat foods containing MSG.

If you have a complex medical history or tend to have allergies, you might consider limiting your intake of MSG until further research can confirm its safety. You can also test your reaction at home by trying an “elimination diet.” To do this, try removing certain foods from your diet and adding them back in later, while paying close attention to how your body reacts. This may help you pinpoint which substances are causing your allergy or allergies.

Your doctor may put you on a strict avoidance or preservative-free diet and prescribe an epinephrine shot if you’ve experienced severe reactions.