The U.S. Food and Drug Administration has classified the food additive monosodium glutamate as generally safe. Even so, some people report side effects after eating food containing MSG, which is commonly used as flavor enhancer in many restaurant meals and packaged foods. Reports of side effects attributed to MSG first appeared in the medical literature in 1968 and included numbness at the back of the neck and arms, weakness and heart palpitations. Other symptoms have since been reported, and debate continues among medical researchers about a possible link to MSG.
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MSG Symptom Complex
In August 1995, the Federation of American Societies for Experimental Biology, or FASEB, published its findings regarding possible MSG-related reactions. Commissioned by the FDA, the report listed a range of possible symptoms associated with MSG consumption: a burning sensation in the back of the neck, forearms and chest; facial pressure or tightness; chest pain; heart palpitations; headache; nausea; numbness in the back of the neck radiating to the arms and back; tingling or warmth in the upper body; drowsiness; and weakness. FASEB referred to these symptoms collectively as MSG symptom complex.
The 1995 FASEB report concluded that MSG may trigger asthma attacks in a small subset of people with asthma who are sensitive to the food additive. This finding was based on 2 earlier studies of MSG consumption in people with asthma, although the FASEB authors noted some deficiencies in the study methods. Subsequent studies have not confirmed this link. A May 2009 review in "Clinical and Experimental Allergy" concluded that the existence of MSG-induced asthma has not been conclusively established, and further research is needed to determine a possible relationship between MSG and asthma.
Hives, Edema, Runny Nose
Other reported side effects of MSG include skin rashes, swelling of the skin, and nasal congestion, itching and sneezing. The authors of the May 2009 report in "Clinical and Experimental Allergy" agreed with earlier findings and concluded that MSG may, in rare cases, cause hives and skin swelling in people who are very sensitive to the additive. The authors also noted that a small number of cases of nasal symptoms possibly related to MSG consumption have been reported. In the handful of patients involved, nasal symptoms disappeared when they followed an additive-free diet.
Onset and Duration of Side Effects
The possible side effects included in MSG symptom complex reportedly occur within 15 to 30 minutes of consuming MSG and go away on their own within 2 hours. In the rare cases when asthma attacks may have been linked to eating foods containing MSG, symptoms were noted within 1 to 12 hours of consumption. In limited studies of people with chronic hives, MSG consumption triggered skin reactions within 1 to 24 hours in a small subset of people with apparent sensitivity to the additive.